I just dynoed my car this week and was wondering if anybody knew the drivetrain loss of an LT1 with a T-56 and a stock rearend??

 

I got the following results by comparing my engine dyno numbers (when the setup was still a T56) to the chassis dyno numbers:

Flywheel HP - % drivetrain loss

500HP - 12.6%
635HP - 12.3%
765HP - 12.1%

Thats with a Street Twin/steel flywheel, 3" chrome moly DS and Strange 12-bolt/3.73's

 

I've always thought it was around 10.5% since the LT1 is rated at 285 fwhp and dynoes around 255 rwhp.

255/285 = 0.895

1.0-0.895 = 0.105

0.105*100 = 10.5%

Dan

 

You're assuming:

1. The factory "rating" represents the actual flywheel HP - not necessarily so. And, allow for variations in HP among a large sample of cars.

2. All M6 285HP rated cars dyno at 255rwHP - they don't.

 

Wow, I would have though it to be slightly more than that!

Those are nice solid confirmed drivetrain loss numbers though. Not necessarily the same for everyone, but it gives a pretty good idea!

 

Thats because the lt1 is really rated at 300hp.

 

Maybe in the Corvette, but in the Firebird/Camaro, it was rated at 275 from 93-95 and 285 in 96-97 with the WS6/SS being rated at 305 in 96-97.

 

Another data point:

450HP - 13.0%

Stock clutch/flywheel/rear.

Dave

 

As you can see, and as makes for complete common sense, drivetrain loss is not a simple "%" - one-size-fits-all number. The drivetrain losses are made up of "fixed" components that do not change with engine HP (e.g. - inertia losses to rotating elements), and those that are roughly proportional to the power being transmitted (e.g. - gear and bearing friction losses).

For a stock engine, the % for an M6 may be closer to 13.5-14%. But I definitely wouldn't use the old rule of thumb "15% for manuals, 20% for automatics". The stock LT1 drivetrain is more efficient than that.

And, just to drop some more numbers, when I replaced the T56 with a TH400 and a loose, non-locking convertor:

500fwHP = 19.8%
635fwHP = 20.2%
765fwHP = 21.3%

That means 70 less rwHP at max flywheelHP.