hey i was wondering how much hp and tq does our cars bring stock to the flywheel and to the wheels and whats my total hp & tq with my mods in my sig

 

the stock tbi out of the factory was 170 hp about 230 foot lbs of torque with the mods you have your probably pushing 180-185 hp again these motors were never ment to be performance motors, espicially with the highly restrictive tbi setup!

 

Actually the L03 makes 170 hp and 255 tq. The tbi is not even close to being a restriction on the L03. With your mods I would say you have a little more than 200 hp at the fly and I would guess you might be able to put down between 160-170 rwhp.

 

so the 170/250 it to the flywheel or the wheels?

 

I have a 91 305tbi with open element and open exhaust (not by choice, exhaust was rusted from the catback so i pulled it) and i got it dynoed to see hp before i modded and at the wheels it put down 154 hp and 253 torque.

 

no way those mods are worth 30 hp. the heads themselves are the big restriction point on the l03, that's why you'll see people do the basic hot rod mods (headers, exhaust, ignition, intake, etc.) and not pick up much. also, increasing airflow without increasing fuelflow can actually hurt a fuel-injected car. if you look at the people who really get horsepower out of l03s WITHOUT swapping the heads, it's the careful tuners who keep the air/fuel ratio balanced.

and 91redrs, the 170hp number is the factory rating at the flywheel. when you put a car on a chassis dyno, you get rear wheel hp, generally 10-20% lower than flywheel hp due to parasitic power loss from the drivetrain.

i got my car dynod back in may. 161hp and 253 lbs. ft. torque

 

180 RWHP is doable with out changing the heads or cam. Last year I dynoed 181 with just Hooker shorty headers, 3" exhaust, open air element, and advancing the timing. I still had the AC and AIR pump on.

 

When I got my car dynoed I got 93HP and 204TQ . I have come to believe that fuel pump is going bad....

 

don't feel too bad, i only got 110hp, 260lb/ft, lol, i had a clogged cat, so i just couldn't spin the RPM's need to get the HP number up, i was pretty impressed with the 260 to the rear tires though!!!!

 

If I could find the article in some magazine where they took a stock 145 hp LG4, which btw came with the same manifolds and exhaust as our cars do, I could show you how they gained over 50 fwhp just by swapping to long tube headers and mufflers. Our stock manifolds are restrictive as hell! I believe there was another member on this board who picked up around 12 rwhp on the dyno just by swapping to the stock tpi manifolds and y pipe, so I would say a set of headers could easily put you around 200 or so flywheel hp, not to mention his other mods. Correct the heads are a big restriction, but simple bolt ons can net huge gains on the L03!

 

Flywheel.

 

i'm not trying to be a jerk, but i disagree. first, there's a huge performance difference between long tube and short tube headers. second, and more importantly, the swirl-port heads on the lo3 could quite possibly be the worst heads gm ever put on a v8 engine. you see it with people on here, you see it in magazine after magazine buildup (the few that have been done on l03's, that is) .... the heads kill the engine.

i believe it was pablo, i can't be sure, but someone on here actually got low, low 14s out of a stock short-block, stock head l03 (i believe it even had the stock cam, i could be wrong), but it was with meticulous, careful tuning.

my point was there's no way you'll see a 30hp increase with just headers, exhaust and ignition. as soon as you free up the exhaust flow, the motor will go lean.

 

I don't think you're a jerk, but I do disagree. 30 flywheel hp with headers is easy, very easy. If you can get 12 RWHP just by switching to tpi manifolds and y pipe on a stock 305 tbi, then why don't you think 30 flywheel hp with headers on back is impossible? Can you also explain the awesome results people get at the track from simple exhaust mods on our cars? PLenty of people have dropped .3 or more just with exhaust mods alone and that shows atleast a 30 hp increase. The fact that our heads are restrictive are true, but it's also true that the stock exhaust can't even support the poor flow of them. A member here dynoed his 305 tbi with only edelbrock headers and hooker catback i believe and put down 178 rwhp. Thats about 210 flywheel hp so there you go. That was also without even messing with the fuel pressure or anything and he was running pretty rich too. These cars come pretty rich from the factory, and just leaning them out can show gains.

 

I think Beast5spdGTA concluded that the stock lo3 heads were definitely a big restriction but that the stock exhaust and stock cam and intake were bigger restrictions. He ran full exhaust, L98 cam, and an aftermarket intake. I believe those were his only mods besides 3.73 gears and posi and he ran a 14.3 I believe, so that alone shows how much power can be gained without replacing the heads.

 

there's two points i'm trying to make.

1) you won't get 30 hp because the headers, while freeing up the exhaust some, still don't solve the issue of the terrible heads. you DON'T see people bolting on headers and picking up that may hp on l03s. how many third gens do you see with all the standard hot rod mods (exhaust, headers, intake, induction) that only run low 15s. it's the heads and the tuning.

to get that hp, you also have to address #2, which is:

2) you won't get 30 hp because when you put the headers and free flowing exhaust on, you make the engine flow more air without causing a corresponding increase in the flow of fuel. the engine will go lean.

in order to get the hp gain, you'd have to increase fuel flow with bigger injectors/increased fuel pressure AND careful tuning in the form of chip burning or using an adjustable fuel pressure regulator to keep the engine at the optimal air/fuel ratio.

THAT'S where the power comes from.

my car is a perfect example. 170 flywheel hp at the factory. figure 10% drivetrain loss for a manual trans = 153 @ the rear wheels. look at the mods in my sig. i get 161 rwhp. that's 8 more than stock. also, since the mods i have improve airflow and no fuel flow, my car is seriously (maybe dangerously)lean.

i'm getting ready to put in a dual cat slp 1 3/4" header setup with random technologies cats. i'll bet my *** it's not worth more than another 10 hp ... 15 tops.

HOWEVER, i ordered a complete vacuum adjustable fuel pressure regulator setup from top down solutions the other day. when that's installed and the car is dyno tuned with a wideband o2 sensor, i'll bet there's at least another 20 hp there. THAT'S how you get 200+ rwhp out of a stock headed tbi.

the point i've been trying to make is that you won't see big hp gains just by bolting things on. tbi is incredibly sensitive to air/fuel ratio. it's all in the tuning.

 

seanof30306,
What your not excepting is that it's been done, more than once. As I posted earlier. 181 rear wheel horse power with the following mods:

Hooker shorty headers
3" Cat
3" Hooker super-comp cat-back
Open eliment air cleaner.
Inital timming set to 8 degrees.
MSD Blaster coil
MSD cap and rotor
MSD 8.5 wires
New Autolite plugs

The TBI was unmodified
stock intake
stock heads
stock cam
stock prom chip

 

i surrender

 

Thank you sean made good points, but like I said the stock exhaust is absolute garbage and isnt even capable of flowing out what the crappy heads can flow in. Also the point you seemed to not acknowledge is that these cars do infact come rich already from the factory. Is there a reason why you would go with 1 3/4 headers? Engine swap in the future?

 

even with the 305, if you get over 275-300 lbs ft torque, you can end up with so much off-idle torque you do nothing but spin the wheels ... especially with a manual trans. years ago, hot rod magazine got 300hp out of a 305, but never got great track times out of it because it wouldn't hook up.

i love torquey engines for the street, but too much at the low end hurts more than it helps. big-tube headers and a single plane intake cut just a bit of that off. if they end up taking too much off, you can get some of it back by putting a slightly more restrictive catalytic converter back in.

how about that ... a cat that helps?

 

but a cat is going to hurt hi-end exaust flow more than off idle

there is something to be said for getting the right size header primary tubes, for the HP, and RPM range you want your power at. but really power is power, why would any of us do anything to ruin that. if you have problems hooking up all that torque, do some suspension mods, don't DE-TUNE the engine.

 

you frequently see street engines losing all their bottom end torque because the exhaust doesn't make enough back pressure. open headers are great for full throttle operation, for example, but you lose all your throttle response. that's why nascar cars and road racers run 3 1/2" pipes off the headers. they could easily go 4 or 5", but you need some back pressure to make torque.

i'm not suggesting the cat is a good solution, but i'd rather run big tube headers and find i need to add back pressure to improve torque than run small tube headers and find it won't hook up, and adding a more restrictive cat is cheaper than adding a more restrictive muffler

as far as suspension mods go, my car is going to remain a daily driver that i drive to the track, run, than drive home. it's also going to handle. no unhooking the sway bar, no 90/10 front shocks, no slicks or drag radials. that's going to require careful planning and tuning, cause there's no way you can do enough suspension mods under those restrictions.

i've had two 11 second street cars that i drove to the track under those circumstances (to be fair, they were low 12 second cars without nitrous). to do that, every component had to be in perfect balance to find the right compromises.

 

following up ... power is not power, unless you live at wide open throttle. causing a 3,000+ car to move is what we're doing. power is the single most important part of the equation, but not all.

an example that occurs to me: my best friend and i both had chevelles. mine was a 70, his a 72. essentially identical.

we came across a deal on two 400 sbc engines and bought them. for the hell of it, we decided to build them identically, then see who could tune theirs to be faster.

same heads (350, 300hp), same cam (engle 5.10 lift, 3.10 duration), same gears (3.31), etc.

my car was consistently 4 - 5 10ths faster. drove him crazy. not only would my car hook up off the line where his wouldn't, but it drove away on the high end, too.

we finally figured out the only differences were my big tube headers and single plane intake versus his small tube headers and dual plane. we swapped intakes ... he picked up a 10th, i dropped about half a tenth. we swapped out out 2 1/4" outlet mufflers for 3" outlets and he picked up close to 2 tenths, all off the line, because he could finally hook up. i actually ended up going back to the 2 1/4" outlet mufflers ... my car launched much harder with them.

we didn't have access to a dyno back then, so i don't have hard numbers. we knew going in those 400s were going to be torque monsters, that's why we went with the 3,10 duration cams ... to cut enough off idle torque so they'd launch with street tires. what we learned was the cams weren't enough .... my car was faster because the big tube headers and single plane intake made less bottom end than his small tube headers and dual plane intake .... more USEABLE power; i could launch and he couldn't.

also, i was faster with the MORE restrictive exhaust.

 

well, reply time. this time instead of a i did this, he did that expample, i will stick to physics.

restrictions = loss of power (torque or HP, whichever you want to think of, since HP is really just a measurement of torque). were this huge misconception of back pressure being needed started, i have no idea. but, it couldn't be further from the truth. back pressure is BAD, no matter what, not matter when. like i said, there is something to be said for running a set of tuned headers (meaning, the rigth size/length, for the amount of power you are going to make and the RPM you want to run). of course a single plane with large tubes, vs a dual-plane with small tubes, is going to make diffrent power bands, even with the same cam/head comobo. and your right, int he 1/4 traction really helps. but i still think that if you are making the power already, don't spend money to make less, spend money putting it to the ground. but anyway, back to the topic at hand.... 1 3/4" headers on a 305, are going to allow the engine to breath better at hi-revs, and to lose some low end, but it has nothing to do with back-pressure as you are thinking, it has to do with the exaust velocity, and the only reason i even comented, is because you told him to put a cat on to gain torque. that is what should be done instead, is to buy the correct size headers to start with. 1 5/8" headers with no cat, is going to better at ALL rpms, vs 1 3/4" with a cat. because with the cat, no matter what you are going to create back pressure.

personaly i think you rwhole concept of buying oversized headers, and then adding a cat to create back pressure, is crazy.

 

1 3/4 primaries for your car will be too much. You won't gain anything over 1 5/8, but you will lose everywhere compared to 1 5/8 headers.

 

1. i didn't tell him to put a cat on to gain torque. i told him to put a cat on to increase back pressure if the big tube headers cut too much torque. he could accomplish the same thing by putting on a smaller muffler and/or tailpipes, but the cat would be cheaper. it is all about exhaust velocity, and you can have too much. the smaller cat would accomplish the exact same thing as the smaller diameter headers ... slow down the exhaust velocity. the point is, if you put small tube headers on the car and have too much low-end torque, the only choice is to swap to big tube headers. if you put big tubes on it and lose too much bottom end torque, there are any number of ways to decrease exhaust velocity less expensively than changing out the headers. if your theory were correct, then the most efficient/power building exhaust would be none at all ... direct exit from the head. that has the least restriction possible. there's a reason people run tuned headers ... to find the correct exhaust velocity to give them the desired hp/torque powerband.

2. i'm never going to suggest no cat at all. the car won't pass emissions without a cat.

3. i'm done responding to you. you want to disagree with me, fine. you want to make personal attacks, forget you. i'm confident that i know what i'm talking about. i've pulled out my checkbook, skinned my knuckles and gone to the track to prove my theories many times over.

 

Any time you increase backpressure you lose torque and horsepower. Thats just stupid. So what ure telling him is if the large tube primary headers cause him to lose torque to increase backpressure to bring it back up? Ahahahahahaha. All that will do is cause him to further lose torque AND horsepower. You really shouldn't be so confident about these things sometimes. You say if you have "too much torque" the only way to remedy this is to put on larger headers, yet you say if you dont have enough, there are several ways to get it back? WTF? If you spin off the line you need better tires or suspension or just plain learn how to drive. You can never have too much power. Also, the most efficient exhaust would be none at all, but you just can't due that because the fire coming out of the heads would pretty much destroy everything. The whole reason we have headers is to direct the flames and hot gasses away from the things we don't want to damage. The are cars that can direct thier headers any way they want and they choose to send it out of the heads as smoothly and without any restriction at all. They are known as top fuel and funny cars.

 

i'm setting my car up for the 400 sbc i plan on putting in eventually. i'll definitely need big tubes for that engine.

i still believe, however, that they could be useful on a 305.

in an earlier post, i mentioned a series of articles hot rod did back in 1989. they took a 305 5speed camaro, kept the stock short block and made over 300 hp, 300 lbs ft torque. they could never get it to hook up, which kept it in the low 14s when they'd hoped for mid 13s.

this is my first experience with fuel injection, so i've tried to learn as much as i could before i started making changes. i ran down the guy who did the work on that hot rod camaro, chris kelly, who is now the chief of engine development for calloway corvettes. he was good enough to talk to me about the project, he even gave me a tbi/carb adapter they'd developed for the project. he told me after thrashing the car for as long as they could and still not being able to get it to hook up, they'd wanted to swap out the intake for a single plane and the headers for big tubes to move the torque curve up in the rpm band, but chevrolet wanted the car back so they never got to do it.

i agree, bolting a set of big tubes onto a nearly stock 305 is overkill, but i plan on swapping on a set of vortecs and changing cams and intakes on the 305 before i swap engines. i think the 305 will need that breathing. the bottom line is there's only one way to find out ... do it. the difference between this and other cars i've built is that i'm doing everything in stages and i'm dynoing it after every change, so i'll be able to quantify everything i do.

 

i'm sorry, what times are YOU running?

one of the ways you increase torque, or at least move your torque curve lower in the power band is to decrease exhaust velocity. you do that by increasing back pressure. you essentially said that yourself when you said 1 5/8" headers were better for my application, that 1 3/4" primaries would be too much. if that's correct, the reason 1 3/4" headers would be too much is that their larger size reduces back pressure and increases exhaust velocity, causing the torque curve to move up in the power band.

jesus, before you flame somebody, know what you're talking about. john lingenfelter's book on small block chevys is considered the bible on small block power ... he does a whole chapter on exhaust and how you use intake and exhaust velocity to tune your torque curve. look into it.

on a street car set up to handle as well as go fast in a straight line without slicks or drag radials, you absolutely CAN have too much power. i stopped being impressed by huge clouds of tire smoke a long time ago.

 

Only low 11's Man, quit being an ***. You have been proven wrong on everything you have said today. First you say it is impossible to increase hp on an L03 with headers because the heads are too restrictive. Then someone posts actual dyno results with only exhaust mods with an increase of almost 50 flywheel hp ON A STOCK L03. Now you are proven wrong once again with yout little theories and physics that are all wrong. You have been owned so be quiet. You will only make yourself look worse.

 

its a l03

the intake is restrictive.
the exhaust is restrictive.
the cam is restrictive.
the heads is restrictive.
the valves are tiny and restrictive.
and the bore shrouds the valves


it all around is a low performance motor. EVERYTHING needs to be tweaked to improve it...........

and even then, its a still a 305 bore.

just because there is a restriction before that point in the airflow of the motor, doesnt mean that opening up the restriction after it wont help. esp with thoes log manifolds. dude, you would prob get a performance increase going to the old school ram manifolds compared to thoes.. lmao....

 

low 11s. right. you don't know that torque is directly related to backpressure and you're runnig low 11s.

nice.

 

Yeap, if you would like the specs on my engine I would be glad to give them to you, but from the looks of it you probably wouldn't understand any of it anyways so I wont. An engine is basically a giant pump. It pulls in air and fuel and pushes out the byproduct of the 2 when ignited. Any time you put more backpressure in the exhaust of an engine, you are making it work harder to push the exhaust gasses out of the ports in the heads. When you relieve this backpressure, the engine doesn't have to work as hard so you increase both horsepower AND torque. The whole torque issue is an old wives tale that you obviously believe to be true. It is not! If you think increasing backpressure will in any way create more torque you are mistaken. Headers were designed to carry the flames and hot gasses away from the engine so that things dont get damaged. You want that path to be as smooth as possible so that the engine doesn't have to do extra work to push it out. By opening up the exhaust you let the engine breath better there for creating more horsepower AND torque. You can go too big though, which effectively slows down the escaping gasses, and in turn creates backpressure again. Think of it as a garden hose. When you turn the hose on a lot of water comes out, but at a very slow rate. If you put your thumb over the end of the hose the water comes out very quickly, but if you restrict it too much, not very much water comes out. The same thing applies to exhaust gas velocity. You want to match your exhaust to your engine and any engine that has less than 300 hp can't possible produce enough gasses to require large primary headers or exhaust pipes. All you will be doing is slowing down the escaping gasses and hurting the engine more than helping it. With the stock manifolds though, it restrics the flow of gasses so much that the engine has to work a lot harder to push them out of such a small space and you lose hp. It's all about matching your components to you engine.

 

its not backPRESSURE...... its the frequency of the pulse sent back towards the exhaust valve.


think of it this way..

we all know know when the intake valve closes, it puts a pulse backwards across the intake... and by changing the length of the runner, we get the echo, or return of that pulse time just right in a specific RPM range to help push more fuel into the cyl...



now... imagine a pulse timed so that it helped scavenge the exhaust.... or it helped hold the intake charge in the cyl when you have a cam with a large overlap....

just realize that its not back PRESSURE but the pulsing wave thats doing that..... its not a constant back pressure..

now if you put a piece of metal in the pipe, while widing the pipe, it would flow the same, yet allow that pulse to bounce back.... that is how some race mufflers help with power... they dont create back pressure but they use the pulse to help make more power....




and if that didnt make sence, its almost 5am, so bite me......

 

dude,

matching components is what i've been saying since the beginning of this thread.

you hammered me on the headers being put on and the guy getting 50 hp. i still don't buy it, but i'm just going to back off on that one till i put my headers on and dyno the car.

i never said it wouldn't make the power anyway. i said it wouldn't make that much power just by bolting the headers on. i said you have to MATCH COMPONENTS, that causing the engine to flow more air without causing the engine to flow more fuel would throw the air/fuel ratio off, cause the engine to go lean and minimize hp gains. i said the only way to get that kind of horsepower with a header swap was with careful tuning. go back and read it.

all my car has is ultimate tbi mods, a random technologies cat and a flowmaster cat back setup and it was so lean it couldn't pass emissions. i thought it would be a problem, as the plugs were clearly showing a lean condition, and i ended up havong to shim the spring in the fuel pressure regulator to richen it up enough to pass.

i just dynod the car at 161 hp. i'm putting on a vaccum adjustable fuel pressure regulator before i put the headers on and am going to dyno it again before i do. bet my bottom dollar there's another 10 hp there just in tuning the fuel pressure.

when i put the headers on, even with careful tuning, i don't think i'll see any more than 190 rwhp with the stock intake, and i'll bet i'm going to have to work like hell to get that with timing and fuel pressure adjustments. without tuning on a dyno with a wideband 02 sensor, i don't think anyone but a tuning genius could get that sort of an increase on these cars with just exhaust mods.

when i've actually done it on my car, i'll say it again.

as far as the torque issue being an old wive's tail, i must be an old wife, then, because i've absolutely tuned an exhaust system to move the torque curve up or down in the rpm range.

when the exhaust gas can't escape, it reflects back, causing a scavenging effect. that's the whole idea behind "tuned" headers. they control that reflection. same with a borla muffler. it's not just the sound you're making adjustments to. by the way, that reflection is backpressure, which is quite different than restriction.

i essentially agree with you on the "under 300hp" issue, although the number is probably lower. my flowmaster is a 3" in, 2 1/2" out system. with the 1 3/4" headers, i believe i'd lose serious bottom end if i went with a bigger exhaust system. when the 400 goes in, however, that'll be an issue.

the cam is a big part of the equation, too. lt1s and lt4s are not known as torque monsters. using those cams won't cause the kind of problems i'm talking about.

i still say it's easier and cheaper to advance or retard the cam or tune the exhaust than it is to spend the money and go through the grief of swapping headers if the small tube headers won't do the job.

when i get the swap done, i'll post the numbers. till then, i'm done on the subject.

 

wow, i missed this all last night. i am not going to reply to ALL of this, but here is a bit of replies to some of the things that are VERY wrong.

1) Torque is directly related to LACK of back pressure. backpressure = pumping loss. ALWAYS. period. it is physical law, just like gravity. the reason 1 5/8" headers make more torque at a lower RPM is because a smaller tube creates higher velocity. but has a limit to how much flow it can handle. 1 3/4" headers have such low velocity with low amounts of exaust gas going through them, that the gases slow down, and CAUSE backpressue, and thus a loss of torque.

2)"when the exhaust gas can't escape, it reflects back, causing a scavenging effect."

no that is reversion, which is a bad thing. scavenging effect, is the low pressure area behind an exaust pulse, that low pressure area actuly sucks the exaust out of the next opening cyl.

3)"if your theory were correct, then the most efficient/power building exhaust would be none at all"

did i say that? who was the who mentioned tuned headers? with out the headers you dont' get the benifits of scavenging.

4) "you want to make personal attacks"

i am sorry, i don't see where i ever attacked you, i disagree with you, and i am going to point out what i see as errors. but i never called you a name, i never said anything about YOU.

now i am done, this argument has been done too many times. and really i am not going to argue anymore about it. you are making claims that lingenfelter (in a book) told you backpressure was good, ect. if he was in a condition to respond, i would ask you to call LPE, ask for John, and ask him if backpressure makes torque. hell, call any good engine build and talk to them. i can provide you with some phone numbersr of very reputable builders. no one who understands how an engine works, is ever going to think that backpressure=power. like i said, it is a physical impossibility. now really, you are starting to make yourself look bad, before you respond again, i would like you to sight actualy proof. because if i respond again, it will not be my opinion, it will be with physics equations (i doubt you will be able to follow them, or understand them, but they will be there) .

 

I pretty much agree with you, except I dont see how you can not believe something when it has been proven more than once already. It seems that with exhaust mods alone, most people will see around 180 rwhp, give or take a few, with a manual trans 305 tbi. The lean issue I find suprising, because most people find their cars to be pretty rich with the stock fuel pressure when hooked up to a wide band. I agree that proper tuning is the only way to really get the most out of your car, but when others have gained close to 50 flywheel hp with only exhaust mods on an otherwise stock 305 tbi on the dyno, you really can't argue with it.