C3 Drivetrain Loss

[enkeivette]

Some of you, namely Ben, will find this interesting. Motorhead on CF did an engine dyno with a 406, then immediately dropped it in his 81 and did a chassis dyno. He calculated a 23% drivetrain loss! With a modern manual trans.

So revise your calculations Ben.

[SeanPlunk]

Some of you, namely Ben, will find this interesting. Motorhead on CF did an engine dyno with a 406, then immediately dropped it in his 81 and did a chassis dyno. He calculated a 23% drivetrain loss! With a modern manual trans.

So revise your calculations Ben.

What kind of dyno? A 23% loss is A LOT for a manual car...

[Vettezuki]

Some of you, namely Ben, will find this interesting. Motorhead on CF did an engine dyno with a 406, then immediately dropped it in his 81 and did a chassis dyno. He calculated a 23% drivetrain loss! With a modern manual trans.

So revise your calculations Ben.

Same facility, operating temps, atmospheric conditions? A lot of params in there, to say nothing of differences in chassis dynos. It wouldn't surprise me if it's higher than a modern Vette, but 23% is massive. That would mean my engine is 480BHP.

[enkeivette]

Same facility, operating temps, atmospheric conditions? A lot of params in there, to say nothing of differences in chassis dynos. It wouldn't surprise me if it's higher than a modern Vette, but 23% is massive. That would mean my engine is 480BHP.

I argued with him about it first too, but he is including the full exhaust and the accessories in the 23%.

So it's not just 23% drivetrain loss, but including everything it's a 23% loss from gross power as he calls it. He's a smart guy, taught me a lot of what I know about tuning carbs. If it were anyone else I probably wouldn't buy it.

I can only image how much the autos are losing.

[enkeivette]

http://forums.corvetteforum.com/c3-tech-performance/2583633-427ci-small-block-says-hello-to-7000rpm-on-the-chassis-dyno.html

[enkeivette]

What kind of dyno? A 23% loss is A LOT for a manual car...

Don't know what kind of dyno.

[enkeivette]

I was really shocked to see this too. When the guys at DC dyno day were talking about a 25% drivetrain loss for their C3s I was definitely rolling my eyes. I guessed the usual 15% for manuals, maybe another 2 or 3% for the IRS.

[Vettezuki]

I argued with him about it first too, but he is including the full exhaust and the accessories in the 23%.

So it's not just 23% drivetrain loss, but including everything it's a 23% loss from gross power as he calls it. He's a smart guy, taught me a lot of what I know about tuning carbs. If it were anyone else I probably wouldn't buy it.

I can only image how much the autos are losing.

You mean like accessories under load? (A/C on)? That'd change it a little but not a lot. Also, if he went from open headers on the engine dyno to stock exhaust on the chassis, or even just inserting an old fashioned cat, that's a potential killer. Still count me in the skeptical here.

[enkeivette]

Yeah, straight headers to full exhaust, not even a loud exhaust. I doubt the AC was on, don't even know if he has a compressor.

[enkeivette]

Wheel horsepower is all that really matters anyways. Who cares what your motor can do on a bench. My Neon is faster than a Miata because I have less loss, it is what it is. I just thought it was interesting.

[94cobra69ss396]

Popular Hot Rodding did the same thing with their project Chevelle and saw a 28% loss at the wheels. Their 496 made 626hp at the flywheel but only put down 448 at the wheels through a TH400. It made me feel good when they only made 448rwhp because my Chevelle put down 461rwhp with the 454 and my cars drivetrain is set up almost identical to theirs. When I built the engine I figured it would make about 620hp so it looks like I made a little more. Plus their best time so far has been 11.30 at 117 and mine on the engine has been 11.07 at 121.

[Vettezuki]

Popular Hot Rodding did the same thing with their project Chevelle and saw a 28% loss at the wheels. Their 496 made 626hp at the flywheel but only put down 448 at the wheels through a TH400. It made me feel good when they only made 448rwhp because my Chevelle put down 461rwhp with the 454 and my cars drivetrain is set up almost identical to theirs. When I built the engine I figured it would make about 620hp so it looks like I made a little more. Plus their best time so far has been 11.30 at 117 and mine on the engine has been 11.07 at 121.

That's AT though right? That would certainly be a bit higher.

[94cobra69ss396]

That's AT though right? That would certainly be a bit higher.

Yes. The TH400 is the turbo 400. It's stronger than the TH350 but also takes more hp to turn.

[jedhead]

Unless my STS-V is a factory freak or the dyno is reading high, I only had a 17.5% driveline loss based on rated 469hp with 387whp on the dyno. I had an 18% loss on my Taurus SHO with a manual.

Bob

[94cobra69ss396]

Unless my STS-V is a factory freak or the dyno is reading high, I only had a 17.5% driveline loss based on rated 469hp with 387whp on the dyno. I had an 18% loss on my Taurus SHO with a manual.

Bob

Yes but you have to remember that those flywheel numbers are SAE net numbers. That means the engine was tested with all belt-driven accessories, air cleaner, emission controls and a complete exhaust. Whereas the 496 for example was tested with open headers and an electric water pump only.

[Vettezuki]

Unless my STS-V is a factory freak or the dyno is reading high, I only had a 17.5% driveline loss based on rated 469hp with 387whp on the dyno. I had an 18% loss on my Taurus SHO with a manual.

Bob


This is more of what I typically expect. I wonder if the older cars have more loss through the old diffs and heavy axle/half shafts + u-joints. :huh:

[94cobra69ss396]

Possibly. I know that there is no way the Cobra is making 600+ at the flywheel which is what it would be with a 25% loss. I figure it to be closer to 520-540 which would be about 15% on the race gas tune.

[enkeivette]

Popular Hot Rodding did the same thing with their project Chevelle and saw a 28% loss at the wheels. Their 496 made 626hp at the flywheel but only put down 448 at the wheels through a TH400. It made me feel good when they only made 448rwhp because my Chevelle put down 461rwhp with the 454 and my cars drivetrain is set up almost identical to theirs. When I built the engine I figured it would make about 620hp so it looks like I made a little more. Plus their best time so far has been 11.30 at 117 and mine on the engine has been 11.07 at 121.

That's pretty crazy, I wouldn't expect anymore than 20% with an auto through a solid axle. I can only imagine how much the Vettes eat up through a auto with the IRS. It must be in the 30% range.

[enkeivette]

But Ron brings up a good point. We are counting total loss of hp, not just drivetrain loss. If the motor was tested on the engine dyno with accessories and a full exhaust it wouldn't have lost that much just through just the drivetrain.

[Vettezuki]

But Ron brings up a good point. We are counting total loss of hp, not just drivetrain loss. If the motor was tested on the engine dyno with accessories and a full exhaust it wouldn't have lost that much just through just the drivetrain.

Oh I misunderstood his test. I thought he had the engine fully dressed on the engine dyno and was measuring a 23% loss through the driveline alone basically. Let's say a more expected driveline loss is around 17% +- 1~%. That means there's something like an additional 5% from the accessories and exhaust. That's totally believable.

[enkeivette]

Oh I misunderstood his test. I thought he had the engine fully dressed on the engine dyno and was measuring a 23% loss through the driveline alone basically. Let's say a more expected driveline loss is around 17% +- 1~%. That means there's something like an additional 5% from the accessories and exhaust. That's totally believable.

Yeah, you did the same thing I did. My first response to him was, 23%? Don't believe it.

[BADDASSC6]

Well This does seem accurate, but it's all int he definition of drivetrain losses. Most people call drivetrain losses as power that the motor is actually making that is lost in the inefficiency of the rest of the drive train. Here we are talking about a motor that was dynoed on two different dynos with different exhaust and other minor differences. If I dyno my car with open long tube headers then drop it in a car with stock manifolds. The chassis dyno will also show a +20% loss. Even greater with true 180 degree headers.

[jedhead]

Yes but you have to remember that those flywheel numbers are SAE net numbers. That means the engine was tested with all belt-driven accessories, air cleaner, emission controls and a complete exhaust. Whereas the 496 for example was tested with open headers and an electric water pump only.

So the 496 flywheel horsepower numbers is more inline with the gross hp numbers of old then? That would explain the larger hp loss to the wheels.
BTW, the AC was running on my dyno run, I forgot to turn off the climate control or shut off the AC. I found out that in the STS-V the AC compressor is still engaged at WOT unlike most cars that I am used to that shuts off the compressor at WOT.

Bob

[94cobra69ss396]

So the 496 flywheel horsepower numbers is more inline with the gross hp numbers of old then? That would explain the larger hp loss to the wheels.
BTW, the AC was running on my dyno run, I forgot to turn off the climate control or shut off the AC. I found out that in the STS-V the AC compressor is still engaged at WOT unlike most cars that I am used to that shuts off the compressor at WOT.

Bob

Exactly, it is just like the old SAE gross numbers.

I'm surprised that your compressor didn't shut off at WOT. I thought that they did this to one help power output but two to help with fuel mileage.

[jedhead]

I was suprised too that the compressor doesn't shut off at WOT. Who knows, I might have been able to squeeze out a couple more hp with the compressor off. Next time, I'll remember.

Bob