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Hello there,

If you want to know the hp at the wheels, do you have to multiply the flywheel hp with 0.8??

I ask this because I've read it somewhere in a magazine, but I think it is a lot of hp loss over the transmission etc.
If you have 500hp at the flywheel, do you get only 400hp at the wheels??? I would say something about 460-470.

Any comment would be great, thanks
David
 

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I would say 20% loss with the average car is close. I've seen as low as 13-15% on SOME late model manual trans cars but even then you're not sure as we're using the factory hp specs which are (in my opinion) SOMETIMES under-rated; I'm speaking of the LS1's here.

I was just speaking to a friend of mine yesterday about this exact topic. He's does exotic EFI conversions and chassis dyno's nearly all of them. He's done 6-8 where he tuned them on an engine dyno first, then installed them in the car and re-dynoed them on a Dynojet or DynoPak chassis dyno. He says every one he's done has lost closer to 25%.

The only way to know is to do both on your vehicle. I'm just finishing up a new engine for my 69 and considered doing both but decided just to do the chassis dyno. That tells me what's getting to the ground which is the most critical to me, plus around here it's about $600+ to get on an engine dyno.

Jody
 

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There was artical years back which studied accessory and drivetrain drag. A manual tranny was more effecient (sucked up less HP) than an auto by about 5-10%. I remember that stat but few others...but I recall A/C, power steering, smog pump, drum brakes all having some (varying degrees of) impact on rear wheel HP.

Anybody recall this artical?
 

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My 427 dyno'd at 428 horse and according to the Moroso power slide rule, it made 383 rear wheel hp once I went to the track. It had a automatic!
Peter
 

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Last summer we had a big car show at the local strip mall. They had a chassis dyno there and I had a blast watching guys get PO'd when there car pulled 80 or 100 HP less than the number they had been bragging about. I think the .80 rule is probably close with most automatic cars.
 

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And Charlie, that's right at 25% loss which is what Dan has found in several back-to-back tests.

This applies to the local Dynojet chassis dyno. Others can (and probably are) different.

Bottom line, EVERY car will be different. The ONLY way to know for sure is to do back-to-back test in and out of the car. Even then temp, humidity, etc. would need to be the same or compensated for to keep it equal. I've just heard people say that there's no way that you could lose 25% and I disagree.

Jody
 

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Edit (Sorry, I was way off with a reply after rereading the post).

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Robert

'69 getting better every day... (every pay day)

[This message has been edited by rojo (edited 11-20-2001).]
 
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