Massive RWHP Loss On Dyno

[Gremlin85]

Hey guys, this might be a long read but I could REALLY use some input, advice and help....




I've spent the last couple days picking my brain and the brain's of others to come up with an answer to a growing concern I have about my most recent dyno results.

If you know my thread about putting Long Tubes on the Coyote motor without a tune, then you know I've been compaing dyno results for a while now. Here is my thread:

http://www.s197forum.com/forum/showthread.php?t=111564

The last numbers I put down were 383 RWHP (SAE Corrected) with just Long Tubes, Catless Mids (X-pipe) and RTR Axel Backs.

Well, since then I've added a Airaid CAI, Boss 302 Intake Manifold and I've gone through several tunes. I've learned about this motor a bit and re-tuned my car using HP Tuners. Car felt pretty decent (except for low end tq loss from Boss IM) and I've had a consistant 4.6-4.8 60-100 Using my tune.

I just went to the dyno (same one I used every other time) to see the fruits of my labor and get a sense of my progress in power....

Well, after 3 pulls I put down 386RWHP. Needless to say I was shocked and extremely sad with a hint of being pissed. Just to be sure, I loaded every tune I purchased and did pulls with each one to compare.... all were lower than my custom tune by about 3-7 RWHP! So the tune was not at fault. AND just to be 100% sure, I loaded the stock tune (I know it's not a good idea with my mods, but I just had to narrow the problem dow) and I did a quick pull.... 351RWHP! When I was bone stock I put down 368RWHP SAE Corrected.

Now, I've been told that it was because of the heat and 70% humidity on Friday here in Massachusetts. It was about 94 degrees in the shop when the pulls were done. It was about 55 degrees and raining on my stock pull and about 65-70 degrees out and way less humidity on my LT's and no tune pull.

So could that much heat cause THAT much of a power loss, or is my car having a serious issue that I need to track down?????

There is no CEL, no running issues, no idle issues, no AFR issues, fuel trims are good but my left bank is a couple % richer than my right bank according to my logs STFT and LTFT readings.

Others and myself are completely stumped. The guy running the dyno said he has never seen an NA car have such a power loss from a previous pull and only see's that on high powered boosted cars - which makes total sense. I have not found anyone who has had similar results like mine with no hint of an issue with the car. It runs great, at least to me. I have nothing to compare to.


So, any ideas on why I've gain nothing from all those mods AND a tune??? Anything else you need to know to help?




Short version: A no tune dyno run was 383RWHP with long tubes, catless mids and rtr axel backs. Added Boss IM, CAI and tuned and only put down 386RWHP. Same dyno.

 

[stkjock]

the corrected numbers should take the weather into account.

not likely - but are you certain the pulls were all done in the same gear?

 

[Gremlin85]

the corrected numbers should take the weather into account.

not likely - but are you certain the pulls were all done in the same gear?

Absolutely. I wanted to make sure everything was the same as before when I was stock so all pulls since the start of all this were done in 4th gear.

All numbers mentioned were corrected numbers. I know they are supposed to compensate for weather so I got 3 WHP for all my mods and a tune. All tunes showed the same results. I even asked if the dyno was calibrated recently and it wasn't.

 

[stkjock]

why 4th? you have a MT82 based off the sig I viewed, 1:1 is 5th in the transmission


if you really want a good alternate comparison - take it to the track and just look to MPH it to see where it traps

 

[slagburn]

Take it to the track instead of fretting about dyno numbers.

 

[Gremlin85]

why 4th? you have a MT82 based off the sig I viewed, 1:1 is 5th in the transmission


if you really want a good alternate comparison - take it to the track and just look to MPH it to see where it traps

I did 4th when it was stock as to not hit the speed limiter. To keep it consistant, I continued to dyno in 4th.

Take it to the track instead of fretting about dyno numbers.

As far as track stuff, I've never been with this car so I'll have nothing to compare it with.

 

[JeremyH]

Yes normal, regardless of sae corrections dyno on a cold day with low humidity will always be more fruitful than a really hot day with high humidity. Just like et at the track.

 

[Gremlin85]

Yes normal, regardless of sae corrections dyno on a cold day with low humidity will always be more fruitful than a really hot day with high humidity. Just like et at the track.

So in that sense, the SAE corrections will vary as well? All numbers listed are with SAE Corrections. So my no tune pull was 383 and my tune with more mods was only 386. All SAE Corrected.

I'm sorry, I just thought the SAE corrected numbers were to be more useable in comparing from day to day and weather conditions. I thought that's why they are corrected numbers?

I'm confused lol.

 

[JeremyH]

Yes from my experience. Ive seen numbers be lower on sae or higher on sae under like conditions. If you want to see what your car is really making that day use std or uncorrected. The big factor here is da or density altitude which the dyno isn't accounting for as far as I know. I have seen 30rwhp lower on a high da day just like a car will run slower at the track with da is high doesn't matter what correction you use on a dyno.

 

[Gremlin85]

Uncorrected was in the 36x's. I felt sick to my stomach lol.

 

[Gremlin85]

So these motors are that sensitive to heat?

My 2004 Pontiac GTO was always within a couple horsepower no matter what day I dyno'd on if I used the SAE corrected numbers.

 

[johnnyv8]

Can you load up a picture of both dyno graphs (the exhaust vs all your new bolt ons)?

 

[JeremyH]

Uncorrected was in the 36x's. I felt sick to my stomach lol.

Makes sense it will make less power on a hot day and sae is assuming 70 degrees so the sae numbers are higher.

In other words don't sweat it as long as the car is running good and trapping what it should.

 

[Gremlin85]

Can you load up a picture of both dyno graphs (the exhaust vs all your new bolt ons)?

I left without them. I'll email the shop for a copy.

 

[JeremyH]

So these motors are that sensitive to heat?

My 2004 Pontiac GTO was always within a couple horsepower no matter what day I dyno'd on if I used the SAE corrected numbers.

Yes, pcm controlled dual widebands, knock sensors and iat. The computer likes to add fuel when the temps are higher which will richen the tune and make less power to keep the engine safe.

 

[fdjizm]

What does the dyno sheet trap tho?

 

[Gremlin85]

Yes, pcm controlled dual widebands, knock sensors and iat. The computer likes to add fuel when the temps are higher which will richen the tune and make less power to keep the engine safe.

I have no KR and am gettign commanded timing. Verified this on the dyno. I also disabled cat over-temp because I've removed them and it gives the commanded Lambda/AFR. I run an 11.9 AFR at WOT throughout the rev range.

What does the dyno sheet trap tho?

I'm just looking for improvements over the last dyno to get before and after results. Just a little testing I've been doing to get the most out of my mods. I am in no way aiming for a specific number or using these for anything other than seeing gains or losses from prior dyno sessions.

 

[JeremyH]

Why are you running such rich a/f? I run 11.8-11.9 afr with 16-18lbs of boost.

N/A a/f should be in 12.9-13.5 range.


Like I said don't waste your time trying to compare pulls on a 94 degree day with 70% humidity to pulls on 55,65,70 degree days. If da is high or low there is less/more oxygen in the air and power can very regardless of dyno correction factors. Look up what the da is in your area at the shop and that will tell you what you need to know.

 

[Gremlin85]

Why are you running such rich a/f? I run 11.8-11.9 afr with 16-18lbs of boost.

N/A a/f should be in 12.9-13.5 range.


Like I said don't waste your time trying to compare pulls on a 94 degree day with 70% humidity to pulls on 55,65,70 degree days. If da is high or low there is less/more oxygen in the air and power can very regardless of dyno correction factors. Look up what the da is in your area at the shop and that will tell you what you need to know.

It's been told that the Coyote motors run richer.

I'll be going back in October to compare.

 

[JeremyH]

12.9-13's is richer, I ran 13.8-13.9 afr with my 9.8:1 compression 3v na. So high 12s is decently rich for a na coyote, let alone high 11's.