Bhp

[Trevz]

I thought bhp was measured at the road wheels.

My mate (who's always right) says its measured at the crank, so the bhp measured on a rolling road would be alot less than 300 for a tt Z.

Is he right again? :rolleyes:

[SRRAE]

When you get a BHP for a car it us the power at the crank, which really is usless. The real power is WBHP which is Wheel Brake Horse Power or RWBHP Rear Wheel Brake Horse Power. This is the power which actually makes it to the ground and causes you to move.

 

The Nissan 300ZX is said to have 300bhp but only 240-280 will reach the wheels depending onthe type of transmission and the condition of all the parts.

 

Car companies always tell you the power at the crank because it sounds better, and different things like different transmissions will cause different BHP at the wheel even though they have the same engine.

 

You can increase the RWBHP by making the drive train more efficient. Lighter flywheel and straight cut gearbox (For manuals) will increase power to the wheels even thought the engine power is the same.

[SRRAE]

The more the power has to travel and change direction it loses power.

 

So a 300ZX will lose power in the fly wheel, clutch plate, gearbox, propshaft, diff, drive shafts and so on.

Usually installling a lighter component will make it more efficent so a lighter flywheel will make less power is lost in the flywheel. A lighter propshaft means less power lost in the shaft, which means more power at the wheels.

 

4 Wheel Drive systems lose a lot of power, becuase there are more diffs and the power has to travel a long way. I have seen a dyno of a stock R34, which had 278bhp (0r something) at the crank and only 202bhp at the wheels.

 

Front wheel drive cars and mid/rear engine rear wheel drive cars lose the least power, because the power doesnt have to travel far to rear the wheels.

 

I have seen a MR2 Turbo with stock power of 245bhp, it had an induction kit and HKS exhaust and it has 245bhp at the wheels, because very little is lost in a rear engine rear drive car.

 

 

Stuart

[tinkywinky]

Car companies always tell you the power at the crank because it sounds better, and different things like different transmissions will cause different BHP at the wheel even though they have the same engine.

 

Not strictly true SRRAE

 

For a car company to quote any power figures the figures have to be certified.

 

This is done by an independent institute that is recognised by the governing body of motor vehicle manufacturers ( forget what there called ).

 

As to pass this power cert any unit must be within 5% of the claimed power output, it's logical to go as far up the drive train as possible, i.e. engine, as any losses are easier to compensate for here.

 

I've built lots of power cert engines and you wouldn't believe how close to the edge some manufacturers run engines just to get their power cert figures.

 

Cheers

 

Robin

[Paul C]

BHP is just a measurement, i dont know why quoting crank bhp would be useless, all manufacturers do this. RWBH will obviously be lower.

 

it is a measurement of the power of the engine. thats it.;)

[Trevz]

cheerz guyz

so, he's right again :rolleyes:

[Guest Jezz_S13]

wheel power or even, wheel power/weight would be better than fly figure.

[Guest 300z]

Is it not true manufacturers get engine power on an engine dyno?

well errm actually it is true lol.

so the difference is alot.

people or independant places always tend to quote flywheel power as its a projected figure and is always edged a little higher with percentages ect.

Wheel BHP is where its at :D

[paulg]

Remember peak power (which is always quoted) means nothing when it comes to acceleration. You are only up there for a split second before you change gear, a zed could have 50hp less than another and still out accelerate it if it makes more torque lower down the rev range.

[chopper]

well im confused!!!