BraemerZ28

iTrader: (2)

Subject in question... 2008 Sierra Denali with simple mods - cold air intake, 1 7/8 American Racing long tubes, Corsa cat back, and a dyno tune. Before and after curves on the dyno are pretty much exact same shape, just moved up thanks to the usual fuel and spark adjustments. Pretty much what I expected since I kept the stock cam.

My question is, what may be the reason for the flat line hp number from 5400 to 5900? Same thing was there before tuning.

I'm assuming that it simply points to the characteristics of the stock cam? But then I got thinking about it and was wondering if it might be indicativve of a stock valve spring limitation (float)? I also thought about an intake or head bottleneck, but since the power is staying the same but still allowing RPM top grow, I didn't think it was a lack of air? Injector duty cycles are 90% at 6000 rpm so it's not running out of fuel.

Truck runs great - HPT log shows 0-60 in 6.1 seconds which is about 1.1 better than stock. MPG on 130 mile mixed round trip with air on was 18.5. Not bad for a lifted, 6000 lb, all wheel drive truck running 33x12.5R20's that weigh 97 lbs each.

Just wondering what may be the next opportunity I might chase down, and this flat spot drew my attention.

Thanks for any thoughts.

Chris10an

iTrader: (1)

Hello Sir. Here's a dyno of a 5,3L. Mods are: Headers, Stock Ls1 Intake with stock Injectors. 85MM Throttle body. Roller Rockers. 1-7. no gain there.
Tuned with EfiLive.
What is the exact hp and torq of that engine? It's a 6,2 right?
Is your AFR down to 16 -17 @ VOT? Looks a little lean/reach in the start?

My engine run in a 72 Blazer K5 4x4 with a 4L60E and a NP 205
It's lifted and runs almost the same tires.

BraemerZ28

iTrader: (2)

Sounds like a cool truck. I always liked the old K5's, especially the fact that you could take the rear part of the roof off.

Yes, it's a 6.2 liter. Stock advertised power is 405 hp and 417 lb-ft. I don't have a stock curve at the wheels for my truck because I put the mods on before I went to the dyno. The before tuning curve looks exactly like the one posted above, just moved down about 15 hp and 20 lb-ft.

It might be hard to read on the small chart I posted, but the AFR settles right in around 12.6 - 12.8 above 3000. Stock tune was running about 11.5 in PE mode . Anything on the chart below 3000 can really be ignored as the dyno operator wasn't at full throttle yet and the truck wasn't calling for PE mode which is why it is floating around 14.7.

Your curve looks like I expected mine to - a build up to a peak and then a gradual fall off. But mine has that flat top on it which leads me to think that there is something unrelated to airflow that is limiting me...

Any ideas?

Thanks!

rsz288

Running VVT?

Chris10an

iTrader: (1)

I'm not a specialist, only sharing what I'm thinking.
Plugs are OK? New or stock? Air filter is big enough?
Fuel pump problems? What is the pressure @ VAT 5000rpm and up?
Fuel type? Someone else tuned this ECU before?

BraemerZ28

iTrader: (2)

Yes, running stock VVT. He tried to tune it - take some out sooner, add some in later, etc but it seemed that GM had it optimized so it's running stock VVT settings.

Truck only has 16000 miles on it so plug should be good. Air filter is brand new K&N with Air-Aid intake tube from TB to stock airbox. Fuel pump should be good - injector duty cycles touch 90% at 6000 rpm but doesn't seem like it's overloaded. Fuel pressure is 58 psi. 91 octane.

ECU is stock. I had messed around with trans settings before he got it, but that's it.

Thanks.