I just did headers and exhaust on my car, put it on the dyno and am disappointed with the results.

the setup:

slp 1/34" headers with air tubes

dual 2 1/2" cats

custom, mandrel bent 3" cat(s) back

flowmaster 40 series muffler

dual 2 1/2" mandrel bent tailpipes.

"seat of the pants" feel was great, it felt much more powerful, it spins the tires where it bogged before and the g-tech times were considerably better.

however ....

put it on the dyno thursday night and only picked up 6 hp and 9 lbs ft torque. i was hoping for 20hp.

the car runs perfect. smooth idle at 650rpm, no stalling or stumbling. timing is set at 4 degrees advance .... think there may be a few more hp going to 6 or 7 degrees advance. i'm going to do some tuning and see how much more i can get.

awhile back there was a big discussion on what headers and exhaust were worth on these cars. i felt (and still do) that you wouldn't see huge gains because the heads were so restrictive and the cam was so small. got flamed pretty hard. i'm going to withhold final judgement till i do more tuning, but when i was getting hammered by guys saying headers and cat back would be worth 30+ horsepower, i said i'd shut my mouth till i'd done it and could speak from experience.

well ... helllo!

one thing i believe this does settle, though, is the big tube/torque issue. over and over people told me putting 1 3/4" primaries and dual cats on an l03 would kill the torque. the truth is, the hp and torque curves look almost exactly like they did before, just a bit higher, the gains in horsepower and torque were consistent across the rpm band, which i believe explains the wheelspin issue. i think 9 more lbs ft torque at 1500-2000 rpm is just enough to cause the "sweet spot" where the car hooks up and doesn't either bog or spin to shrink to a very small one.

i think the bottom line on header tube size is that when you're talking about a shorty header that steps down to a single exhaust, the bigger the better.

on another note, taking the hat off the stock, 84' cowl induction air cleaner was worth an additional 4 hp and 6 lbs ft. torque.

 

Thanks for the research and info!


What was the timing set at when you dynoed the car?
Also how did you get the measurements for HP and Torque, do you have a wide band O2?

 

I wonder how much gain you would see with decent heads? So what did you dyno before and after?

 

the timing was set at 4 degrees advance

the testing was done on a dynojet 248c at dynolab

http://www.dynolab.net/

arthur, the owner is a great guy. he runs a special on thurdsay nights ... 3 pulls for 50.00, but no wideband tuning.

i've used dynolab exclusively.

the baseline pulls before the exhaust mods showed a best of 164 hp and 253 lbs ft. torque.

after the headers it did a best of 170 hp and 264 ft lbs torque.

with the air cleaner top off, it did 174 hp and 270 lbs ft torque.

the only other changes were new plugs, a set of performance distributors "live wire" plug wires, a 180 degree thermostat and a 180 degree fan switch.

i plan on booking a wideband tuning session at dynolab, but first i want to get a fuel pressure gauge and my vafpr installed.

before i do the heads, i plan on doing an intake swap and seeing what that does. a number of guys on here have gotten a lot of hp and great times without changing heads or cam, and i want to see if i can, too.

when it's time for heads and cam, i don't think an 80-100hp increase is unreasonable to expect, provided all the components are matched and the tuning is dead on.

i'm going to play with the timing, etc to see if i can get more out of the combination as it is. after that, i think i need to get into chip burning. i'd planned on doing the intake before doing that, but looking at what others have gotten from it, i believe chip burning should have been my first step. someone (i believe it was dewey316) recently posted about picking up over half a second on a near-stock combo by burning better chips.

i've been afraid of it, and still am, as i'm not a great mechanic, know even less about computers, and can find no clear, step by step guidelines that i can understand. there's a tech article on burning chips, but nothing on datalogging, etc. i've read the diy-chip board and looked at craig moates' site (among others), but it's all gibberish to me.

 

Well good job and keep us informed as I have the same car minus the 5 speed and I wanna know what it can do!

 

Seems strange you only got 6hp for that mod. I wonder why you did not get more?

Conrad

 

didn't you already have a custom y pipe and exhaust before anyways so all you did was change out the exhaust manifolds.

 

it had the stock y pipe into a 3"catco cat. i thought it had a complete flowmaster cat back, but it turned out to be the stock 2 1/2" cat-back into the same flowmaster 40 series muffler i'm using now into stock tailpipes.

this exhaust should be MUCH more free flowing than the setup i had.

 

I guess I confused you with someone else, but something isn't right. Someone else put 1 3/4 slp headers on their stock L03, but he had added the tpi system and he gained like 25 rwhp I believe with no other changes. I'll have to find the graphs. If you had the stock exhaust you should have gained more than that, although 8 hp and 12 tq isnt too bad really.

 

found it. He gained 27 rwhp and 21 rwtq just from exhaust mods alone and he already had a flowmaster muffler as well. This is all with stock L03 heads and cam so that obviously isnt the problem. A lot is to be gained from exhaust mods alone as has been proven many times before, not just this guy. Something doesn't seem right.

http://bitchincamaro.no-ip.com/dyno.html

 

did you also do something to add fuel, adding headers will have a leaning effect on the motor, you want to add a little more fuel to make up for it.

 

Did you install them yourself? Maybe theres a leak somewhere. I honestly dont think tuning would have that much of an effect if headers are the only mod.

 

i haven't done anything about more fuel yet. i have a vafpr i'm getting ready to install, but wanted to get a reading on the header/exhaust install first. if it was lean, though, i'd think it'd make more power, not less. lean is fast.

cali, i did install the headers myself (with a lot of help), and had the exhaust done professionally. there are no leaks, i've been all up under the car while it's running.

 

I dont think im understanding this correctly. If he added a tpi system it wouldnt be a stock lo3. I've read the tbi-tpi swap is good for about 20 rwhp.

Did he add the tpi after the dyno run?

-chuck

 

complete oposite. your better of being 1 point rich, than 1 point lean, you being 1 point rich may cost you 5hp, being 1 point lean will cost you 20hp.

 

You read wrong. Tpi will yeild disapointing results if you expect it to add a crapload of power. Did you look at the graphs? If you did, you would have seen how he gained a combined 9 rwhp with the the tpi system, but that was also including underdrive pulleys, aluminum driveshaft, and an airfoil. Everything else was stock on the motor so it is nothing but an L03 with a tpi system on top. He gained over 3 times the amount of power with exhauast as he did by switching over to tpi and adding everything else so tpi to me is not worth it. 21 rear wheel hp is nothing to sneeze at. The stock L03 exhaust is VERY restrictive and a 6 hp gain is not the norm. Actually now that you have me started, he actually did the exact opposite with tpi that you would want to do. The torque peak went up and the hp peak went down. I think tbi would probably have made actually more hp with a better power curve that tpi.

 

Last summer I helped the nieghbor boy put TES headers and 3" edelbrock cat back on a otherwise stock LO3. We did several 0-60 runs before and after with a G-tec, and he dropped 1 full second off his 0-60.I burned him a chip with alittle more timing in it and he dropped another .2 of a second. His only other mod is a non drop open air breather. We never even touched his fuel pressure.
That was comparing a BONE STOCK exhaust to a full exhaust.

 

Maybe a little bit too much exhaust for you right now, so you didn't gain as much as other people with 1 5/8" headers. My roommate had the same problem with his LS1.

1 3/4" LTs, true dual 3", x-pipe, bullets, dump before axle.
$1200 later and only 4 hp and 3 ft*tq.

A bigger cam 224/224 .58x" and tuning got him ~50+ rwhp though.

I know it's a completely different engine, but do you see my point?

I'm thinking my 350 TPI(ported base, SLP runners) has the same problem. 1 3/4 " LTs, dual 3" cat, 3"to4" "Y", then 3" cat back. Car runs 14.2@ 99 mph with no wheel spin (2.0 60') or missed shifts. I'm thinking a lot of low end torque not quite there, due to the exhaust being too large for my engine NA.

 

i agree with beast5spd
it could be to much for you car
i have 84 chevy truck with 305, 1 5/8 headers, 2.5" in dual exhaust with h pipe nad 40 series mufflers, and I got next to nothing in the speed department either, to little backpressure i guess,
but after you add intake i would expect a big gain
matt

 

I really like this thread. I have a full exhaust, Hooker 2055s to supercomp catback... I also have a straight pipe in place of the cat. I can definitely feel more power over stock, but that's not the subject in question.

Even so, if you only gained 5-10 peak horsepower, odds are you've gained a lot more in the low rpm where it's needed. My guess is that you spin that engine up much faster than before- I know I can. Plus theres a definite change in the torque curve. I have an L03/700r4 and I can break my 2.73 open loose in second at 20-25 mph... Doesn't seem too hard right? Try it on a stock L03 haha.

Dyno numbers don't always mean everything. They're just fun to talk about. What really matters is performance on the street.

 

actually, the curves are almost identical, the new one is just slightly higher.

i'm getting ready to install a fuel pressure gauge. maybe that's the problem ... not enough fp.

i'm also wondering about the oxygen sensor. i assumed i'd need to go to a heated "3-wire" sensor, so i just reinstalled the old sensor to see if it'd run. i was surprised to see that the car runs well. however, there are a few odd things going on.

when i first start the car after it's been sitting for awhile, it idles at 1,500 rpm, slowly going down as the car warms up. i give it a 2 minute warmup every time i start it. at the end of that time, it's usually idling at around 1,000 rpm. after a few minutes driving, it'll eventually settle down to 650, 700 rpm at idle. i'd assumed that the free-er flowing exhaust and coated headers were causing the 02 sensor to take longer to heat up, causing the car to stay in open loop longer. however ....

when driving, even after running the car for hours, it's slow to come down to idle after i stop. significantly slower than before. i'm wondering if the ecm isn't getting good info from the 02 sensor. if that's the case, it'd cause the mixture to be off throughout the entire rpm range, wouldn't it?

 

beast,

you may be right, but i honestly don't think so. here's my thinking:

1. the 1 5/8" vs 1 3/4" primary debate began years ago, and centered around tuned, equal-length, long-tube headers. shorty headers are unequal length, and don't flow nearly as well as long-tubes.

2. long tube headers generally have 3" collectors. my slps have 2 1/2" collectors.

3. my exhaust "y"s into a 3" intermediate pipe. according to dave at random technology, that 3" pipe flows about as much air as dual 2 1/4" pipes would. most factory dual exhausts were dual 2 1/4" setups. the first thing hot rodders did was go to dual 2 1/2".

4. most importantly, the difference between 1 5/8" primaries and 1 3/4" primaries is supposed to be torque, not hp. while the increase wasn't what i would've liked to have seen, my torque was up all through the rpm range.

i'm thinking i may have a fuel pressure or 02 sensor problem, or the air intake may be so restrictive that improving exhaust may not help. another area i want to look at is timing. on my last dyno pull before i did the exaust, the difference between 0 degrees initial timing and 7 degrees initial timing was 15 hp and 17 lbs. ft. torque. i was at 4 degrees advance for this run.


and as far as your car goes, that lack of bottom end torque may be a blessing. my whole reason for running the larger exhaust was because i wanted to move the torque curve up a bit in the rpm range. it's been my experience that too much torque under 2500 rpm does nothing but send street tires up in smoke.

my last fast car was a 70 chevelle with a 400sbc, turbo 350 and 3.31 gears. despite the small gear, i couldn't get the car to hook up. swapping from 1 5/8" to 1 3/4" headers and a dual-plane to a single plane intake took me from 12.80s to 12.60s on horsepower. The improvement was all in the launch. suddenly, the car hooked up! prior to the change, i had to wait till the car was off the concrete pad to hit the nitrous. after the change, i could hit it from the gate. went from 12.20s to 11.70s on the nitrous.

i wish i had your 60' times! my car only runs 15.90s, yet the best 60' times i can muster are 2.30s. part of the problem is the suspension, which is set up for handline, but i believe another part of it is that most of what little power my poor old l03 makes is confined to bottom end torque.

 

Your exhaust system is a good performance exhaust system. It will serve you well in the future. It just won't serve you well for your current mods. That exhaust system isn't well matched to your car. Yes, it is too big to produce optimal results. But, who cares about optimal results when you put a great performance exhaust system on a non-performance motor?. PLEASE don't take that in a negative way. What I mean is that you have tons of things left to do to your F-Body. You currently have a small V8 with crappy heads, crappy cam, crappy intak, crappy injection, etc. That setup doesn't need or warrant the exhaust system you have. HOWEVER, with new modifications your exhaust system will begin to shine and give you more power per modification. I know guys running an extremely similar exhaust system that are in the 11's naturally aspirated. Heck, I ran 12.2's with 1-5/8" headers (when I had them). You don't need your current exhaust system for a low revving 15 second car. Whoever said that a full exhaust on a stock TBI is worth 25rwhp is just plain stupid. That's a fact. The posted link claiming 25rwhp is so blatantly wrong it made me laugh as soon as I looked at it.

Take your time and don't worry about how your exhaust didn't perform that well. Trust me, it will eventually shine in it's own right. It's a good choice and well worth it. A better header combo for your car would have been 1-1/2" headers. But, why waste money on 1-1/2" headers when you'll eventually need to replace them with the 1-3/4" ones? You did good.

Tim

 

Whoever said that a full exhaust on a stock TBI is worth 25rwhp is just plain stupid. That's a fact. The posted link claiming 25rwhp is so blatantly wrong it made me laugh as soon as I looked at it.

A dyno graph is wrong? Are all the rest of the dyno graphs wrong too that prove it? Ask Beast what he gained on the dyno with full exhaust on an otherwise stock 305 tbi. He has dyno graphs to prove it as well. I am not wrong, nor is it funny that the fact is a 305 tbi can gain upwards of 20-30 rwhp with just exhaust mods alone. This is not debatable, it is a proven fact, as show on several dyno graphs. What is funny though is you claiming a dyno graph to be wrong.

 

tim,

my plan was always to build the exhaust for the future. i didn't want to do it twice.

while i never agreed with the people saying i'd get 30-40 hp out of headers and exhaust on an l03, i was hoping for 15, maybe 20.

i'm actually pleased that the 1 3/4" headers didn't hurt my torque. even at 2,000 rpm, it's up, not down. as far as i'm concerned, that settles a major argument against 1 3/4" headers on an lo3. perhaps 1 5/8" or even 1 1/2" primaries would have givem me better torque increases, but the car spins now. more bottom end torque would only make that worse. in my opinion, 1 3/4" is definitely the way to go.

i'm going to go back on the dyno and try different timing settings after i look at the fuel pressure. i'm probably going to put a 3 wire heated 02 sensor on too, just to be sure. honestly, i'll be pleased if i can get a 15hp increase over where it was before i did the exhaust. i really don't think i'll see major hp gains till i do the heads, but i want to do one mod at a time and see how much hp/et improvement i get from each.

the next step is going to be chip burning. i was going to wait to get into that till after i did intake, heads, then cam, but i saw where dewey316 got over half a second's improvement with chip burning only. the order for the rest of the mods is:

1. chip burning

2. power pulleys

3. intake (weiand 7525)

4. heads (ported 081s)

5. cam (whatever the head flow numbers dictate)

 

I never said that. In fact, I never gave a reason for why I said what I said so stop twisting my words into something that's rediculous.

Tim

 

where is this graph with a 25rwhp increas with JUST headers.

i see one that compares.

March underdrive Pullies, air foil, aluminum drive shaft, and SLP cold air intake

to a baseline run. but no where do i see a header to no header comparions.

the closest i see is a stock exaust vs slp headers and cutout.

he gains what looks to be:

8.4 hp and 13.3 tq

 

you aren't reading it right. The numbers you quoted are comparing the cutout open vs closed. The graph above compares the stock exhaust with a flowmaster muffler to slp 1 3/4 headers and slp catback. 27 rwhp gain with the cutout open.

 

The key to the LO3 is timing! I am currently running 10 psi of boost and have my timing advanced 12 degrees. These motors love more timing!

MD

 

Dewey got 1/2 second w/ just chip burning alone?? How and when?

 

actualy with no real mods, i did much better than 1/2 a second. part of it was driver learning, but here is how my summer went.

1st time to track, untouched LO3. best run of the night was 17.1 @ 84mph

2nd Time to track. still untouched, ran a 16.6 @ 85 (notice no significant change in MPH, but i was a better driver )

3nd time started getting into tuning, didn't know much, advanced timing 4* and that was about it. 16.1@87 (i was starting to feel better, but i wanted to go 15's!)

4th time, worked on VE tables, got them closer, still running 4* of timing. ran a 16.03 @ 87 mph (yeah i about cried, i wanted that 15 sec run)

5th time, worked quite a bit on all VE tables, now running 6* of timing advance, and i started cleaning up the stock timing table. i also did a bit of WOT tuning, and got my o2mv's down from the 950+ range, to the 850-900 range. i also did some minor tweaks and added a fan switch, to keep my AIT's down. like this i ran 15.5 @ 90mph

basicly, nothing really got touched on the car, the fan switch and chip tuning were all that i did.

last weekend i put on headers, i need to get some more tuning done with that, but i am going up on the dyno in mid. jan. so i will have numbers of what an LO3 with headers, and custom chip can do on the dyno.

 

ummmm .... what language is that, french?

 

Translate: Tuning and good driving (even when stock) go a tremendous way.

 

translation.

added timing.

corrected fuel.

at WOT i was very rich (950mv or more)

so i leaned it out to a better more happy place (850-900mv range)

the IAT stuff is intake air temp. basicly i added the fan switch, and and tried (not sure how successfully) to try to route some cold air towards the intake.