True HorsePower
Drifting
Joined: Oct 2006
Posts: 1,947
Likes: 8
From: Redwood City CA
Don't most people just assume a 15% drivetrain loss and multiply the rwhp by 1.15? That sounds about right...The C6 Z06 dynos at 439ish stock.... 439 * 1.15 = 504.85
Mine
: 429rwhp * 1.15 = 493 bhp
Ignore my post above...Apparently, I was wrong.
Mine
: 429rwhp * 1.15 = 493 bhpIgnore my post above...Apparently, I was wrong.
Last edited by jpandes; Aug 18, 2008 at 06:54 PM.
Burning Brakes
Joined: Apr 2007
Posts: 1,030
Likes: 1
From: Douglasville Ga
Although 15% loss has been discussed at length and you might get a WHOLE lot of different answers on this, 15% is a good estimate, but the really important thing is how much gets to the road and how well you know how to us it.
Melting Slicks
Joined: Feb 2001
Posts: 2,800
Likes: 356
From: Northville, MI
Chassis dyno's are mostly used for comparison tuning. Dyno the car, make the changes, re-dyno the car and measure the difference to SAE standards. Comparing the amount of drive train/rotating mass loss from one day to another on a chassis dyno can be very misleading. You know every C6Z leaves the factory at 505 hp SAE and if you were to make three dyno pulls and you will see the different hp readings and they more that likely are different from someone else's hp claims. Then you have the different types of dyno's--drum, load bearing, etc....otherwise know as dynojet, mustang, etc.
Bottom line there are some general "rule of thumbs" but non are accurate
Bottom line there are some general "rule of thumbs" but non are accurate
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
OP -- read this thread. This question has been beat over and over and over again.
http://forums.corvetteforum.com/show....php?t=2083989
Last edited by ZeeOSix; Aug 18, 2008 at 03:44 PM.
Tech Contributor
Joined: Apr 2007
Posts: 10,924
Likes: 78
From: Forney Texas
Not quite. The formula for RWHP from BHP (Crank) is BHP*0.85 = RWHP. So to go backwards it is RWHP/0.85 = BHP.
Although 15% loss has been discussed at length and you might get a WHOLE lot of different answers on this, 15% is a good estimate, but the really important thing is how much gets to the road and how well you know how to us it.
Although 15% loss has been discussed at length and you might get a WHOLE lot of different answers on this, 15% is a good estimate, but the really important thing is how much gets to the road and how well you know how to us it.
Multiplying by 1.15 and dividing by .85 provides you with 2 different answers. Dividing by .85 is the correct way.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Racer
Joined: Nov 2007
Posts: 327
Likes: 0
Exactly
Drifting
Joined: Oct 2006
Posts: 1,947
Likes: 8
From: Redwood City CA
Ok, my bad. But wait...If I convert rwhp to bhp by dividing 429 rwhp by .85 I get 504 bhp. WOo-hOo!
Last edited by jpandes; Aug 18, 2008 at 06:56 PM.
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
The general rule of thumb is a 15% drivetrain loss for a manual transmission and 20% for am automatic. However, people still use those percentages no matter what the car is putting down at the wheels. That doesn't make a whole lot of sense to me, as I do not believe drivetrain losses will increase in a linear manner with power output. About the only real measure, IMHO, would be to pull the engine and dyno it, and then reinstall it and dyno the car at the wheels. Obviously, no one would want to do that, which, come to think of it, is probably why 15% and 20% are always used. 
Ed
Ed
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
The general rule of thumb is a 15% drivetrain loss for a manual transmission and 20% for am automatic. However, people still use those percentages no matter what the car is putting down at the wheels. That doesn't make a whole lot of sense to me, as I do not believe drivetrain losses will increase in a linear manner with power output.
Pro
Joined: Aug 2005
Posts: 571
Likes: 1
From: Virginia Beach VA...originally Burtonsville, MD
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
I'm with you ... and to be more specific the loss % probably increases slightly as the HP levels go up. As an extremely simple example, the drive train loss % might be 12% at 100 HP, 15% at 400 HP and 18% at 700 HP.
Safety Car
Joined: Oct 2000
Posts: 4,949
Likes: 10
From: Monticello MN
Ed
Last edited by C5XTASY; Aug 19, 2008 at 10:06 AM.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
If you had read my reply, that's what I said. I don't believe that drivetrain loss increases in a LINEAR manner. In other words, it may be 15% with a 350hp engine but a different percentage with a motor of greater, or lesser, power. There's just no way to figure it out without dynoing a motor seperately from the car, and then dynoing with the motor in the car. However, personally, I believe that with higher horsepowers, while total drivetrain loss increases, the percentage of drivetrain loss will decrease. In other words, a 700hp motor will have greater drivetrain loss than a 350hp motor, but not twice as much.
Ed
Ed
So you're saying a drivetrain becomes more efficient as the power going into it increases. I don't think so ... why would it magically become more efficient with more stress on it?
Last edited by ZeeOSix; Aug 19, 2008 at 05:35 PM.
Team Owner
Joined: Sep 2003
Posts: 43,084
Likes: 33
From: Raleigh / Rolesville NC
When you exit one corner or the starting line and lay two black streaks down the track into the braking zone, THAT is right amount.
Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Exactly ... this will give a good date point on the upper end of the HP range. Once the ZR1 dyno HP numbers start coming in, someone could compare 2001 Z06, 2002-2004 Z06, C6 Z06 and ZR1 numbers and determine the percentage of drivetrain loss and if there is a change in the % loss trend with HP levels.
Last edited by ZeeOSix; Aug 19, 2008 at 05:48 PM.