Dynamometer Results & Comparisons - LS3 376/480 HO Dyno

Looking for thoughts on this. If chassis dyno used is spot on then max HP is within 25% drivtrain lost of GM's engine Dyno peak HP. 360 HP Vs 480 HP.

TQ on the other hand is 30% off peak engine dyno TQ. 329 TQ Vs 470.

What puzzles me is peak HP on GM's dyno sheet is at 5800 RPM. Peak HP on my sheet has moved out to 6506 RPM. I would have thought that peak HP like Peak TQ would still occur at same RPM as shown on Engine Dyno Sheet based on cam's design. Like everyone, I would have loved to see higher numbers. What I see is AFR is rich on low end, may be due to gear run was done in and/or exhaust. Any thoughts?

http://i258.photobucket.com/albums/hh276/jere-64/Filerev1.jpg

http://i258.photobucket.com/albums/hh276/jere-64/LS376-480-dyno-chart.jpg

Transmission is TCI 6X and rear gearing is 3.55. Run was done in 4th gear (3.55 X 1.18 = 4.19 drive ratio. Since car will trap in 4th gear in 1/4 mile, 4th may have been the better gear to tune in anyway) rather than 1:1 5th gear and converter was not locked. TQ converter is a Circle D dual clutch billet aluminum stalled in 2500 - 2800 range. If your wondering why such a low stall RPM, it's due to the 6X close ratio gearing which provides great RPM retention between shifts compared to 4l65 & 4L80 transmission gearing. Also because car will be autocrossed, not just straight lined raced.

TCI 6X (4L80E based)
2.93
2.23 -- 76.10% (high) RPM Retention -- 23.90% RPM DROP
1.57 -- 70.40% (high) RPM Retention -- 29.60% RPM DROP
1.18 -- 75.16% (high) RPM Retention -- 24.84% RPM DROP
1.00 -- 84.745% (high) RPM Retention -- 15.255% RPM DROP
0.75 -- 75.00% (high) RPM Retention -- 25.00% RPM DROP

4l65/70
3.06
1.62 -- 52.94% (high) RPM Retention 47.06% RPM DROP
1.00 -- 61.73% (high) RPM Retention 38.27% RPM DROP

4l80/85
2.48
1.48 -- 59.68% (high) RPM Retention 40.32% RPM DROP
1.00 -- 67.57% (high) RPM Retention 32.43% RPM DROP


Headers 1 3/4 tube, sort of a mid length, with not much of a collector because of need to get ground clearance, it had to be shorten to transition to 3.0" oval pipe at firewall. Muffler are Billy Boat Z06 NPP Fusion for 3.0" for wide open 3.0" exhaust from header back when needed.

http://i258.photobucket.com/albums/hh276/jere-64/PA250315.jpg

Air intake is home made cold air with dual 650 CFM filters feeding dual 3.0" piping stepped to 3 1/2' then to 4.0". MAF sensor used is LS2.

http://i258.photobucket.com/albums/hh276/jere-64/P7150532.jpg

thats probably right with those headers and unlocked, i would have guessed 390-400 in a well optimised stick car, but what doesn't make sense is the rpm difference between your dyno run and gm's advertised hp peak, you might run it on a different dyno or at the track, and tune wise i'd want it much closer to 12.8-13.0, that thing is soft down low!

I have tuned a couple of LS376 motors and they are very soft on the base tune. Leaning out the AFR will help a ton. It also looks like the power dropped off at around 4400-4600, that might be caused by false knock pulling out a bunch of timing. GM has to tune them conservative due to different intake and exhaust configurations.

You need some 1 7/8 headers move the maf out a bit and a different intake tube set-up. I picked up tq, hp and response goin from a 1 3/4 header to a 1 7/8 on my stock ls6.

You need 8-12inches of straight tube in front of the MAF for it to read properly.

With the help of another member with LS3 376/480 HO engine whose dyno sheet shows HP/TQ/AFR reading in 100 RPM increments, spotted why engine max HP peak didn't peak at about the same RPM as GM Engine Dyno sheet shows. Why it just looks like peak has moved.

His engine makes it Peak HP & TQ numbers about spot on with GM engine dyno 480 HO sheet. Looking at his AFR tells me why my engine looks like it making Peak power to/at 6500 RPM, it's not. It's that way because engine AFR is too Rich from 3000 RPM to 6000 RPM, then it leans out causing HP and TQ to increase above where HP should have peaked due to engine being to rich in peak HP RPM range. 6600 is about were HP would be as it falls off from cam's design real peak RPM...

The other LS3 376/480 engine's AFR is richer across the RPM range than my engine is. It's in the 9.0-11.0 range from 2500 to 6500 RPM. Mine is definitly too rich from 2500-6000, then from 6200-6600 AFR is probably close to being about right as GM's Engine Dyno Sheet reading is around 360-370 HP at 6500 RPM.

http://forums.corvetteforum.com/attachments/c1-and-c2-corvettes/47698165d1338944630-leaning-to-this-1st-graph-run11st-graph-run.jpg

http://forums.corvetteforum.com/attachments/c1-and-c2-corvettes/47698166d1338944630-leaning-to-this-1st-graph-11st-graph-.jpg

http://i258.photobucket.com/albums/hh276/jere-64/Filerev1.jpg


I have tuned a couple of LS376 motors and they are very soft on the base tune. Leaning out the AFR will help a ton. It also looks like the power dropped off at around 4400-4600, that might be caused by false knock pulling out a bunch of timing. GM has to tune them conservative due to different intake and exhaust configurations.

Like tws6 posted AFR needs looking at first, then depending on results and my desire to squeez out all the power out of the engine I can, air intake setup. Exhaust wise, I'm probably stuck with what I have. Would require custom fabed 1 7/8" headers and because of transmission size and lack of ground clearance, long tubes with merge collector can not be fitted. Had to modify 1 3/4" long tube headers that are on the car to fit.

Thanks to all, an especially to member who shared his dyno sheet with me. That helped both of us.

wow that things FAT! that can cause a Plethora of problems, i am surprised they continued the pull that out of tune!