can i get too little backpressure
02-08-2001, 02:59 PM
#1
Junior Member
Thread Starter
Join Date: Dec 1999
Location: Fillmore, Il USA
Posts: 6
Likes: 0
Received 0 Likes
on
0 Posts
can i get too little backpressure
my setup is a 350tpi with hooker headers, y-pipe, and flowmaster muffler. My problem is that the car has terrible throttle response. As well the sound coming from the exhaust sounds like someone beating on an empty metal trash can. My question is, does this setup have to little backpressure? What can I do to add some? My goal here is to get rid of the trash can sound from the exhaust and maybe solve my throttle response problem, or at least eliminate a possibility.
02-08-2001, 03:20 PM
#2
Banned
Join Date: Jul 2000
Posts: 1,384
Likes: 0
Received 0 Likes
on
0 Posts
You didn't say whether or not you had a cat on there or if it was gutted.
If you have no cat and or it's gutted, than yes you will lose low end torque. Something the TPI system is the best at.
------------------
91 Formula
305 TPI 5speed
1LE/G92/WS6
Paxton SN93, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL, Holley 9mm wires, fastchip, Bosch O2sensor, Bosch in-line pump(w/stock pump), SLP headers & catback,short shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
If you have no cat and or it's gutted, than yes you will lose low end torque. Something the TPI system is the best at.
------------------
91 Formula
305 TPI 5speed
1LE/G92/WS6
Paxton SN93, SLP airfoil, ported/polished plenum, March pulleys, Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL, Holley 9mm wires, fastchip, Bosch O2sensor, Bosch in-line pump(w/stock pump), SLP headers & catback,short shifter,3:73s w/Auburn posi,170* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
02-08-2001, 05:14 PM
#4
Supreme Member
Join Date: Sep 1999
Location: Manassas VA
Posts: 3,197
Likes: 0
Received 6 Likes
on
5 Posts
Car: 04 GTO
Engine: LS1
Transmission: M12 T56
No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.
Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.
Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.
The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through...ed
------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die
Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.
Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.
The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through...ed
------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die
The following users liked this post:
ughmas (04-03-2022)
02-08-2001, 05:29 PM
#5
Banned
Join Date: Jan 2001
Location: Belleville, IL USA
Posts: 1,429
Likes: 0
Received 0 Likes
on
0 Posts
Great explaination Ed.
He is right. you do not have too much backpressure. From the sound of things you may have an exhaust leak or two, so check those things out. An exhaust leak can really hurt power significantly.
good luck
He is right. you do not have too much backpressure. From the sound of things you may have an exhaust leak or two, so check those things out. An exhaust leak can really hurt power significantly.
good luck
02-08-2001, 05:50 PM
#6
Moderator
iTrader: (14)
Join Date: Mar 2000
Location: Littleton, CO USA
Posts: 43,169
Likes: 0
Received 35 Likes
on
34 Posts
Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Thank you, Ed, thank you very much. This thread should be bookmarked so it can be referenced everytime a magazine mechanic mentions "too little backpressure" (or is that "to little backpressure"?) causing loss of power. Those who have tried to run an engine with no manifolds (open exhaust ports) falsely assumed the engine craved "back pressure", where in truth it is the phenomenon you describe.
One other possibility beyond what you mentioned is that in the old days, improved exhaust flow could cause a lean-out of the mixture. With mechanical open-loop systems, that was a very real problem if you didn't re-jet to compensate. HOOK doesn't say what kind of induction he has, but perhaps that is part of his problem.
I had drafted up a potential tech article on this as well as info on why TPI's die at 5000 rpm. Perhaps you've saved the trouble on the exhaust side.
To all those still in high school or college: Stay awake in physics class. Save Ed the "carpool tunnel"...
P.S.: Wouldn't hurt to stay awake in English class, either.
------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/LB9 block, ZZ3 cam and intake, WP 305 heads ported & polished, Hooker headers & y-pipe, hi-flow cat).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, 3.08 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.
One other possibility beyond what you mentioned is that in the old days, improved exhaust flow could cause a lean-out of the mixture. With mechanical open-loop systems, that was a very real problem if you didn't re-jet to compensate. HOOK doesn't say what kind of induction he has, but perhaps that is part of his problem.
I had drafted up a potential tech article on this as well as info on why TPI's die at 5000 rpm. Perhaps you've saved the trouble on the exhaust side.
To all those still in high school or college: Stay awake in physics class. Save Ed the "carpool tunnel"...
P.S.: Wouldn't hurt to stay awake in English class, either.
------------------
82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R. 2.93 limited slip. Cat-back from '91 GTA, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 w/LB9 block, ZZ3 cam and intake, WP 305 heads ported & polished, Hooker headers & y-pipe, hi-flow cat).
57 Bel Air, my 1st car. 0.030 over 396, Weiand Action+, Edelbrock 1901 Q-Jet, Jacobs Omnipack, 1-3/4" headers, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, 3.08 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Best 15.1 @ 5800' Bandimere. Daily driver while Camaro was being put together.
12-02-2001, 11:23 PM
#7
Supreme Member
Join Date: Aug 2001
Location: Western NY
Posts: 1,108
Likes: 0
Received 1 Like
on
1 Post
Car: 2007 Saturn Sky Redline
Engine: 2.0 turbo
Transmission: m5
Axle/Gears: 3.91 LSD
So basically match your headers to your engine 1 3/4 for 350 and you're set is what I get out of this, and if you get long tubes you're better off than shorties.
Trending Topics
12-02-2001, 11:27 PM
#8
turn up your fuel pressure
------------------
-Tas
'89 Formula WS-6
305, TBI, 700R4, P.A.W. 14x3 open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips, Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248)
Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
------------------
-Tas
'89 Formula WS-6
305, TBI, 700R4, P.A.W. 14x3 open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips, Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248)
Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options
12-03-2001, 05:21 AM
#10
Supreme Member
Join Date: Nov 2000
Location: So. Cal, L.A.
Posts: 1,069
Likes: 0
Received 1 Like
on
1 Post
Car: '88 Firebird Formula 350
Engine: Built 383 TPI
Transmission: Built 700r4
Axle/Gears: 9 bolt, 3.27:1 Posi
I do agree for the most part with Ed, but with out any backpressure, you wouldn't be running as efficient as possible. On a street driven car, you need some for gas milage, sound muffeling, and low end torque. Muffler companies prove this. Ever run open headers? Off the line it sounds like you have more power, but it doesn't feel like it. But the power really kicks in at higher rpms.
The trash can banging sound is the headers. The thin wall design of the headers don't insulate the sound, (or heat) as well as the stock manifolds.
------------------
'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...
http://www.spinfrenzy.com/stingerssx...easures.html#4
The trash can banging sound is the headers. The thin wall design of the headers don't insulate the sound, (or heat) as well as the stock manifolds.
------------------
'82 Firebird, dead stock, 9 bolt disc rear, over 200,000 miles and still going strong, more to come...
http://www.spinfrenzy.com/stingerssx...easures.html#4
12-03-2001, 10:22 PM
#11
Supreme Member
Join Date: Sep 1999
Location: Manassas VA
Posts: 3,197
Likes: 0
Received 6 Likes
on
5 Posts
Car: 04 GTO
Engine: LS1
Transmission: M12 T56
Mufflers also act as a shield against reversion from the exit of the exhaust. And also, mufflers are far downstream, where their actual effects on scavenging is minimal. Take into account the inefficency of the whole system, and the loss through a good muffler alone is minimal.
And since backpressure would be lowest at lower rpms, since the engine is moving less air. Thus, any losses in torque make more sense to come from the lack of velocity through an exhaust designed to move more air.
Comparisons of open exhaust vs. mufflers doesn't tell me much, we all know how easy it is to skew results with tuning/optimization, as well as error in the dyno equipment, weather, etc. I mean, if their claims are true then how could backpresure be good if seemingly similar flowing mufflers produce such different power output.
And since backpressure would be lowest at lower rpms, since the engine is moving less air. Thus, any losses in torque make more sense to come from the lack of velocity through an exhaust designed to move more air.
Comparisons of open exhaust vs. mufflers doesn't tell me much, we all know how easy it is to skew results with tuning/optimization, as well as error in the dyno equipment, weather, etc. I mean, if their claims are true then how could backpresure be good if seemingly similar flowing mufflers produce such different power output.
12-03-2001, 11:22 PM
#12
<font face="Verdana, Arial" size="2">Originally posted by rezinn:
Actually, that tinny beating-on-a-garbage-can type sound is just flowmaster, they sound like that.</font>
Actually, that tinny beating-on-a-garbage-can type sound is just flowmaster, they sound like that.</font>
12-27-2002, 02:44 AM
#13
Supreme Member
Join Date: Oct 2002
Location: Oklahoma City, OK
Posts: 1,042
Likes: 0
Received 0 Likes
on
0 Posts
Car: 92 Z28
Engine: 357 TPI (L98)
Transmission: 700R4
How should one know what size primaries (and for that matter, exhaust system) to use without being too big or too small? It would be awesome if you experienced guys could make a chart that corresponded engine output to recommended primary/exhaust size. What do you think? It would really help out those newbies like me!
01-03-2003, 12:49 PM
#14
Member
Join Date: May 2002
Location: SW Chicago, Garfield Ridge
Posts: 121
Likes: 0
Received 0 Likes
on
0 Posts
the garbage can noise might be your muffler vibrating on the heat shield, just a thought because mine was doing that untill i fixed the heat shield from hanging, or it might be hitting something else. just a thought
01-03-2003, 02:02 PM
#15
Supreme Member
Join Date: Jul 1999
Location: Loveland, OH, US
Posts: 18,457
Likes: 0
Received 14 Likes
on
14 Posts
Car: 4
Engine: 6
Transmission: 5
I had a Blowmaster for a short while, I absolutely could not stand it. It was like driving around with a 55-gallon drum riding in a shopping cart right behind the car all the time. The most obnoxious, unpleasant, bogus-sounding noise I had ever heard out of the car. I took it off and put a Dynomax on it. And you're right, I didn't really have enough flow; all I had in front of it at the time was a 400 with double-hump heads, a Comp 282 solid cam, a 800 CFM Holley, and a few other goodies. No doubt a TPI 305 would have had enough flow to sound really good. 
If you just walk up to one of those mufflers and tap on it, you'll know instantly why it sounds like that: it might as well be a 55-gallon drum the way it sounds all by itself.
The back-pressure info is excellent. It's one of those myths that just refuses to go away, kind of like how running a high-volume oil pump in a stock motor will lube the bearings better, or how a bigger carb on a smaller motor runs rich, or how their TPI car "makes power" (unlike every other one in existence) above 5000 RPM. All of these things are reasons why so many people struggle to get their car to really run right: the myths get in the way of logic and understanding, and people who don't know better hear them so often from other people that also don't know better, they think there must be something to them.
If you just walk up to one of those mufflers and tap on it, you'll know instantly why it sounds like that: it might as well be a 55-gallon drum the way it sounds all by itself.The back-pressure info is excellent. It's one of those myths that just refuses to go away, kind of like how running a high-volume oil pump in a stock motor will lube the bearings better, or how a bigger carb on a smaller motor runs rich, or how their TPI car "makes power" (unlike every other one in existence) above 5000 RPM. All of these things are reasons why so many people struggle to get their car to really run right: the myths get in the way of logic and understanding, and people who don't know better hear them so often from other people that also don't know better, they think there must be something to them.
03-13-2003, 02:57 PM
#18
Supreme Member
Join Date: Apr 2001
Location: USA
Posts: 4,969
Likes: 0
Received 0 Likes
on
0 Posts
Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
Originally posted by jamesbob02
How should one know what size primaries (and for that matter, exhaust system) to use without being too big or too small? It would be awesome if you experienced guys could make a chart that corresponded engine output to recommended primary/exhaust size. What do you think? It would really help out those newbies like me!
How should one know what size primaries (and for that matter, exhaust system) to use without being too big or too small? It would be awesome if you experienced guys could make a chart that corresponded engine output to recommended primary/exhaust size. What do you think? It would really help out those newbies like me!
There's a chart in there that tells a good tale about what size primaries to use. It's formed by calculations he developed based on dyno runs. I swear the guy must have a calculator perched on his belly 95% of the day.
Granted, with any formula, there's always "the exception", but for what the average street guy needs, it's more that adequate.
Last edited by AJ_92RS; 03-13-2003 at 03:02 PM.
03-16-2003, 12:16 AM
#19
Junior Member
Join Date: Feb 2003
Posts: 55
Likes: 0
Received 0 Likes
on
0 Posts
lol so I am assuming a 3 inch dual piping with 2 high flow cats and 2 Borla Xr1 mufflers would be a bit much for a street driven LO3 camaro that is about to recieve a higher flowing set of heads manifold TBI unit and semi aggressive cam with a 3000 rpm stall converter??? hahaha
Prolly be in the 270hp area....
I mean 3 inch off each header running 2 3 inch pipes all the way back with 1 cat per pipe going back into 2 mufflers....
Prolly be in the 270hp area....
I mean 3 inch off each header running 2 3 inch pipes all the way back with 1 cat per pipe going back into 2 mufflers....
03-16-2003, 12:21 AM
#20
Junior Member
Join Date: Feb 2003
Posts: 55
Likes: 0
Received 0 Likes
on
0 Posts
this isnt my car but this is what I meant....
By the way I ran open shorties on my stang for like 15 blocks or so on my way to the exhuast shop... low end sucked horribley but WOW top end was DAMN impressive!!! She screamed to 6000rpms and felt like she was still pulling!
By the way I ran open shorties on my stang for like 15 blocks or so on my way to the exhuast shop... low end sucked horribley but WOW top end was DAMN impressive!!! She screamed to 6000rpms and felt like she was still pulling!
07-05-2005, 11:08 PM
#21
Originally posted by Ed Maher
No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.
Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.
Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.
The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through...ed
------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die
No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.
Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.
Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.
The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through...ed
------------------
Ed Maher - Moderator @ The Carb Board
92 Z28 Convertible - Quasar blue / Tan top
LB9 4L60 GU2 G80 - stock, soon to be sleeper
- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die
07-06-2005, 11:30 AM
#22
Moderator
iTrader: (14)
Join Date: Mar 2000
Location: Littleton, CO USA
Posts: 43,169
Likes: 0
Received 35 Likes
on
34 Posts
Car: 82 Berlinetta/57 Bel Air
Engine: LS1/LQ4
Transmission: 4L60E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
You've affected your PROM tuning. MAF systems aren't as affected by changes in exhaust performance, but SD is. So, to reap the benefits of reduced back pressure with SD systems, you need to retune.
There is one other negative effect to reducing back pressure that hasn't been addressed here. The factory used "positive pressure" EGR valves on a lot of engines. It relied on some pressure in the exhaust to open up the valve when commanded. Eliminating backpressure can actually keep that type of valve from opening (seems to be an issue with TBI motors more than TPI). The fix, of course, is to replace the valve with an aftermarket replacement "negative" pressure valve.
There is one other negative effect to reducing back pressure that hasn't been addressed here. The factory used "positive pressure" EGR valves on a lot of engines. It relied on some pressure in the exhaust to open up the valve when commanded. Eliminating backpressure can actually keep that type of valve from opening (seems to be an issue with TBI motors more than TPI). The fix, of course, is to replace the valve with an aftermarket replacement "negative" pressure valve.
07-06-2005, 12:46 PM
#23
Supreme Member
Join Date: Jun 2001
Location: Charleston, SC
Posts: 9,550
Likes: 0
Received 2 Likes
on
2 Posts
Car: 91 Camaro Vert
Engine: 02 LS1, HX40
Transmission: 2002 LS1 M6
Originally posted by five7kid
There is one other negative effect to reducing back pressure that hasn't been addressed here. The factory used "positive pressure" EGR valves on a lot of engines. It relied on some pressure in the exhaust to open up the valve when commanded. Eliminating backpressure can actually keep that type of valve from opening (seems to be an issue with TBI motors more than TPI). The fix, of course, is to replace the valve with an aftermarket replacement "negative" pressure valve.
There is one other negative effect to reducing back pressure that hasn't been addressed here. The factory used "positive pressure" EGR valves on a lot of engines. It relied on some pressure in the exhaust to open up the valve when commanded. Eliminating backpressure can actually keep that type of valve from opening (seems to be an issue with TBI motors more than TPI). The fix, of course, is to replace the valve with an aftermarket replacement "negative" pressure valve.
yea, way back when the vert was a stock L03, i had that issue....
07-06-2005, 01:19 PM
#24
Supreme Member
iTrader: (2)
Join Date: Mar 2004
Location: Kissimmee, FL
Posts: 1,941
Likes: 0
Received 0 Likes
on
0 Posts
Car: 1991 Camaro RS
Engine: 357cid
Transmission: T5 Swap
Axle/Gears: 10bolt 7.5" 3.23 soon to be 3.73
theres alot to read here but i dont think i saw this bit of info......
When you open up the Intake flow or the Exhaust flow you dont lose power at all..... you are simply changing the power curve.
Taking the exhaust off of your car will move the powerband up to a higher area...
btw im running Hooker supercomp full length headers, 3" true dual exhaust, flowmaster 40s. All on a LO3 305. oh and i think that flowmasters sound awsome, and not only on small engines.
I heard a 2nd gen with a 454cid Rat and huge cam,etc with flowmasters and all i can say is it got me a chubby
When you open up the Intake flow or the Exhaust flow you dont lose power at all..... you are simply changing the power curve.
Taking the exhaust off of your car will move the powerband up to a higher area...
btw im running Hooker supercomp full length headers, 3" true dual exhaust, flowmaster 40s. All on a LO3 305. oh and i think that flowmasters sound awsome, and not only on small engines.
I heard a 2nd gen with a 454cid Rat and huge cam,etc with flowmasters and all i can say is it got me a chubby
07-06-2005, 04:02 PM
#25
Supreme Member
Join Date: Apr 2001
Location: USA
Posts: 4,969
Likes: 0
Received 0 Likes
on
0 Posts
Car: yy wife, crazy.
Engine: 350, Vortecs, 650DP
Transmission: TH-350
Axle/Gears: 8.5", 3.42
Originally posted by Saigon_Bob
When you open up the Intake flow or the Exhaust flow you dont lose power at all..... you are simply changing the power curve.
Taking the exhaust off of your car will move the powerband up to a higher area...
When you open up the Intake flow or the Exhaust flow you dont lose power at all..... you are simply changing the power curve.
Taking the exhaust off of your car will move the powerband up to a higher area...
I think a better way to say it would be "will improve the powerband...."
It will extend your useable RPM range a few hundred (i.e. increase upper RPM HP), but it doesn't "move the powerband up". There should be no loss in low-mid RPM torque because you let the engine breath easier.
This whole "backpressure" excuse was thought up by people that didn't know how to tune a carb. Basically what happens is the a/f mixture (as five7kid pointed out) goes lean. Of course this causes a loss in power. You're starving the engine for fuel.
DanTheMan_smlk,
Are you sure your seat-of-the-pants meter isn't being fooled by the new sound you're hearing? People do something (like make a car louder) and think that means more power. You may have increased the power, but it may not be as much as you're ears (or your expectations) are telling you it should be. That can lead you into thinking you didn't gain any power at all.
Do you have any recorded times from before and after you changed the exhaust? That's the only true way to tell. The butt dyno does not always tell the truth.
07-06-2005, 08:55 PM
#26
Originally posted by AJ_92RS
DanTheMan_smlk,
Are you sure your seat-of-the-pants meter isn't being fooled by the new sound you're hearing? People do something (like make a car louder) and think that means more power. You may have increased the power, but it may not be as much as you're ears (or your expectations) are telling you it should be. That can lead you into thinking you didn't gain any power at all.
Do you have any recorded times from before and after you changed the exhaust? That's the only true way to tell. The butt dyno does not always tell the truth.
DanTheMan_smlk,
Are you sure your seat-of-the-pants meter isn't being fooled by the new sound you're hearing? People do something (like make a car louder) and think that means more power. You may have increased the power, but it may not be as much as you're ears (or your expectations) are telling you it should be. That can lead you into thinking you didn't gain any power at all.
Do you have any recorded times from before and after you changed the exhaust? That's the only true way to tell. The butt dyno does not always tell the truth.
thanks for explaining this
07-06-2005, 11:02 PM
#27
Moderator
When I had my headers and open y pipe, the car did seem a little less responsive in the torque area as well. But man did that thing pull really nice up top when I went WOT.
08-31-2015, 02:56 PM
#28
Junior Member
Join Date: Sep 2013
Posts: 52
Likes: 0
Received 0 Likes
on
0 Posts
Re: can i get to little backpressure
Hi Ed,
I have a 89 TA with a stroked 383 and many aftermarket parts.
It ran beautifully when I purchased for my son.
Recently it started idling poorly ( surging and sometimes die)
I have replaced every part. MAF, IAC;TPS O2, coolant, knock, even a different ECM , rebuilt the distributor, plugs, wires, cap and rotor.
Still have the same problem.
After replacing distributor I went to set timing and it won't advance until over 3/4 throttle travel at which time the timing jumps to around 30 deg. and the motor screams to life.
Any thoughts and why their is no gradual timing advance.
the distributor I put in is the exact same part number as I took out. It has no mechanical advance weights.
Thanks
I have a 89 TA with a stroked 383 and many aftermarket parts.
It ran beautifully when I purchased for my son.
Recently it started idling poorly ( surging and sometimes die)
I have replaced every part. MAF, IAC;TPS O2, coolant, knock, even a different ECM , rebuilt the distributor, plugs, wires, cap and rotor.
Still have the same problem.
After replacing distributor I went to set timing and it won't advance until over 3/4 throttle travel at which time the timing jumps to around 30 deg. and the motor screams to life.
Any thoughts and why their is no gradual timing advance.
the distributor I put in is the exact same part number as I took out. It has no mechanical advance weights.
Thanks
08-31-2015, 03:01 PM
#29
Junior Member
Join Date: Sep 2013
Posts: 52
Likes: 0
Received 0 Likes
on
0 Posts
Re: can i get to little backpressure
Hi Ed,
I have an 89 TA with a stroked 383.
It has headers and I can't keep plug wires from melting down literally.
I can I check to see if my Catalytic converter is partially plugged and can that cause surging at idle. I have changed every sensor I know is on the car with no change in surging.
Thanks
I have an 89 TA with a stroked 383.
It has headers and I can't keep plug wires from melting down literally.
I can I check to see if my Catalytic converter is partially plugged and can that cause surging at idle. I have changed every sensor I know is on the car with no change in surging.
Thanks
03-29-2022, 08:38 AM
#30
Member
Re: can i get to little backpressure
I wouldn't say that.
I think a better way to say it would be "will improve the powerband...."
It will extend your useable RPM range a few hundred (i.e. increase upper RPM HP), but it doesn't "move the powerband up". There should be no loss in low-mid RPM torque because you let the engine breath easier.
This whole "backpressure" excuse was thought up by people that didn't know how to tune a carb. Basically what happens is the a/f mixture (as five7kid pointed out) goes lean. Of course this causes a loss in power. You're starving the engine for fuel.
DanTheMan_smlk,
Are you sure your seat-of-the-pants meter isn't being fooled by the new sound you're hearing? People do something (like make a car louder) and think that means more power. You may have increased the power, but it may not be as much as you're ears (or your expectations) are telling you it should be. That can lead you into thinking you didn't gain any power at all.
Do you have any recorded times from before and after you changed the exhaust? That's the only true way to tell. The butt dyno does not always tell the truth.
I think a better way to say it would be "will improve the powerband...."
It will extend your useable RPM range a few hundred (i.e. increase upper RPM HP), but it doesn't "move the powerband up". There should be no loss in low-mid RPM torque because you let the engine breath easier.
This whole "backpressure" excuse was thought up by people that didn't know how to tune a carb. Basically what happens is the a/f mixture (as five7kid pointed out) goes lean. Of course this causes a loss in power. You're starving the engine for fuel.
DanTheMan_smlk,
Are you sure your seat-of-the-pants meter isn't being fooled by the new sound you're hearing? People do something (like make a car louder) and think that means more power. You may have increased the power, but it may not be as much as you're ears (or your expectations) are telling you it should be. That can lead you into thinking you didn't gain any power at all.
Do you have any recorded times from before and after you changed the exhaust? That's the only true way to tell. The butt dyno does not always tell the truth.
The exhaust flows so well right now but the exhaust pulses are very slow at low RPM and do not have the proper scavenging effect at the RPMs the TPI manifold makes power at, and when the exhaust would make better power at higher RPMs, the TPI is choking the motor down. Your exhaust needs to be tuned to match the intake, cam, heads etc.
Here is a great video explaining it in GREAT detail:
03-30-2022, 04:33 PM
#31
Re: can i get to little backpressure
No you will lose low end power with exhaust that isn't tuned for the engine. I have a L98 with a Comp Cams Computer controlled cam (210/220 @ 0.050", 0.500"/0.510" lift, 114 LSA) with a stock TPI intake (mildly ported plenum), Stock heads (milled 0.010"), and SLP 1 3/4" shorty headers. I have the pipes open where the cats would be (for now) and I lost a lot of low end torque. I have an AFR gauge and I tune the car with an AFPR for now unless I decide on getting an EBL P4 flash tuneable ECM. (I'm waiting on parts for an LS3 stroker swap so I'm reluctant on spending money on the L98 but I'm kind of having fun pushing this old tech as far as I can for cheap).
The exhaust flows so well right now but the exhaust pulses are very slow at low RPM and do not have the proper scavenging effect at the RPMs the TPI manifold makes power at, and when the exhaust would make better power at higher RPMs, the TPI is choking the motor down. Your exhaust needs to be tuned to match the intake, cam, heads etc.
Here is a great video explaining it in GREAT detail: https://www.youtube.com/watch?v=jjPeP_Nn2B4
The exhaust flows so well right now but the exhaust pulses are very slow at low RPM and do not have the proper scavenging effect at the RPMs the TPI manifold makes power at, and when the exhaust would make better power at higher RPMs, the TPI is choking the motor down. Your exhaust needs to be tuned to match the intake, cam, heads etc.
Here is a great video explaining it in GREAT detail: https://www.youtube.com/watch?v=jjPeP_Nn2B4
03-30-2022, 05:36 PM
#32
Member
03-31-2022, 12:19 PM
#33
Supreme Member
Join Date: Oct 2000
Location: Park City, UT
Posts: 1,890
Received 272 Likes
on
190 Posts
Car: '92 Corvette
Engine: LT1
Transmission: ZF6
Axle/Gears: 3.45
Re: can i get to little backpressure
No it's not. The OP was talking about his beater, that runs poorly and likely has tuning issues...then presumably comparing that to the stock system. Your post (which was super vague and unclear) was about your combo, which either has issues, or you haven't actually measured what it can do. Do you know where TPI actually "makes power at"?
The following users liked this post:
OrangeBird (03-31-2022)
03-31-2022, 12:51 PM
#34
Re: can i get to little backpressure
No it's not. The OP was talking about his beater, that runs poorly and likely has tuning issues...then presumably comparing that to the stock system. Your post (which was super vague and unclear) was about your combo, which either has issues, or you haven't actually measured what it can do. Do you know where TPI actually "makes power at"?
03-31-2022, 02:09 PM
#35
Member
Re: can i get to little backpressure
No it's not. The OP was talking about his beater, that runs poorly and likely has tuning issues...then presumably comparing that to the stock system. Your post (which was super vague and unclear) was about your combo, which either has issues, or you haven't actually measured what it can do. Do you know where TPI actually "makes power at"?
I used my car as an example. The fact you do not know that the TUNED port Injection manifold is TUNED (its in the name FFS) for power from the low to mid range of what a stock SBC can rev to and starts to run out of power near 4500-4700 rpm shows your ignorance. Runner length is one of the MAIN factors of intake charge strength due to the harmonics of the pressure waves reflecting off of the intake valves when they close. Engineers typically try and take advantage of the 2nd harmonic as it is the strongest one. Why do you think many engines have multiple length runners for low and high end power and have a valve to switch between them at the RPM they start to overlap? HMMMMM...
Here is another excellent video explaining it:
These AREN'T my videos. They are by Engineering Explained which is a highly popular channel with over 3 million subscribers. None of them are probably you.
Your attitude is not welcome when I'm trying to inform people of correct technical information and being challenged by people absolutely ignorant of the subject at hand.
03-31-2022, 02:10 PM
#36
Member
Re: can i get to little backpressure
And these AREN'T my videos. They are by Engineering Explained which is a highly popular channel with over 3 million subscribers.
03-31-2022, 03:26 PM
#37
Supreme Member
Join Date: Oct 2000
Location: Park City, UT
Posts: 1,890
Received 272 Likes
on
190 Posts
Car: '92 Corvette
Engine: LT1
Transmission: ZF6
Axle/Gears: 3.45
Re: can i get to little backpressure
No, my combo doesn't have issues besides not having the proper exhaust for the rest of the engine set as I already explained. I've been a professional dealership tech for GM and Mopar dealerships for over 20 years, I have been an ASE Master tech for just about as long, and not only was a California certified Smog program instructor working at WyoTech in the West Sacramento campus for 5 years. I also taught the High Performance Powertrains program there and even helped write the curriculum. I was also a certified Subject Matter Expert for the State and was used in Court cases regarding automotive technology and helped write the test questions for the Bureau of Automotive Repair for the Smog program.
Or your own no-low-end tork'in, car?
What's this got do do w/the OP's crappy exhaust...again?
Hey, I get it that you don't like being challenged. That is obvious. 
Look, you claimed that you put on SLP headers and some open exhaust and "lost low end tork". Right? That's what you typed...IDK if that is what you were actually trying to say. Your use of your car as an example is pretty worthless b/c there was no context, no data and it's unclear what you actually even have! All we really know is that you have a shitty combo with no low end torkin' exhaust combined with no top endin' TPI. The real questions I have are:
1. What did you lose low end torque compared to,
2. How much low end torque (tq from idle to ~2500) did you actually lose? and
3. What exhaust? It SOUNDS like you have SLP headers and Y pipe....and the end of the SLP Y pipe is the end of your exhaust system?
:bigears
.
Last edited by Tom 400 CFI; 03-31-2022 at 03:45 PM.
The following users liked this post:
OrangeBird (03-31-2022)
03-31-2022, 03:57 PM
#38
Member
Re: can i get to little backpressure
I am VERY well aware of the RPM that TPI "makes" power. VERY well aware. Unfortunately, it is you, who is the ignorant among us....in spite of you auto-tech past. TPI makes MID RANGE POWER. Mid range. Not low end, not high end (which you seem to recognize that...at least), but it "makes power", right in the middle. 3200 RPM or so. How do we know this? Well, if we look at dyno pulls that start at idle and run past hp peak, we can see where the surge is in tq, due to the tuned runner length, and compare that to the same engine w/o TPI. What we see is similar TQ on the "low end" which I'd call from idle to about 2500. Then we see the "TPI Tork surge" starting around 2500 and lasting through about 3600? 3700?....where a similar engine w/o TPI makes less tq. Above that...what I'd call the high end, TPI falls off compared to other intakes. Making this comparison shows us that the TPI most certainly does NOT make a meaningful or noteworthy amount of low end tork and any other EFI'ed 350 would make a similar amount, also. The TPI is a MID RPM intake, b/c it boosts tq....right in the middle. :thumbs:
Look, you claimed that you put on SLP headers and some open exhaust and "lost low end tork". Right? That's what you typed...IDK if that is what you were actually trying to say. Your use of your car as an example is pretty worthless b/c there was no context, no data and it's unclear what you actually even have! All we really know is that you have a shitty combo with no low end torkin' exhaust combined with no top endin' TPI. The real questions I have are:
1. What did you lose low end torque compared to,
2. How much low end torque (tq from idle to ~2500) did you actually lose? and
3. What exhaust? It SOUNDS like you have SLP headers and Y pipe....and the end of the SLP Y pipe is the end of your exhaust system?
:bigears
1. What did you lose low end torque compared to,
2. How much low end torque (tq from idle to ~2500) did you actually lose? and
3. What exhaust? It SOUNDS like you have SLP headers and Y pipe....and the end of the SLP Y pipe is the end of your exhaust system?
:bigears
1) I lost low end torque compared to what it had when I had a full exhaust.
2) Can't be bothered to dyno the car to find out. But its apparent in my Dragy times compared to what it used to run at the track.
3) I already told you.
03-31-2022, 04:07 PM
#39
Supreme Member
Join Date: Oct 2000
Location: Park City, UT
Posts: 1,890
Received 272 Likes
on
190 Posts
Car: '92 Corvette
Engine: LT1
Transmission: ZF6
Axle/Gears: 3.45
Re: can i get to little backpressure
That is COMPLETELY subjective lol. The TPI system makes great power DOWN LOW right off idle because the intake flows fine because of low flow requirements. No there isn't any pulse harmonic boosts yet. The second wave harmonics kick in where you specified. That is where the TPI intake EXCELS at and BOOSTS power in that range. But nothing I said was incorrect.
Easy, objective, done. BTW, it's the 3rd harmonic. :thumbs:I already had SLP shorty 1 3/4" headers on the car with a Flowmaster single 3" cat back and a dual cat system. I rebuilt the L98 to tool around in awhile I wait on parts for my Procharged LS3 stroker (just waiting on my custom Wiseco 4.092" pistons now) so I chopped off the flowmaster system and the cats because I hated the sound and I was going to purchase a new system to use in the meantime and sell it later. Then I found out that in the 13 years this car has been sitting in my garage, no one makes a cat back system for dual cat cars anymore. So I don't even have a Y-pipe. I didn't want to spend the effort to make a custom exhaust for this car when as soon as the pistons get here, I'm focusing all my energy on the LS swap.
1) I lost low end torque compared to what it had when I had a full exhaust.
2) Can't be bothered to dyno the car to find out. But its apparent in my Dragy times compared to what it used to run at the track.
3) I already told you.
1) I lost low end torque compared to what it had when I had a full exhaust.
2) Can't be bothered to dyno the car to find out. But its apparent in my Dragy times compared to what it used to run at the track.
3) I already told you.
1. You don't actually know, because
2. Ya didn't measure SQUAT and
3. Not clearly! Sooo, it SOUNDS like, you're rinning SLP shorty's exiting the collector?
This is a waste of time. Subject, SOTP, worthless bullchit. Come back with dyno sheets.
The following users liked this post:
OrangeBird (03-31-2022)
03-31-2022, 04:21 PM
#40
Member
Re: can i get to little backpressure
I don't think anyone called anyone names so not sure what you are going on about there...
Now we're getting a little clearer picture what's going on....and the merits of you claims.
1. You don't actually know, because
2. Ya didn't measure SQUAT and
3. Not clearly! Sooo, it SOUNDS like, you're rinning SLP shorty's exiting the collector?
This is a waste of time. Subject, SOTP, worthless bullchit. Come back with dyno sheets.
1. You don't actually know, because
2. Ya didn't measure SQUAT and
3. Not clearly! Sooo, it SOUNDS like, you're rinning SLP shorty's exiting the collector?
This is a waste of time. Subject, SOTP, worthless bullchit. Come back with dyno sheets.
Drag times and trap speeds are measurements LOL. Just because they don't fit what you want doesn't require me to provide that to you. Come pay for my dyno time then bud.
And nope. Another assumption. I have the pipes that go to where the cats would be under the passenger front seat floorboard. That is where they exit right now. The collectors are next to the block. I'm sure you knew that.... LOL
03-31-2022, 05:25 PM
#41
COTM Editor
iTrader: (22)
Join Date: Mar 2001
Posts: 9,904
Likes: 0
Received 1,855 Likes
on
1,270 Posts
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: can i get to little backpressure
Removing your mid-pipe did not make your exhaust flow too much. It did change the exhaust tuning though. That's why you experienced a change in torque curve. Most the tuning effects of exhaust are in the headers, followed by extensions after the header collectors. Your Y-pipe is part of the "header extension" and the place you cut it short apparently made the engine really unhappy.
Credentials don't matter. All that matters is results and ability to explain things.
Credentials don't matter. All that matters is results and ability to explain things.
The following 2 users liked this post by QwkTrip:
OrangeBird (04-03-2022), Tom 400 CFI (04-01-2022)
04-01-2022, 09:29 AM
#42
Supreme Member
Join Date: Oct 2000
Location: Park City, UT
Posts: 1,890
Received 272 Likes
on
190 Posts
Car: '92 Corvette
Engine: LT1
Transmission: ZF6
Axle/Gears: 3.45
Re: can i get to little backpressure
^^^Someone "gets it" ^^^.
Take the RPM range, minus idle RPM, then divid the result in to 1/3's....the bottom 1/3 i s what we in the car world, call, "low end". Can you do that? Here, I'll help using a stock L98's useful RPM to try to illustrate how this works: I'll give the L98 a little "benefit of the doubt" and say that it's usable up to 5000 RPM.....fair? Good. I'll say that it's idle is ~500 RPM. Good? Good. 5000-500=4500 -useable range. 4500+/3=1500. Idle speed (~500 RPM) is your starting point, so 500+1500=2000 RPM:
500-2000 = LOW END
2000-3500=MID RANGE
3500-5000=HIGH END
This should be easy, for someone with all of you certificates!
Of course the "hard cut off" from "low" to "mid" could be debated endlessly but....^that^ should give a reasonable person a pretty good idea, of what the "Low end" range is on a stock L98.
A rebutal is not the same as a complaining. Spend a minute w/a dictionary. As for name calling;
I'm not offended but there is that gem....and then you take exception to MY "attitude"!? Wow. WOW. Way to be, my man.
1. How much time were you in the "low end" at the drag track....and how did that translate into your trap speed? :bigears. "low end, of course, being the bottom 1/3 of your usable RPM range. :yesnod:
2. I've paid for PLENTY-a-dyno session. I'd say that you can pay your own way, like a big boy. You got all those big bad ASE certs....you have money! Mostly though it's utterly laughable that you're making claims based on a car that you've made changes on and not measured in an meaningful way! If you're going to use some example....show us some actual data!! Let's see you tq (if you feel compelled to use your no-exhaust car) from idle, to 3000 RPM....w/the cats/FM in place, and w/o it! That tells the story. The ***-o-meter tells us exactly SQUAT.
I made exactly zero assumptions, about the exhaust that you have. I was actually asking, (repeatedly) or trying to clarify what you have in your car! Took what, 4 posts? And you finally managed to successfully spit it out now? So (to clarify) you currently have:
*SLP shorty headers
*Stock dual cat Y pipe, as two separate pipes back to the point where the cats WOULD be, if you had 'em. .....it sounds like. So two ~1.75" kink-bent pipes, one about 4' long? Ish? The other ~3' long? Or so? Does that sound about right?
And (again, to clarify for accuracy), you HAD, ^that, but w/the two cats, the y/joint, and then a FM 3" cat back. Is that right?
And finally, you say you SOTP lost "low end" (bottom 1/3 of the usable RPM range) by removing the FM, Y joint and cat? And you...."measured" that with your ***, and 1/4 traps on a pass where the engine was in the "low end" for how long? :bigears
Not an assumption....an attempt at clarification.
500-2000 = LOW END
2000-3500=MID RANGE
3500-5000=HIGH END
This should be easy, for someone with all of you certificates!
Of course the "hard cut off" from "low" to "mid" could be debated endlessly but....^that^ should give a reasonable person a pretty good idea, of what the "Low end" range is on a stock L98.
I'm not offended but there is that gem....and then you take exception to MY "attitude"!? Wow. WOW. Way to be, my man.
2. I've paid for PLENTY-a-dyno session. I'd say that you can pay your own way, like a big boy. You got all those big bad ASE certs....you have money!
Mostly though it's utterly laughable that you're making claims based on a car that you've made changes on and not measured in an meaningful way! If you're going to use some example....show us some actual data!! Let's see you tq (if you feel compelled to use your no-exhaust car) from idle, to 3000 RPM....w/the cats/FM in place, and w/o it! That tells the story. The ***-o-meter tells us exactly SQUAT.*SLP shorty headers
*Stock dual cat Y pipe, as two separate pipes back to the point where the cats WOULD be, if you had 'em. .....it sounds like. So two ~1.75" kink-bent pipes, one about 4' long? Ish? The other ~3' long? Or so? Does that sound about right?
And (again, to clarify for accuracy), you HAD, ^that, but w/the two cats, the y/joint, and then a FM 3" cat back. Is that right?
And finally, you say you SOTP lost "low end" (bottom 1/3 of the usable RPM range) by removing the FM, Y joint and cat? And you...."measured" that with your ***, and 1/4 traps on a pass where the engine was in the "low end" for how long? :bigears
Not an assumption....an attempt at clarification.
Last edited by Tom 400 CFI; 04-01-2022 at 09:44 AM.
The following users liked this post:
OrangeBird (04-03-2022)
04-01-2022, 10:41 AM
#43
Member
Re: can i get to little backpressure
^^^Someone "gets it" ^^^.
Take the RPM range, minus idle RPM, then divid the result in to 1/3's....the bottom 1/3 i s what we in the car world, call, "low end". Can you do that? Here, I'll help using a stock L98's useful RPM to try to illustrate how this works: I'll give the L98 a little "benefit of the doubt" and say that it's usable up to 5000 RPM.....fair? Good. I'll say that it's idle is ~500 RPM. Good? Good. 5000-500=4500 -useable range. 4500+/3=1500. Idle speed (~500 RPM) is your starting point, so 500+1500=2000 RPM:
500-2000 = LOW END
2000-3500=MID RANGE
3500-5000=HIGH END
This should be easy, for someone with all of you certificates!
Of course the "hard cut off" from "low" to "mid" could be debated endlessly but....^that^ should give a reasonable person a pretty good idea, of what the "Low end" range is on a stock L98.
Take the RPM range, minus idle RPM, then divid the result in to 1/3's....the bottom 1/3 i s what we in the car world, call, "low end". Can you do that? Here, I'll help using a stock L98's useful RPM to try to illustrate how this works: I'll give the L98 a little "benefit of the doubt" and say that it's usable up to 5000 RPM.....fair? Good. I'll say that it's idle is ~500 RPM. Good? Good. 5000-500=4500 -useable range. 4500+/3=1500. Idle speed (~500 RPM) is your starting point, so 500+1500=2000 RPM:
500-2000 = LOW END
2000-3500=MID RANGE
3500-5000=HIGH END
This should be easy, for someone with all of you certificates!
Of course the "hard cut off" from "low" to "mid" could be debated endlessly but....^that^ should give a reasonable person a pretty good idea, of what the "Low end" range is on a stock L98.
1. How much time were you in the "low end" at the drag track....and how did that translate into your trap speed? :bigears. "low end, of course, being the bottom 1/3 of your usable RPM range. :yesnod:
2. I've paid for PLENTY-a-dyno session. I'd say that you can pay your own way, like a big boy. You got all those big bad ASE certs....you have money! Mostly though it's utterly laughable that you're making claims based on a car that you've made changes on and not measured in an meaningful way! If you're going to use some example....show us some actual data!! Let's see you tq (if you feel compelled to use your no-exhaust car) from idle, to 3000 RPM....w/the cats/FM in place, and w/o it! That tells the story. The ***-o-meter tells us exactly SQUAT.
2. I've paid for PLENTY-a-dyno session. I'd say that you can pay your own way, like a big boy. You got all those big bad ASE certs....you have money!
Mostly though it's utterly laughable that you're making claims based on a car that you've made changes on and not measured in an meaningful way! If you're going to use some example....show us some actual data!! Let's see you tq (if you feel compelled to use your no-exhaust car) from idle, to 3000 RPM....w/the cats/FM in place, and w/o it! That tells the story. The ***-o-meter tells us exactly SQUAT.I made exactly zero assumptions, about the exhaust that you have. I was actually asking, (repeatedly) or trying to clarify what you have in your car! Took what, 4 posts? And you finally managed to successfully spit it out now? So (to clarify) you currently have:
*SLP shorty headers
*Stock dual cat Y pipe, as two separate pipes back to the point where the cats WOULD be, if you had 'em. .....it sounds like. So two ~1.75" kink-bent pipes, one about 4' long? Ish? The other ~3' long? Or so? Does that sound about right?
And (again, to clarify for accuracy), you HAD, ^that, but w/the two cats, the y/joint, and then a FM 3" cat back. Is that right?
And finally, you say you SOTP lost "low end" (bottom 1/3 of the usable RPM range) by removing the FM, Y joint and cat? And you...."measured" that with your ***, and 1/4 traps on a pass where the engine was in the "low end" for how long? :bigears
Not an assumption....an attempt at clarification.
*SLP shorty headers
*Stock dual cat Y pipe, as two separate pipes back to the point where the cats WOULD be, if you had 'em. .....it sounds like. So two ~1.75" kink-bent pipes, one about 4' long? Ish? The other ~3' long? Or so? Does that sound about right?
And (again, to clarify for accuracy), you HAD, ^that, but w/the two cats, the y/joint, and then a FM 3" cat back. Is that right?
And finally, you say you SOTP lost "low end" (bottom 1/3 of the usable RPM range) by removing the FM, Y joint and cat? And you...."measured" that with your ***, and 1/4 traps on a pass where the engine was in the "low end" for how long? :bigears
Not an assumption....an attempt at clarification.
Dual cat cars don't have a Y-pipe until after the cats. Therefore, I have no Y-pipe. Just one approx 20" pipe from the drivers side collector and one 16"-ish pipe from the passenger side collector. The power this car made with the cats (that were hollowed out), Y-pipe and 3" exhaust to a 3 chamber Flowmaster caused better exhaust velocity and better scavenging through the useable power range where the TPI is capable of making power (NOT SPECIFICALLY WHERE THE HARMONIC TUNING IS MOST EFFECTIVE!!) Your entire argument is based on your lack of reading comprehension and snark attitude that you think you know more than me. Pro tip: You don't.
You've been dismissed. BYE FELICIA
04-01-2022, 11:07 AM
#44
Supreme Member
Join Date: Oct 2000
Location: Park City, UT
Posts: 1,890
Received 272 Likes
on
190 Posts
Car: '92 Corvette
Engine: LT1
Transmission: ZF6
Axle/Gears: 3.45
Re: can i get to little backpressure
Except I explained that the TPI intake flows well for low end and makes good power. I already explained that the harmonic waves hit in the mid range. You explanation for what is low/mid/high end is not even needed. The entire point of my initial reply was talking about how open exhaust can shift the scavenging effect of the exhaust from where the TPI makes power (750-4750-ish RPM) to outside that range and be detrimental to overall power curves. You are literally arguing points I never made.
You've never used a Dragy have you? LOL. It literally shows you the entire acceleration curve over the entire run. More acceleration is more power. Yeah? Yeah. So its pretty easy to know where you shift gears at what speeds and know what RPM you are at and if you are generating more acceleration or less. Get with the times! This new tech is pretty nifty!
*IDK where TPI makes power,
*I've never used Dragy (or other similar apps)
*I'm not "with the times"
*I'm "assuming" what exhaust you have, when I'm actually ASKING what you have since you're so cryptic about it.
I know what Dragy is. Show us an objective metric. Show us your "low end tork" that you lost, somehow. Something other than your ***-hole, as a measuring stick. You said you lost low end tork by cutting off your cats (hacker). SHOW US.
Look up the definition of assume, please. I did no such thing.....Once again, for the reading impaired, I was trying to pull it out of you, what you actually have, and clarify.
I know. I've had them.
Obviously, if you removed the cats, the "Y" portion would be gone. I thought that was clearly understood. Thus, what you'd end up with is two ~1.75" kink-bent pipes, one about 4' long? Ish? The other ~3' long? Or so? Does that sound about right? And you've confirmed that. -other than that I was GUESSING that you had the whole pipe, to the cat (to where the cat used to be), still in place (since you never said). Now we all know; you cut 'em off, shorter....apparently at 20 and 16". Good to know. Thank you....finally.
The power this car made with the cats (that were hollowed out), Y-pipe and 3" exhaust to a 3 chamber Flowmaster caused better exhaust velocity and better scavenging through the useable power range where the TPI is capable of making power (NOT SPECIFICALLY WHERE THE HARMONIC TUNING IS MOST EFFECTIVE!!) Your entire argument is based on your lack of reading comprehension and snark attitude that you think you know more than me. Pro tip: You don't.
The reality is that there is another factor at play. You don't know what it is, and you don't know how much low end power you car gained or lost b/c you have no before and after data. If you do, SHOW IT. Removing the exhaust after the cats should have had no meaingful effect on power b/c either way, it's after your expansion point (the cats). So either you have no idea what power you're making (most likely) OR there is another factor at play such as ECM tune or something that caused an actual diff (that you can't show us).
You have a shorty header, a pair of ~2' secondary tubes. As QwkTrip stated:
You effectively chopped your "header extensions" so you MAY have traded some low end, for some top end. I'd bet it's a meaningless amount at both ends but we'll never know, since all we got from you is WAG'ing using you SOTP meter. As you were, w/your hacked up car.
Last edited by Tom 400 CFI; 04-01-2022 at 11:11 AM.
The following users liked this post:
OrangeBird (04-03-2022)
04-01-2022, 11:43 AM
#45
Member
Re: can i get too little backpressure
I don't need to prove it to you. I already provided videos explaining the phenomenon in great detail. Do you not have YouTube? I never made assumptions. You asked questions as if you didn't know. Unless you are using the Socratic method of debate, it would be really odd to ask questions of things you didn't know about LOL.
I am done here. I've proved my point. If I go on, I'll need to start charging you tuition.
I am done here. I've proved my point. If I go on, I'll need to start charging you tuition.
04-01-2022, 02:15 PM
#46
COTM Editor
iTrader: (22)
Join Date: Mar 2001
Posts: 9,904
Likes: 0
Received 1,855 Likes
on
1,270 Posts
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: can i get too little backpressure
You are both smart guys. I've concluded there is no technical disagreement here, just some sloppy choice of words being dissected and mostly a bunch of hen pecking to see who's going to be boss.
The following 5 users liked this post by QwkTrip:
Aaron R. (04-05-2022), Blown_WS6 (04-01-2022), TTOP350 (04-03-2022), ughmas (04-03-2022), Whitebird75 (04-01-2022)
04-02-2022, 06:54 AM
#47
Supreme Member
Re: can i get too little backpressure
I should have my head examined for coming into this thread.
Blown_WS6, did you adjust the timing and the fueling when you were running “open” exhaust?
Blown_WS6, did you adjust the timing and the fueling when you were running “open” exhaust?
The following 2 users liked this post by BadSS:
DynoDave43 (04-03-2022), OrangeBird (04-03-2022)
04-02-2022, 07:32 AM
#48
Member
Re: can i get too little backpressure
yes I did. I'm now running 12 degrees BTDC base timing and have my AFPR set to 48 PSI at zero vacuum. My AFR gauge reads at 11.8:1 at WOT from 1500rpm and it works up to 12.8:1 at 5000rpm. So its running much better now but I'm waiting on my EBL P4 ECM to get here in a few days so I can tune my fuel and timing maps specifically so its not so rich down low. (I have 24# injectors) My knock counts are very low on 93 octane even with the base timing that high.
04-02-2022, 08:02 AM
#49
Supreme Member
Re: can i get too little backpressure
yes I did. I'm now running 12 degrees BTDC base timing and have my AFPR set to 48 PSI at zero vacuum. My AFR gauge reads at 11.8:1 at WOT from 1500rpm and it works up to 12.8:1 at 5000rpm. So its running much better now but I'm waiting on my EBL P4 ECM to get here in a few days so I can tune my fuel and timing maps specifically so its not so rich down low. (I have 24# injectors) My knock counts are very low on 93 octane even with the base timing that high.
The reason I ask is that in over 40 years of tuning hundreds of cars I have never seen a situation where a properly tuned "uncapped" car ran worse than a full exhaust. I've installed free-flowing full exhaust systems that ran within hundredths of a second as uncapped, even with torque tubes, but I've never seen one slow down when "uncapped" - at least none I've tuned on. Seen plenty slow down with no tuning through.
The following users liked this post:
OrangeBird (04-03-2022)
04-02-2022, 09:24 AM
#50
Member
Re: can i get too little backpressure
So to clarify, is it now running as good or better with the "open" exhaust after tuning than it was before you cut off the exhaust system?
The reason I ask is that in over 40 years of tuning hundreds of cars I have never seen a situation where a properly tuned "uncapped" car ran worse than a full exhaust. I've installed free-flowing full exhaust systems that ran within hundredths of a second as uncapped, even with torque tubes, but I've never seen one slow down when "uncapped" - at least none I've tuned on. Seen plenty slow down with no tuning through.
The reason I ask is that in over 40 years of tuning hundreds of cars I have never seen a situation where a properly tuned "uncapped" car ran worse than a full exhaust. I've installed free-flowing full exhaust systems that ran within hundredths of a second as uncapped, even with torque tubes, but I've never seen one slow down when "uncapped" - at least none I've tuned on. Seen plenty slow down with no tuning through.
What I CAN say, is that there were several times throughout the cars life, that either my exhaust fell off because I didn't tighten the clamps enough, or I took the exhaust off to hollow out the cats since they clogged up from lean misfires, or I took the exhaust off because it sounded cool, and EVERY time the exhaust of off, the car was noticeably slower. It wasn't until I gained more knowledge and experience did I discover why. The why is explained in the YouTube videos I linked above from Engineering Explained. I learned it when I had to learn the curriculum for High Performance Powertrains when I was an instructor at WyoTech.
I have the car tuned well for right now despite a stock EPROM and ECM. One thing I DO know is, you can't tune out the intake runner size and exhaust scavenging characteristics. You CAN optimize for them sure, but if you had an intake and exhaust that were designed to work together and then tuned it, you will always get better results. This is objective information. It's well known and well documented. I didn't discover this and I'm surprised there are people here arguing it.