LMFAO

I have to back up my chevy man there is a thiing called "too little back pressure" rx7 should take his var to a dyno with and with out pipes on it and look at his lose in hp when he has no back because he has no backpressure, no backpressure imbalnces the motor making it not run most effecintly. a little backpressure is always good, rx7 says one thing but then argues the other end of his earlier statement in a later post......once again

LMFAO

 

I've had plenty of exhaust systems on my thirdgens and the best performance is always the middle road. Not HUGE and not small. I have the SLP tri-y headers and the intermediate pipe with gutted cat. When I first got the car the muffler was a super turbo but it was a 2.5" in so the SLP pipe had a downsize adaptor on it. I hacked off the muffler and left the 2.5" adaptor piece because I didn't have a torch. I didn't want to damage the SLP stainless i-pipe. So I did my motor swap, the 330hp crate 350 and it ran very strong. I did my own eprom tuning and it was great, the low end was a definate strong point. Keep in mind this was a brand new engine so I wasn't running the car beyond 3500rpm! I drove it like this for a few months. Then I got the adaptor removed and was running no muffler 3" pipe. Too loud but I was cheap and only drove it a few miles to and from summer job/work back roads. The car had a huge problem with low end power. It didn't want to pull until a later rpm and no, I didn't mistaken the power loss with sound. Oh yeah, and at the time I still had the 3.08 open diff auto so it was very noticable. Stock torque converter probably made a difference. Then I got the Summit 3" muffler and slapped it on for inspection. Ran much better for the street. Then I redid the eprom again until I liked it and it was great. It's much smoother in sound and operation. Somebody explain this and tell me their is no advantage of a little back pressure. BTW, I think there is such a thing as back pressure. It's a slang term for the pressure build up in the exhaust before the tip. There is a positive pressure unless you run open tubes on the exhaust ports. If I blow on a straw and put my finger on the end, I would say my finger is creating back pressure, what else would you guys say my finger was doing?
Again, shift points and gears have a lot to do with an exhaust system. If your engine has a huge cam and cubes then it wants big exhaust. A small engine like a Lg4 wouldn't be faster in the 1/4 with a massive exhaust system. The car would need a 4000+ stall converter, gears, and a cam that would require anything bigger than a 3" single exhaust! Get my drift or are people still confused. Oh yeah, and the engineering bit I through out there was just my opinion. From what I've gathered the people that understand all the physics either teach or are engineers of some sort. I would like to meet a buisness major that knows more about physics than a graduating engineer.
How many have taken a class in thermal dynamics and materials? How many people (other than engineers) can say they can build/design an efficient a/c system for a building etc.

 

You guys need to study... something....maybe not cars. The reason a car will make a little more low end torque with a system over the open headers is....... horsepower is torque x rpm. with the exaust on then the cylinders scavange better at a lower rpm therefor you get more torque, but at the cost of not so good cylinder scavanging at a higher rpm thus reducing horsepower. It also works the other way. With open headers the cylinders scavange better at higher rpms but cost low end torque. However most race engines or mod street engines will benifit from the open exaust. They make so much torque they can roast the tires off and they don't cry about loosing a couple of ft pounds of torque. They and I would rather benifit the extra horsepower up the rpm range where it will make it really zing. But remember if you don't turn your motor really high all the time then you would probably benifit from the low end torque where your motor spends most of its time. Laymens terms

 

I would just wan´t to remind you of that You can have an excaust with too good flow . Because the inlet and outlet valves are open at the same time (for a fraction of time) you can infact suck the fuelmixture out of the cylinder (the mixture that we use blowers, turbos and alike to get as much as possible off in to the cyl.). It´s not much it will effect but when you are trying to get the most out of an engine it´s one thing you have to take in consideration.

You can´t have too big excaust but you can have one with too good flow.

 

A little correction to what I just said.
The excaust will always suck some of the fuelmixture out because we have to have sucktion in the cyl. it helps sucking in the fuelmixture. But with too much flow in the exaust it sucks out too much. It´s a very fine line between too much and too little, when it´s just right you should have the maximum fuelmixture fillrate in the cyl.

Longer excaust manifolds achives better fillrate in lower rpm, therefor more power at lower rpm.
Shorter manifolds achives better fillrate in higher rpm, therefor a loss off power at lower rpm.

A adjusting excaust manifold would be the optimal thing.
Optimal torgue and optimal horsepower.

If I didn´t get it clear inaff just let me now and I will try to explain it better.

Hope you understand some off my words, I´m not the very best in english.

 

BLAH, BLAH, BLAH...To answer your original question (50 some posts later) Dual 3in on a daily driver depends on how you drive. If you drive with your head in your A$$, then of course it will not work. If you drive like you have a little since and channel your rear floorboards, it is actually not to bad. You can still run it down either side of the driveshaft, it will not hit the torque arm if done properly. I just love how people with their 14-15 second cars try to tell you what will and won't work. If you want to do it...do it, it is your car! I have dual 3in under my car...and I think it kicks A$$!

 

excuse me KDoggsPimpJetta

you must not have read this whole thread yet
I have been saying that backpressure is evil. I will still hold to that
backpressure = restriction
restriction will make the motor waste it's energy on something that it shouldn't

now as far as taking my car to the dyno without any pipes on it I would lose a lot of power all over the rpms range but why?
I talked about that already and so did a few other ppl
I would at that point not have the scavanging effect.
what is the scavanging effect you might ask?
it is when the exhaust on it's way out of the pipes leave a low pressure zone behind it that will help pull more exhaust out on the next port opening.
oh wait did I say low pressure zone? wouldn't that go against the whole backpressure idea that you say you need?
I have been saing also that when you go up to a larger pipe you are going to lose velocity which will make the gas lose there scav effect and also the gas will tend to eddy and guess what? that will CREATE backpressure

my goodness there might be hope for you yet

also if you want to say that backpressure is good why not give a reason or two as to why it would be good, rather then oh yeah you just need it. and then explain as to how you came up with that idea. I notcie you put a reason up there but can you explain why that is so?

I have been saying the whole thing the whole time I was on the post
not fighting for one side then fighting for the other
again I ask of you to READ the whole thing and maybe take a moment to understand what I am saying here
and also if you notice that your chevy man (if you are talking about chevyluva3) also put a post up saying that he agreed with us at the end so why not back that up.


so again to get to the main idea of the post
true dual 3" pipes are overkill
if you are going to do it though put a megaphone pipe as far away as you can get to expand it out to 3 inch
only reason I can see to do it would be sound or looks cause you will not gain any performance from that.

 

:sigh: I hate these posts... bare with me here...

Assume the word "backpressure" never existed and you'd all be better off...

Everything is about velocity... you put a .5 inch pipe next to the exhaust port and yeah, you're going to have alot of velocity coming out of that pipe, but because of it's small size... all the exhaust gas can't excape in time... we often call this "blockage" "backpressure"... true there is positive pressure on the leading edge of the blockage but it's all because of velocity...

now put a 4inch pipe next to the exhaust port... there is very little speed through the pipe, and it's big enough that all the gasses can excape, but it messes up the scavaging effect tuned headers have... these huge pipes mess up torque numbers because at idle the exhaust gas pulses arn't coming fast enough to keep in line with scavaging...

these are dramatisations... but I hope you get it...

The idea of tuned exhaust is to get all the gasses out of the cylinders fast enough so that it's all gone before the next pulse comes... smaller pipes create more velocity therefore getting the gasses out quicker, making them more effective at lower RPM's... bigger tubes take more time making them more effective at higher RPM's...

this same principle holds true the whole way down the exhaust tract... you open it up to a 5inch pipe and all the exhaust slows down... no velocity to carry it down the rest of the way and the rest of the gas hits this big mass of dead air... it'll eventally catch up with you, though the farther down the tract the 'dead air' is, the less effect it has...

The idea behind collectors is to time the exhaust pulses so they all come together in sequence, so the end result is a constant flow of gas...

when done in moderation it can help you, when you throw things out of proportion like I have it'll screw things up...

I hope I got that all right, and I hope that helped...

 

I'll bet chris87 is really sorry he ever ask the question about the 3" duals.

 

I enjoyed this post. It was a good debate, and for me, it cleared up my preconceived incorrect notion about "backpressure" thus helping me realize that my original restrictor plate idea (to compensate for the too big pipes) to be incorrect. I feel like I have a better understanding of exhaust technology. Of course, I'll be going with the more conventional 3" single pipe but now I know that dual 3" is not merely overkill, but it would've actually hurt my performance by CAUSING backpressure. Interesting and educational debate, thanks everyone, for your input, especially RX7Speed!!!

 

Hey bro what about me? RX7Speed wouldn't have explained it so well, without me challenging him.

 

damn right on that


good thing about debates
if nobody tries to fight it can you really explain it

 

Yeah, sorry Chevyluva! You had the same idea I did before we were both enlightened Thanks EVERYONE who participated in this debate; very helpful! ~Chris