04 GT Dyno results :(

[rickisrad]

I have a 2004 Grand Prix GT Naturally aspirated 3.8. I took it to get a Dyno test done today and was VERY unhappy with the results. I ran a max power of 155.2 and torque of 185.7 my air fuel ratio was very good it stayed at around 13. I thought that I would run way higher than this.

The engine modifications I have are a front powerlog, ceramic coated crossover pipe, 2.5 zzp downpipe w/high flow cat, 2.5 inch exhaust cat back with 40 series flowmasters, ZZP 1.0 PCM, cold air intake, 10.3 mm zzp wires w/ autolite xp iridium 606 plugs, voltage booster, alternator rewire, fuel pump rewire, 180 degree thermostat.

Any help on what I should be running with these mods will be greatly appreciated!!!!!! Any input on whay may be causing these low numbers would be great> The only 2 things I can think of that is holding me back is that I should maybe look into the ignition system, maybe MSD coil packs and the y split on my custom exhaust is way too small (around 1 7/8) by the muffler split.

[drdisque]

What brand dyno is that? I can't tell from the sheet.

Also, I know the 3.8 is a torque happy engine, but peak torque seems to come on awfully low, you might be having the backpressure issue you suspect.

You might also want to look at something to tune your spark timing and find some power there.

[rickisrad]

It is a Dyno Jet. I am going to fabricate something to get rid of the backpressure. I will put the MSD coil packs on there to try and help with spark. I should have took my o/e wires and did a run with them to see if the 10.3 wires were causing an issue.


Thanks, any other suggestions would be helpful.

[BNaylor]

What are your realworld track times? 1/4 ET?

That does seems low for wheel HP and torque for a NA SIII 3800 engine but nothing in your mods are significant enough to offset anything for a NA SIII 3800 engine.

The MSD coils will be a waste of money and I doubt it is a spark issue. Hard to beat the stock GM coil packs. If there was really an issue with the wires you see it in diagnostics or SES/CEL light with random or fixed misfires.

You can run an engine vacuum check to check for excessive exhaust back pressure but that may not be your issue either.

Are you running premium grade unleaded gas with that ZZP 1.0 PCM module installed?

[rickisrad]

I have not had it on the track yet. Yes I am running Shell 93 octane with 1/4 bottle of turbo 108 octane booster per tank. I agree with the MSD coil situation BNaylor, I was just reading up on the coil packs and decided that is not the way to go. I am going to fix the shotty job I did on the y bend. Do you think the 10.3 mm wires are affecting anything? I am also using the 606 iridiums, should I switch to something else? with the Mods I have I would expect to run well more that what I did. from stock I had 200 hp (175 if you take 25% loss at the wheels) I did not even run that on the dyno after all the mods, I was guessing I would get around 250 at the wheels at least. The car runs great and feels a lot stronger than before. Would the traction control affect anything on the dyno if he left it on?

[grandprixgtx00]

Originally Posted by rickisrad

I was guessing I would get around 250 at the wheels at least.

with the mods that you have, there is no way your gonna push 250 at the wheels, that would be like 285 at the crank...your lucky to get that outta a GTP with a 3.25" pully and supporting mods

[tblake]

Rick, might want to why your fuel ratio is slightly off. It should be at 14.7:1. Maybe its fine since your probably at full throttle. (I dont know) Maybe a Lazy O2 sensor?

[BNaylor]

It is probably OK Tim. On Dyno runs the pre CAT 02 sensor really is not used to control the fuel injection system. In most cases you are in open loop mode due to pedal to the metal and use of the 02 sensor is inhibited.

[tblake]

Gotcha!

[CrazyHorst]

There's kind of a sweet spot around 12.5-13.5 A/F ratios when going on a max power run....have to do several runs or a map to find out where this lies.

Relative to the mods posted, I see mostly exhaust work, there's still a catalyst in the pipe...while reducing exhaust backpressure is directionally correct, there isn't as much HP as you might think bottled up there (guessing 10bhp). The exhaust backpressure simulation for the actual production vehicle on a dyno is often set around 17" H20, whilst true dual pipes all the way back with 2 individual cats ala classic RWD V8 is around 10" H20.

FWIW, the main reason for reducing exhaust backpressure is to promote "cylinder emptying" and reduce "unintended EGR".

[rickisrad]

Originally Posted by grandprixgtx00

with the mods that you have, there is no way your gonna push 250 at the wheels, that would be like 285 at the crank...your lucky to get that outta a GTP with a 3.25" pully and supporting mods

I should be pushing more than 155 at the wheels, I would think? That seems kinda low. So is the WHP I ran normal?? what are some of your guys readings?

[grandprixgtx00]

Originally Posted by rickisrad

I should be pushing more than 155 at the wheels, I would think? That seems kinda low. So is the WHP I ran normal?? what are some of your guys readings?

yes, i would think you should be pushing somewhere around 200ish at the wheel. never got a stock GP dyno'd but the series III 3800 is rated at 205 or 210...cant remember to be exact, so the WHP would be somewhere around 180ish give er' take a little...

[BNaylor]

Originally Posted by grandprixgtx00

yes, i would think you should be pushing somewhere around 200ish at the wheel. never got a stock GP dyno'd but the series III 3800 is rated at 205 or 210...cant remember to be exact, so the WHP would be somewhere around 180ish give er' take a little...

You think?

Keep in mind this is a NA SIII 3800 engine which is rated at 200 engine hp @ 5200 rpm and 230 lb-ft torque @ 4000 rpm by GM which really doesn't mean anything. The only difference is the extra 5 lb-ft torque over the L36 SII 3800.

It is typical to get around 185 - 190 wheel hp in a stock L67 SII 3800. I've seen dyno tests on a stock L36 where if you got 145 whp on a Dyno that was considered good so his figures are really not that far off especially considering there are really no significant hp mods to his engine and it is a NA SIII 3800 engine. Based on the exhaust mods you might get 5 wheel hp if you are lucky.



For exhaust back pressure testing one of the easiest and inexpensive tests to run is an exhaust back pressure test with a regular automotive vacuum gauge 0-30 in-hg connected at an intake manifold vacuum source. After connecting the gauge start the engine at idle, slowly increase engine speed to 3,000 RPM, engine vacuum should be equal to or higher than idle vacuum at 3,000 RPM. If vacuum decreases at higher engine RPM's, excessive exhaust back pressure is present meaning some sort of corrective action should be taken.

Another test is to run a low pressure gauge (0-5 psi) at the exhaust system before the input of the CAT converter like at the 02 sensor port. The reading should not exceed 1.0 to 1.25 psi.

[grandprixgtx00]

i suppose...on a FWD car you lose alot of power going to the ground.

[BNaylor]

Originally Posted by grandprixgtx00

i suppose...on a FWD car you lose alot of power going to the ground.

Bingo!

Thats why I don't depend on Dyno tests or waste any money on them. Best place to test your car is at the track and get that timeslip.