help me understand HP!

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Sep 14, 2006 | 05:20 PM

vette4db

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Racer

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help me understand HP!

I read a lot of post regarding rwhp and rwtq numbers. I am learning as I go and I am just trying to understand how it works. My question is if GM says the C6 puts out 400 hp then what does that equate to at the rearwheels? If someone dynos at say 355 rwhp then that is more than 400 hp right? Just curious how it all works.

Sep 14, 2006 | 05:24 PM

RushThruLife

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From: GEAUX TIGERS PSL FL.

Engines are tested at the flywheel with no drivetrain drag. Theres about a 12 to 15% loss of HP through the drivetrain. Thats where the lower numbers come into play. 400hp x 85% = 340hp.

Last edited by RushThruLife; Sep 14, 2006 at 05:27 PM.

Sep 14, 2006 | 05:29 PM

Landru

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Joined: Dec 2002

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From: Wayne Township WI

Quote:

Originally Posted by vette4db

An engine's HP's tested without a transmission, drive shaft and all other things that'll reduce the final rear wheel horsepeower number from what's stated.
I believe that's the difference between BHP (Brake HP) & RWHP; although, if I'm in error I'm sure it won't be long before it's pointed out.

And no 355HP < 400HP.

Sep 14, 2006 | 05:33 PM

Zig

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From: stafford country, va. Avatar: Me on turn 3 @ Bristol (The World's Fastest Half-Mile)

Quote:

Originally Posted by vette4db

I read a lot of post regarding rwhp and rwtq numbers. I am learning as I go and I am just trying to understand how it works.

My question is if GM says the C6 puts out 400 hp

the 400/400 trq/hp numbers are at the crank, using an engine dyno, not a chassis dyno. most of the 'power' numbers you see talked about on the 'boards' will be from a chassis dyno.

Quote:

then what does that equate to at the rearwheels?

depends upon the efficiency of the driveline. vehicles loose a certian amount of power from 'driveline or parasitic loss'. not too much one can do about it. it will average from 10 to 15 percent loss, depends upon the vehicle.

Quote:

If someone dynos at say 355 rwhp then that is more than 400 hp right? Just curious how it all works.

different dynos will report different numbers for the same vehicle.

however, 355 (rwhp/trq ) plus 12.6 (driveline loss) percent is 399.73 crankshaft hp/trq.

Last edited by Zig; Sep 14, 2006 at 05:36 PM.

Sep 14, 2006 | 05:52 PM

jjohn918

Drifting

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From: Fountain Inn SC

Here is another interesting tid bit too. Currently I believe that GM is the only company that certifies HP.

Sep 14, 2006 | 06:09 PM

vette4db

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Racer

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So how can GM state that the C6 puts out 400hp when in actuality, it can be more or less depending on the vehicle. How can they say that every engine puts out 400 hp?

Sep 14, 2006 | 06:22 PM

talon90

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Quote:

Originally Posted by vette4db

So how can GM state that the C6 puts out 400hp when in actuality, it can be more or less depending on the vehicle. How can they say that every engine puts out 400 hp?

The test engine is built and tested. Once it is tested and blueprinted, the rest of the engines are assembled from that blue print. They now have documented proof that that engine, built to those specifications can produce 400 bhp. Every engine will have a tolerance. In the C5's stock six speeds were found to produce anywhere from 293 to 305 as I recall. Maybe plus or minus a pony or two at the wheels from a 350 bhp LS1. Stock for stock the drive line loss was believed to be 15% for the six speed while the automatic was believed to be 18% as I recall.

Horse Power on Wikipedia:

http://en.wikipedia.org/wiki/Horse_power

Horse Power on "How Stuff Works":

http://auto.howstuffworks.com/horsepower.htm

Last edited by talon90; Sep 14, 2006 at 06:26 PM.

Sep 14, 2006 | 06:24 PM

Wayne O

CF Senior Member

Joined: Feb 2006

Posts: 23,313

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From: Tucson Arizona

Quote:

Originally Posted by RushThruLife

Engines are tested at the flywheel with no drivetrain drag. Theres about a 12 to 15% loss of HP through the drivetrain. Thats where the lower numbers come into play. 400hp x 85% = 340hp.

RushThruLife....am I seeing tire tracks on that dog in your Avatar??