8.1 power gains

[Hog]

Guys with access to chassis dyno's, or anyone with 8.1 experience.

What kind of power gains are you seeing with PCM tuning alone?

Do you see much of a difference between tuning an 8.1 in a 3/4-1 ton application or an 8.1 in a Medium duty commercial truck application like a motorhome?


I read somewhere that 50+rwhp gains could be had tuning the 8.1 PCM.
Drop in a cam and tune the PCM, I would think that 100hp at the crankshaft gain could had.

Whats the factory rev limit of a 8.1 3/4-1ton truck application?


thanks

peace
Hog

[Hog]

I just found some 8.1 dyno PCM tune numbers.


Stock tune on 92 - 247.52 HP 336.25 Torque
Tuned w/ EFI Live on 92 - 272.17 HP 374.91 Torque
Tuned w/ EFI Live on E85 - 304.79 HP 402.58 Torque

01 Chevy 2500 HD ECLB 4x4 w/ 8.1 pulled on a Dynojet dyno w/right headlight removed, Truck is stock minus tune and 225k on motor. Allison Tranny


peace
Hog

[n0dih]

I think Lyndon was working with a guy in Colorado on a 8100 Suburban and was getting 380+ wheel hp on it. No engine mods IIRC. There was a lot from the customer on one of the Avalanche forums.

Originally Posted by Hog

I just found some 8.1 dyno PCM tune numbers.


Stock tune on 92 - 247.52 HP 336.25 Torque
Tuned w/ EFI Live on 92 - 272.17 HP 374.91 Torque
Tuned w/ EFI Live on E85 - 304.79 HP 402.58 Torque

01 Chevy 2500 HD ECLB 4x4 w/ 8.1 pulled on a Dynojet dyno w/right headlight removed, Truck is stock minus tune and 225k on motor. Allison Tranny


peace
Hog

[Hog]

380rwhp? If thats true thats great. 380 crank converts down to just over 300rwhp. Coincidence?

I would like an 8.1 in a rcsb.

peace
Hog

[n0dih]

I think at some point 400 whp was attained. Need to confirm. And maybe Lyndon can comment, this one he probably remembers, there was a lot of back and forth on this one.

Originally Posted by Hog

380rwhp? If thats true thats great. 380 crank converts down to just over 300rwhp. Coincidence?

I would like an 8.1 in a rcsb.

peace
Hog

[Programmer]

Originally Posted by Hog

380rwhp? If thats true thats great. 380 crank converts down to just over 300rwhp. Coincidence?

I would like an 8.1 in a rcsb.

peace
Hog

It never converts...
For example...someone has a stock Suburban that makes 300 rear wheel hp. Someone thinks that 20% losses substantiates 360 at the flywheel.
Person puts a supercharger on his sub, and now he's making 410 at the rear wheels. Same math says that should substantiate 492 hp at the flywheel.
Why did the driveline losses go up with nothing but a supercharger install ?
(60 hp driveline losses stock...82 hp driveline losses with supercharger)
Percentages don't work to backcalculate to the crank...

[Hog]

Originally Posted by Programmer

It never converts...
For example...someone has a stock Suburban that makes 300 rear wheel hp. Someone thinks that 20% losses substantiates 360 at the flywheel.
Person puts a supercharger on his sub, and now he's making 410 at the rear wheels. Same math says that should substantiate 492 hp at the flywheel.
Why did the driveline losses go up with nothing but a supercharger install ?
(60 hp driveline losses stock...82 hp driveline losses with supercharger)
Percentages don't work to backcalculate to the crank...

I do see where you are coming from.

Did the driveline losses go up due to increased friction on all bushings, bearings, gears, in the driveline increased torque converter slippage? I would think that the more force you apply on mechanical links, the greater the friction these links may exert, this increasing driveline losses?

I dont know, I'm just discussing. I would think the only surefireway to measure driveline losses would be to dyno the engine using and engine dyno with the same intake and exhaust, then install said engine into the vehicle and then dyno away. A problem with this would be the differences between the engine and chassis dyno.

Do you care to comment on the 400rwhp 8.1 that had no engine mods on it??

peace
Hog

[Programmer]

I've seen people decel off the top of a dyno run, and explain -- "that's the frictional loss in the drivetrain." Actually, decel friction changes with decel RPM, so--again it's possibly a constant that should be recorded by the dyno, and integrated to the result graph.
Load friction--that will always rise with HP...and it's not a percentage. I really don't even know at this time how to calculate it accurately back to a "crankshaft"...it'd be complicated math, and require a lot of input data at the dyno terminal.

One of our race guys had his 1100 HP Alcohol car on our dyno, and after making 780HP said our dyno was whacked. I told him, he doesn't undestand driveline losses...and why would he think that 1100hp at the crankshaft would EVER be the same at the wheels with a 5500 stall, 5.13's and jello tires. The tires alone could be absorbing 20% !

As for the 400rwhp 8.1l, I'm unsure of the client and it wasn't tested on our dyno as far as I can recall.

[Hog]

"Jello tires" that's a great way to describe them, and no doubt would contribute to huge drivetrain losses.

Thanks for the input.

peace
Hog