bhp and rwhp

[ghetto7o2azn]

Well as u can see on the left side of your screen, i am a newbie. And i got in to cars not too long ago and all the time i see bhp and rwhp. i have a basic idea of what they are but i dont really understand what the difference is. I would be greatful if someone would explain them to me.

[JekylandHyde]

RWHP is rear-wheel horsepower. It is the actual power at the wheels ... how much HP gets to the ground.

BHP is the same as FWHP.
"Brake Horsepower" or "Flywheel Horsepower"... this is the power measured at the engine (at the flyhwheel to be exact).

Because the "power" has to be delivered through the drivetrain (clutch, gears, axles, etc..) there is "drivetrain loss". So RWHP will always be less than BHP or FWHP.

Manufcaturer's usually promote FWHP because it is a larger number. Tuners generally go by RWHP since that is the number that really counts

Example: Stock Toyota MR2 Turbo was rated at 200 FWHP, but in reality it only was getting 165 RWHP or so.

Hope that helps.

[mr2mitch]

but the buety of the mr2 when it comes to drive train loss is it's only a 20% loss to the wheels where as like the supra is like 35-40%.later
mitch

[1ofthesedays]

i heard that most mkiv supra guys dyno around the upper 200hp area, around 260-280rwhp. if you take off 20% of the 320bhp, then you would get aproximately 260hp. i've also heard that toyota underrated the jspec and usdm supra. if the supra actually lost 35%-40% worth of horsepwer through the drivetrain, then that would be more than 100hp lost!

[JekylandHyde]

Drivetrain loss is not a percentage.

[klohiq]

I've heard percentages from magazines and car shows on TV.

[JekylandHyde]

This is my understanding:

It will take X amount of energy to physically move the drivetrain.
X is a fixed rate since the drivetrain doesn't change.
It will take Y amount of energy to accelerate the drivetrain once it is moving.

Y < X

Therefore, as power increases (you add HP to the car)... the "%" of drivetrain loss is less and less.

Pulling numbers out of my butt for example:
If your have a 200 HP with 18% drivetrain loss form the factory you get roughly ...165 RWHP. (This is about right on a 1991 Turbo MR2).

If you now increase the HP of the car to 600 BHP ... you are not going to be losing 108 HP to the wheels through the drivetrain. Make sense?
You might loss ...that initial 35HP + a small amount more.

_________Think of it this way________
If you can push a 100lb weight 10 feet by yourself.... but when I push back against your force, you can only push it 8 feet.
What happens when I double your strength? ... does my strength automatically get doubled? ...no. My force (the force of the drivetrain resistance) stays the same.

[drazhartd]

I love you Jekyl