How would you calc HP?...
Thread Starter
Instructor
Joined: Feb 2005
Posts: 185
Likes: 0
From: IL
How would you calc HP?...
Mods on 99 A4....3.90s,3200 TC, grizzly LTHrs, K&N CAI, z06 TIT Exhaust
On Dyno Jet it ran 317 RWHP & 340TQ
Now, in a way, this is misleading! (to me at least) Because I know the 3.90s make it a faster car, but shows lower #s on the Dyno Jet. Without the 3.90s I'd be at about 330 RWHP.
SO, using the 15% drivetrain loss....if I am at 317 RWHP, then my FWHP is 373. OR can I adjust for the the "gear loss" and use the 330RWHP to get a FWHP of 388?
Now, if that gets resolved, my next question is does the 3.90s = 50RWHP gain? (Thats what I read here).
My ultimate goal is to figure, with my mods, what equivalent FWHP I have
Is it 317RWHP + 50HP from gears adding DT loss of 15%=432FWHP?
or
Is it 330RWHP + 50HP from gears adding DT loss of 15% =447FWHP?
Help!?
On Dyno Jet it ran 317 RWHP & 340TQ
Now, in a way, this is misleading! (to me at least) Because I know the 3.90s make it a faster car, but shows lower #s on the Dyno Jet. Without the 3.90s I'd be at about 330 RWHP.
SO, using the 15% drivetrain loss....if I am at 317 RWHP, then my FWHP is 373. OR can I adjust for the the "gear loss" and use the 330RWHP to get a FWHP of 388?
Now, if that gets resolved, my next question is does the 3.90s = 50RWHP gain? (Thats what I read here).
My ultimate goal is to figure, with my mods, what equivalent FWHP I have
Is it 317RWHP + 50HP from gears adding DT loss of 15%=432FWHP?
or
Is it 330RWHP + 50HP from gears adding DT loss of 15% =447FWHP?
Help!?
Le Mans Master
Joined: Dec 2003
Posts: 5,561
Likes: 448
From: Atlanta metro Ga.
Because of the way the math works on a DynoJet / inertia-type dyno, yes, a car w/ something other than a 3.42 (or whatever your "stock" gear ratio's are for cars you are comparing to), w/ a higher numerical ratio will dyno slightly lower than one w/ a lower ratio.
And it doesn't have anything to do (o.k., almost nothing) w/ "friction losses" due to the smaller ring gears.
It has to do w/ the way dyno's measure torque, looking at X-amount of work being done over X-amount of time..
The consensus seems to be that 3.90's / 4.10's "loose" about 3% of the actual RWHP dyno recorded value. That's for M6 cars.. A4's are a different animal, and I have no idea. (to clarify, I've seen some really "strange" looking dyno graphs from A4 cars, esp. with aftermarket tq. converters.)
And it doesn't have anything to do (o.k., almost nothing) w/ "friction losses" due to the smaller ring gears.
It has to do w/ the way dyno's measure torque, looking at X-amount of work being done over X-amount of time..
The consensus seems to be that 3.90's / 4.10's "loose" about 3% of the actual RWHP dyno recorded value. That's for M6 cars.. A4's are a different animal, and I have no idea. (to clarify, I've seen some really "strange" looking dyno graphs from A4 cars, esp. with aftermarket tq. converters.)
Last edited by Dan_the_C5_Man; Oct 19, 2005 at 02:48 PM.
Safety Car
Joined: Oct 2004
Posts: 4,816
Likes: 132
From: Plano TX
actually 15% for manual trans and 18% for automatics. Since you have 317rwhp and an automatic you must actually divide by .82 which will put your .18 powertrain loss back to the flywheel. So 317 / .82 =386.5 flywheel hp. This is what you have at the flywheel. As far as adding 50hp for lower gearing. don't know where you got that info, it does make a little difference, not that much maybe 5 hp or 10 at most.
A bone stock LS1 A4 has 287rwhp 287 divided by .82 = 350fwhp. A Mn6 will dyno around 297rwhp stock divided by .85 = 350fwhp
To get rwhp numbers from flywheel numbers for a4 tranny is
350fwhp x .18 = 63 so 350-63 gives you 287rwhp for stock A4
350fwhp x .15 = 53 so 350-53 gives you 297rwhp for stock mn6
A bone stock LS1 A4 has 287rwhp 287 divided by .82 = 350fwhp. A Mn6 will dyno around 297rwhp stock divided by .85 = 350fwhp
To get rwhp numbers from flywheel numbers for a4 tranny is
350fwhp x .18 = 63 so 350-63 gives you 287rwhp for stock A4
350fwhp x .15 = 53 so 350-53 gives you 297rwhp for stock mn6
Last edited by David426; Oct 19, 2005 at 12:41 PM.
Thread Starter
Instructor
Joined: Feb 2005
Posts: 185
Likes: 0
From: IL
Dan: thats 3% loss for the 3.90s sounds right.
I got the 50HP gain from posts on this forum. I know the gears don't actually give more HP...but do make the car faster.
I'm trying to figure out how I can compare my car (w/o going to the track). For example, if my car has 317RWHP and another identical car also has 317RWHP but with 2.73 gears, my car should be faster. Or if another car has 330RWHP and 2.73 gears, my car again should be just as fast, if not faster with the 3.90s.
My tuner said I should have 325-330RWHP with my mods, but the read of 317 was due to the gears. On paper my car may look slower than it actually is. I'm trying to create an "equivalence" factor.
I got the 50HP gain from posts on this forum. I know the gears don't actually give more HP...but do make the car faster.
I'm trying to figure out how I can compare my car (w/o going to the track). For example, if my car has 317RWHP and another identical car also has 317RWHP but with 2.73 gears, my car should be faster. Or if another car has 330RWHP and 2.73 gears, my car again should be just as fast, if not faster with the 3.90s.
My tuner said I should have 325-330RWHP with my mods, but the read of 317 was due to the gears. On paper my car may look slower than it actually is. I'm trying to create an "equivalence" factor.
Melting Slicks
Joined: Feb 2001
Posts: 2,804
Likes: 358
From: Northville, MI
"Mods on 99 A4....3.90s,3200 TC, grizzly LTHrs, K&N CAI, z06 TIT Exhaust"
The only way to find REAL hp/tq is on an engine dyno, the chassis dyno will show what it made that day, based on the skill of the operator. Since GM made 345 hp you can add in another 14-18 hp for the headers. That should bring you up to about 360hp. The gears, CAI, TC will add to the efficiency of the engine and in a real world situation make the car faster, over a given time span. When looking at chassis dyno sheets make sure the graph shows the hp/tq crossing at 5250 prm...you would be suprised at how much hp you can make when they cross at lower levels....
The only way to find REAL hp/tq is on an engine dyno, the chassis dyno will show what it made that day, based on the skill of the operator. Since GM made 345 hp you can add in another 14-18 hp for the headers. That should bring you up to about 360hp. The gears, CAI, TC will add to the efficiency of the engine and in a real world situation make the car faster, over a given time span. When looking at chassis dyno sheets make sure the graph shows the hp/tq crossing at 5250 prm...you would be suprised at how much hp you can make when they cross at lower levels....
Le Mans Master
Joined: Sep 2004
Posts: 7,027
Likes: 6
From: Shiloh Ohio
I have a different approach. Take it to the track is see how much faster it is.
If you want to know HP then take your trap speed and weight and calculate a HP.
Your qtr mile ET and trap speeds (WX corrected) will remain much more consistent than any dyno runs. No matter how you do it dyno or trap speed/weight it is just an estimate anyway.
Off course this could be impractical if you do not drag race.
If you want to know HP then take your trap speed and weight and calculate a HP.
Your qtr mile ET and trap speeds (WX corrected) will remain much more consistent than any dyno runs. No matter how you do it dyno or trap speed/weight it is just an estimate anyway.
Off course this could be impractical if you do not drag race.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
You can calculate you actual rwhp at any moment in time by:
rwhp = vehicle mass * vehicle velocity * vechicle acceleration
where
vehicle mass is in kilograms
vehicle velocity is in meters/sec
vehicle acceleration is in meters/sec^2
Keith
rwhp = vehicle mass * vehicle velocity * vechicle acceleration
where
vehicle mass is in kilograms
vehicle velocity is in meters/sec
vehicle acceleration is in meters/sec^2
Keith
Le Mans Master
Joined: Sep 2004
Posts: 7,027
Likes: 6
From: Shiloh Ohio
Originally Posted by kromberg
You can calculate you actual rwhp at any moment in time by:
rwhp = vehicle mass * vehicle velocity * vechicle acceleration
where
vehicle mass is in kilograms
vehicle velocity is in meters/sec
vehicle acceleration is in meters/sec^2
Keith
rwhp = vehicle mass * vehicle velocity * vechicle acceleration
where
vehicle mass is in kilograms
vehicle velocity is in meters/sec
vehicle acceleration is in meters/sec^2
Keith
Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
Originally Posted by shurite44
Keith give me a practical example of how you do this.
Keith
Le Mans Master
Joined: Jan 2001
Posts: 5,786
Likes: 6
From: Lafayette Colorado
Originally Posted by doubledeuce
I have a 3000 yank stall converter on my 98. Would a high stall converter decrease your powertrain loss?
Keith
Thread Starter
Instructor
Joined: Feb 2005
Posts: 185
Likes: 0
From: IL
No hijacking 
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Instructor
Joined: Mar 2004
Posts: 240
Likes: 0
From: Cupertino CA
Originally Posted by 1999 Vette
No hijacking
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Le Mans Master
Joined: Sep 2004
Posts: 7,027
Likes: 6
From: Shiloh Ohio
Originally Posted by 1999 Vette
No hijacking
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Thanks for the replies. I'm still at a loss for an answer. I'll put it another way...withy my mods, how close of a race is it to say an A4 C6 (stock) which is at 400FWHP.
If you say even race, I would interpret that as my car runs like a 400FWHP car
Does that help, just guesstimates anyway.
