Blue_GTO1199

iTrader: (1)

I'm about to do a heads/cam install on my 2000 ss. It's an a4 with an ss3200 and 3.73's. How much rwhp will i need to make in order to have 500 crank hp?

Jake_the_Snake

iTrader: (5)

you're thinking backwards lol. you should be thinking how much crank hp do you need to make to achieve a certain whp. anyways, through a stalled auto, i would imagine around 410-420 whp would make close to 500crank hp. i may be way off, just my non-expert opinion

ex-SS-ve

iTrader: (9)

430 rwhp will get you where you want to be. Your only a set of 220 cc heads and a 232-240 @.610-.630 lift cam and bolt ons away from hitting that number.

Orr89rocz

iTrader: (13)

Typically 15% loss on manuals...sometimes abit less. Autos usually closer to 18-20%. ~400-420 whp should be there

SS SLP2

iTrader: (8)

I think Jake's "non-expert opinion" will be quite close
Johnny

O.N.

Just my opinion here but i dont think it can ever be a percentage loss.

Think about this a 2000HP engine with 15% drivetrain loss =300hp loss
a 500hp engine with 15% drivetrain loss =75hp loss

My opinion is you have xxx amount of rotational mass from the flywheel to the tyres, so thats gearbox, clutch, drive shaft, diff, half shafts bearings, wheels etc etc, it takes xxx amount of force to rotate these moving parts that amount of force doesn't change if you engine makes more power, the same amount of force needs to be applied to make them turn no matter how much or how little amount of power you make.

So my opinion is if it a 100HP loss it will always be a 100HP loss no matter how big the HP is unless you lighten the rotational mass.

Nine Ball

iTrader: (38)

You would be incorrect with your opinion. Here is why. More hp spins these drivetrain parts up to max rpm at a quicker rate of time. The faster the engine has to push these parts to that max rpm, the more energy it consumes to do so. Those rotating parts and drivetrain components do not have a linear friction or resistance, it increases as the time of acceleration decreases. Sort of like how wind drag increases as you go faster. You don't say that wind drag remains constant, do you?

Ravenous T\A

iTrader: (12)

Plus different trannies/rear ends have different amount of loss due to weight of components

Ruthless Robbie

i understand exactly what you mean but you cant look at it that way

you're saying it's an exact number, nineball is saying its a percent..... you're both wrong and both right because its kinda both


if you have a drivetrain that takes 100hp from an ls-1 engine to drive the rear wheels your stating that it wouldn't be a % but an actual number so the 100hp loss wouldn't change


take the ls-1 out and install a 100hp 4 cylinder...... now are you telling me because of the 100hp drivetrain loss that the 4 cylinder wouldnt turn the wheels or move the car??? IT WOULD


and about the percentage loss..... this is true under an acceleration process to where you use more energy quicker causing a higher strain under hard acceleration

but this theory is only correct under full throttle circumstances

because its a measure of power and how quickly that power can turn all those parts in a given time...... this translates into a % loss in the drivetrain


BUT, you cant look at drivetrain loss as an exact % loss because at a constant engine speed the drivetrain loss remains the same no matter how powerful the engine is


meaning you can have a 2,000 hp engine turning the drivetrain at a constant 4,000 rpms and the drivetrain loss will be the same as a 200 hp engine turning the same drivetrain at the same constant rate of speed


simply because its the same friction loss, the same parts, the same drivetrain, the same rate of speed, the same everything...... because of this while the engine is at a constant it will be an exact number instead of a percentage as mentioned above by O.N.


but during acceleration, it is a comparison of power..... meaning even though its the same drivetrain with the same moving parts and the same causes of friction loss....... a 2,000 hp engine would turn the drivetrain at a faster rate than a 200 hp engine

in order to turn something at a faster rate it would take more energy which is lost through the drivetrain.....

so actually the higher the hp = the quicker the turning of the drivetrain

the quicker the turning of the drivetrain = a higher % in used energy aka hp loss







.

SS SLP2

iTrader: (8)

OP I think most of these answers would be a fair "guess about", I do not think any will be 100% correct, are you wanting a "round about " answer or a exect answer ? if so then you will need to put your moter on a moter dyno then back on a roller dyno, or the other way around.
just rambling, Johnny ( sorry about this, just marking time)

Ravenous T\A

iTrader: (12)

I have heard through a transmission like (TH350) mine there is about a 30% drivetrain loss....I like that figure cause that puts me at 600 flywheel

5w20

iTrader: (21)

you n00bs just sit back, ask LMR

1c62nv

iTrader: (3)

Damn, in light of recent discoveries I just found out Im really 600+ hp. woohoo....

B04W

Torque = I * α

...which is what Tony said.

BADMOON

How bout figure out the weight of the car and run it down the quarter and get the mph,instead of dyno racing. Dyno's are like women, they are all unbalanced and different ones say they are somethin they r not...

O.N.

thanks mate thats alot easier to understand, i didn't think of it like that and by the sounds of it you sound correct.

slowredz

iTrader: (23)

HAHAHA so true!

Orr89rocz

iTrader: (13)

Just look at the results alot of guys post on other forums. Alot of engine builders do engine dyno builds and then post their engine dyno values. Some customers will post their RWHP numbers after they isntall the motor into a chassis. From that, its "typical" to see 15-20% loss on most unlocked converter automatics with alot of street engine combos. Thats where I'm deriving my numbers. Its just what I've seen posted and its thrown around the internet alot. Some high stall race style converters may show higher losses.

Like posted above its not an exact % and not really an exact number. It changes on load and rpm. And since all dynos vary to a great degree depending on weather inputs and such, its hard to tell what some rwhp values will equate to at the flywheel/flexplate.

Weight and trap speed is a pretty good way to guess hp too. Old moroso slide rule or whatever it is. It seems to work on the most optimized drag setups...cars that dont ET/mph as well for the power they should be making wont show as much power using this criteria. Most street/strip builds are not as optimized as they should be.

Nine Ball

iTrader: (38)

That is a lot of typing. Nobody said it was an exact figure, these are only approximations which are generally accepted in this industry. The % method is a better approximation, and a fixed value simply doesn't work in this case. The only actual way to measure crank HP is on an engine dyno.

FireHawk178

iTrader: (9)

I just did the calculations and in a vacuum w/air to feed the motor I am making 1900+ RWHP! Keep in mind I'm using Slick 50 that removes all internal resistances. It's also a weightless environment so the reciprocating mass and rolling resistances can be taken out of the equation as well.