motor to rwhp
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Melting Slicks
Joined: Jun 2002
Posts: 2,246
Likes: 66
From: Middletown CT
If you think about it, it really doesn't matter what the number is. What's important is what is getting to the ground. If you calculate your drivetrain loss at 18% rather than 12%, I guess it would give you bragging rights for an engine that's making more HP, but it wouldn't make your car any faster. Hey, I think I just found the cheapest mod yet. 15 HP for no money!
Melting Slicks
Joined: Mar 2001
Posts: 2,372
Likes: 51
From: New Milford CT
350 (Flywheel GM rated hp)-minus- (305rwhp average dyno on a stock LS1 vette) = 45 hp lost from the engine to rear wheels.
Contrary to popular belief, a fixed ratio like 12% or 18% doesn't really work, especially as the hp numbers get larger.
I think about 50 rwhp is a good rule of thumb for basic lost hp on most vettes, and then add another 5 rwhp lost for every 50 hp you add to the stock 350 flywheel hp.
Example 500rwhp Vette on the dyno, looses 50 + 5+5+5 = 65 total lost hp from engine to rear wheels. So the above Vette shows 435rwhp on the dyno.
These losses must increase the more and more as hp goes up because of rotational losses, and more friction in the driveline.
This is just my common sense view. By the way, if you go check out the Dynojet website, they tell you that you just can't reliably calculate flywheel hp starting from rwhp. I think we can however get a good approximation because of all the dyno data we have available on this forum.
Contrary to popular belief, a fixed ratio like 12% or 18% doesn't really work, especially as the hp numbers get larger.
I think about 50 rwhp is a good rule of thumb for basic lost hp on most vettes, and then add another 5 rwhp lost for every 50 hp you add to the stock 350 flywheel hp.
Example 500rwhp Vette on the dyno, looses 50 + 5+5+5 = 65 total lost hp from engine to rear wheels. So the above Vette shows 435rwhp on the dyno.
These losses must increase the more and more as hp goes up because of rotational losses, and more friction in the driveline.
This is just my common sense view. By the way, if you go check out the Dynojet website, they tell you that you just can't reliably calculate flywheel hp starting from rwhp. I think we can however get a good approximation because of all the dyno data we have available on this forum.
Team Owner
Joined: Jul 2003
Posts: 20,474
Likes: 2
From: Detroit
I think 15% is the general rule of thumb. Guessing crank hp is really just meaningless conjecture, IMHO. What counts is how much power you get to the rear tires and from there how much you can hook up ..
Cheers,
Mark
Cheers,
Mark