Percent or Fixed number?

**Mike0202** · 06-30-2010, 10:44 AM

It seems when ever I read a magazine article reguarding horsepower on a ws6 or any trans am they always take the rear wheel horsepower and simply add 40 hp to determine a crank horse power number. So say the TA puts down 285 to the rear wheels, which is probably the average number. That car would be making 325 at the engine. The way I always used was to take the rear wheel horse power and account for a 12 percent drivetrain loss. An example would be (285/.88=323.8). So both methods are very close but I was just wondering which one would you use?

**shady milkman** · 06-30-2010, 10:55 AM

Originally Posted by Mike0202

It seems when ever I read a magazine article reguarding horsepower on a ws6 or any trans am they always take the rear wheel horsepower and simply add 40 hp to determine a crank horse power number. So say the TA puts down 285 to the rear wheels, which is probably the average number. That car would be making 325 at the engine. The way I always used was to take the rear wheel horse power and account for a 12 percent drivetrain loss. An example would be (285/.88=323.8). So both methods are very close but I was just wondering which one would you use?

i always go 12-15% loss in my calculations. adding 40 does mean shit when you are dealing with engines. a 90hp engine in a kia is not loosing 40 hp. and a 505 ls7 is not loosing only 40.

**TmaxicanA** · 06-30-2010, 01:30 PM

Originally Posted by shady milkman

a 90hp engine in a kia is not loosing 40 hp.

lol but thats probably an accurate HP number would be on a kia.
i think they are generous with there numbers

**Mike0202** · 06-30-2010, 04:54 PM

Originally Posted by shady milkman

i always go 12-15% loss in my calculations. adding 40 does mean shit when you are dealing with engines. a 90hp engine in a kia is not loosing 40 hp. and a 505 ls7 is not loosing only 40.

True but I meant strictly ls1 cars. ls7 would lose alot more.

**9T8W66** · 06-30-2010, 05:45 PM

Originally Posted by Mike0202

True but I meant strictly ls1 cars. ls7 would lose alot more.

For a basicaly stock LS1 car 15% should be approx 40-45 HP.
But there are several variables that can occur to change either the percentage of drivetrain loss or the actual HP the engine is making at a given time.
Weather conditions, Elevation, Regular maintenence and Fuel quality can effect what any car puts to the ground.

**JohnnyBs98WS6Rag** · 07-02-2010, 07:27 AM

Power lost in the drivetrain is purely a function of rotational inertia and viscous friction, which increases with speed, and speed is also a function of how much HP is being driven through it. Thus, a percentage is a much closer approximation to actual drivetrain loss than a flat HP#.

**Y2KPewterSS** · 07-02-2010, 06:21 PM

15% drivetrain loss for manual trannies

20% drivetrain loss for auto trannies

Using 40 HP for LS1s is not accurate.

285 is not an average for LS1s either.

**Mike0202** · 07-03-2010, 05:44 AM

Originally Posted by Y2KPewterSS

15% drivetrain loss for manual trannies

20% drivetrain loss for auto trannies

Using 40 HP for LS1s is not accurate.

285 is not an average for LS1s either.

Maybe not but its the average in the articles I have thats why I used it.

**35th-ANV-SS** · 07-03-2010, 05:54 AM

I'd say about 20-22% loss for my drivetrain.

**Y2KPewterSS** · 07-03-2010, 07:41 AM

Originally Posted by Mike0202

Maybe not but its the average in the articles I have thats why I used it.

285 would be a very low average for LS1s.

**67CamaroRSSS** · 07-03-2010, 12:17 PM

I dynoed my 2002 when it was bone stock so I'd have a way of telling the effect of mods as I did them. It put down 306rwhp and 323rwt. This was on a DynoJet.

**Mike0202** · 07-03-2010, 04:18 PM

Originally Posted by Y2KPewterSS

285 would be a very low average for LS1s.

I think on a mustang dyno 285 would probably be a good number. Not on a dyno jet though.

**35th-ANV-SS** · 07-04-2010, 07:06 AM

Originally Posted by Mike0202

I think on a mustang dyno 285 would probably be a good number. Not on a dyno jet though.

I'm saying that is low even on a Mustang DYNO. I didn't DYNO my car stock, but just with LTs, a lid, air filter, and exhaust I dyno'd 330rwhp and 342rwtq on a Mustang DYNO and that is through a 9" which is a lot less efficient. I would guess you lose about 15-20rwhp with a 9".

**Mike0202** · 07-04-2010, 11:05 AM

Originally Posted by 35th-ANV-SS

I'm saying that is low even on a Mustang DYNO. I didn't DYNO my car stock, but just with LTs, a lid, air filter, and exhaust I dyno'd 330rwhp and 342rwtq on a Mustang DYNO and that is through a 9" which is a lot less efficient. I would guess you lose about 15-20rwhp with a 9".

Depends on the dyno I guess. Most of the ones around here are in the 285-300rwh range. Ive seen a hand full dyno 320 stock but it could have been a happy dyno. Thats why I try not to worry too much about the numbers. Track times is a better indicator imo.

**35th-ANV-SS** · 07-05-2010, 08:56 AM

Originally Posted by Mike0202

Depends on the dyno I guess. Most of the ones around here are in the 285-300rwh range. Ive seen a hand full dyno 320 stock but it could have been a happy dyno. Thats why I try not to worry too much about the numbers. Track times is a better indicator imo.

This is funny coming from someone who started a thread about HP numbers

I agree...take it to the track and see what it does. Two 4th gens: one makes 400rwhp but has stock suspension, stock wheels, stock rear.....runs against a 350rwhp with a fully set-up suspension, rear, drivetrain, trans and DR's. Who's gonna win?

**9T8W66** · 07-05-2010, 10:53 AM

Originally Posted by 35th-ANV-SS

Two 4th gens: one makes 400rwhp but has stock suspension, stock wheels, stock rear.....runs against a 350rwhp with a fully set-up suspension, rear, drivetrain, trans and DR's. Who's gonna win?

This has been my point many times in regards to a plan of attack.
In a Drag race the more powerful car is NOT always the winner.
An engine is only a small part of the setup, a well executed combination of parts will make a faster car.
All the more reason not to get wrapped up in the big numbers game.

**Mike0202** · 07-05-2010, 07:32 PM

Originally Posted by 35th-ANV-SS

This is funny coming from someone who started a thread about HP numbers

I agree...take it to the track and see what it does. Two 4th gens: one makes 400rwhp but has stock suspension, stock wheels, stock rear.....runs against a 350rwhp with a fully set-up suspension, rear, drivetrain, trans and DR's. Who's gonna win?

I wast saying the dyno is completely useless, just debating.

**nomolos1** · 07-07-2010, 05:00 PM

Dynos are different too. A Mustang Dyno is more conservative. A DynoJet gives nicer looking numbers. Not sure which one gives the most accurate numbers. I would rather have a 500 hp car on Mustang, than a 500 hp on a DynoJet.

**Y2KPewterSS** · 07-07-2010, 05:19 PM

Originally Posted by nomolos1

Dynos are different too. A Mustang Dyno is more conservative. A DynoJet gives nicer looking numbers. Not sure which one gives the most accurate numbers. I would rather have a 500 hp car on Mustang, than a 500 hp on a DynoJet.

I would rather have a 375 RWHP car that ran high 11s than a 450 RWHP car that runs mid 12s.

Dyno numbers don't tell you how fast a car is. ETs tell you what a car is capable of.

**shady milkman** · 07-08-2010, 04:49 AM

Originally Posted by Y2KPewterSS

I would rather have a 375 RWHP car that ran high 11s than a 450 RWHP car that runs mid 12s.

Dyno numbers don't tell you how fast a car is. ETs tell you what a car is capable of.

i wouldnt say what its capable of ..a 450rwhp car will have the capacity to run faster than a 375rwhp 99% of the time..of course always depending on the curve and such.