HP Loss in Drivetrain

1400 Views 5 Replies 5 Participants Last post by DaveZehak, Feb 23, 2001

CP

Discussion Starter · Feb 20, 2001

If the company advertises the engine as producing 385 horsepower and the dynos generally see 340 to 345 rwhp, then why don't we use that information to calculate the HP loss in the drivetrain to be right around 11%?

We seem to arbitrarily assign a 15% driveline loss, and then say the engine is already producing 400HP. If it's producing 385 horsepower with an 11% loss, you get the same rwhp. What would the incentive be for the General to underrate the engine? Are we deluding ourselves?

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TMiller

· #2 · Feb 20, 2001

I'm from East Texas, so I don't get out much, but I never have figured out the magazines saying that the (American)factories don't know how much power their engines produce.

Seems to me if the LS6 made 400hp, they would be telling anyone who would listen. They sure didn't hesitate to say the ZR1 made 400hp...

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SWCDuke

· #3 · Feb 22, 2001

Nobody knows for sure what the actual drivetrain drag torque/power curve looks like. You are correct - the drivetrain loss may be less than 15 percent which means the engine is accurately rated. The "15 percent" bandied about is just an estimate based on an intuitive average for a wide range of cars.

Until someone actually conducts a scientific test of drivetrain drag torque/power everyone is just guessing.

On the other hand GM may be getting nervous over increasing power ratings, and in order to keep the Corvette insurance friendly and out of the focus of the various government and private safety nazi organizations, they may have decided to rate the engine very conservatively.

Duke

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Dennis Jurs

· #4 · Feb 22, 2001

Interesting thread. I noticed a thread today on the Viper Forum asking the same question realative to the Viper. The only way to accurately know is to dyno an engine outside of the car, then install it, and dyno it on a chassis dyno and compare the #s.
Seems a Viper race team did just that, and got a 12.7% difference between the two.
I would suspect the Corvette drivetrain to have a slightly larger parasitic loss due to
it's design, so the 15% figure we see, may be pretty close.
I recall the ZR1s were initally rated at 375HP or there about when the LT5 first came out, and were then rated to 405HP later. Overall performance figures however, really didn't change much (the ZR1 guys would know more about this).
I would guess that the LS6s are putting out at least as advertised, more likely a tad more.

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SWCDuke

· #5 · Feb 23, 2001

<BLOCKQUOTE>quote:</font><HR>Originally posted by DaveZehak:
Dennis I always thought it was kind of fishy that the 405 hp ZR1 ran no better than the 375hp version.
<HR></BLOCKQUOTE>

Supposedly the only difference when the power rating went to 405 was some hand port blending of the heads. Production got so low that they had plenty of extra time to do some hand work. Such work would probably only show a noticable torque/power difference about 4000 revs.

Duke

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DaveZehak

· #6 · Feb 23, 2001

Dennis I always thought it was kind of fishy that the 405 hp ZR1 ran no better than the 375hp version.

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Dave Zehak
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