Morgy

As everybody knows more bhp and torque is better but what i'd like to know is whats the difference? Which does what to the cars performance?

Morgy

ne1

bighead

iTrader: (1)

high torque is much better than high bhp figures as its the "torque" that gives you the push in the back feeling

Henrik

iTrader: (5)

It's different aspects of the same thing, really.

Power (bhp) measures the actual "work" an engine can produce.

Torque is a measurement of a twisting force. The torque combined with the rotational speed gives the power, so they're really both interconnected.

It's power available that can be used to accellerate the car, not torque. However, with higher torque at a given RPM, you'll have more power (bhp) available at that RPM, which is why it's nice to drive a torquey engine

Morgy

From whats been said i assume this:

Torque is how much a motor can pull.

Horsepower is how fast it can do it.

Is this right?

Henrik

iTrader: (5)

The horsepower bit is right.

The torque hasn't really got anything to do with how much the motor can pull (apart from the fact that it affects the bhp).

For example, a motorbike which makes say 100bhp at 9000 RPM would exert the same pulling power as a tractor making 100bhp at 500 RPM if both engines were run at those particular RPMs.

NorthDownsScooby

Interesting fact: power (bhp) & torque curves always intersect at 5252 rpm.


Any given car, in any given gear, will accelerate at a rate that *exactly* matches its torque curve (allowing for increased air and rolling resistance as speeds climb). Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it. Torque is the only thing that a driver feels, and horsepower is just sort of an esoteric measurement in that context. 300 foot pounds of torque will accelerate you just as hard at 2000 rpm as it would if you were making that torque at 4000 rpm in the same gear, yet, per the formula, the horsepower would be *double* at 4000 rpm. Therefore, horsepower isn't particularly meaningful from a driver's perspective, and the two numbers only get friendly at 5252 rpm, where horsepower and torque always come out the same.

In contrast to a torque curve (and the matching pushback into your seat), horsepower rises rapidly with rpm, especially when torque values are also climbing. Horsepower will continue to climb, however, until well past the torque peak, and will continue to rise as engine speed climbs, until the torque curve really begins to plummet, faster than engine rpm is rising.

WaltonWRX

iTrader: (4)

Bhp turns heads, Torque turns wheels

Mus

iTrader: (2)

lol

Henrik

iTrader: (5)

I'm sorry, but that sounds like it's completely wrong. Otherwise we'd all be ooh'ing and aah'ing about the accelleration of the farmer's tractors or the lorries that pull stuff on the motorway.

jayallen

iTrader: (31)

BHP sells cars Torque wins races.

NorthDownsScooby

I'm afraid it may sound wrong but that's the physics and the maths of it.

What you are failing to consider is the effect of "gearing" and "power to weight ratios".

Henrik

iTrader: (5)

so why is it a formula 1 car is high revving, low torque? Surely, if it's only torque that is relevant it would be better to stick a diesel engine in an f1 car?

bighead

iTrader: (1)

F1 cars make the power in the higher rpm range (same as Jap supersport motorbikes)than a normal road car , and they are rebuilt after every race
now can you do that to a road car !!
for everyday driving its the torque that counts !!

NorthDownsScooby

F1 cars are a exercise in precise engine design within FIA controlled limits.

I forget what the maximum allowed engine capacity of an F1 car is these days (2.5l..?), but the best way to get 200+mph combined with extreme acceleration is to design the engines to rev high (18,000 rpm). Every car engine designer would be doing this if if we were all prepared to buy £500k cars !!

Diesel engines are not as good for high revving situations.

NorthDownsScooby

ps. a "normal" tractor will make about 100bhp @ a low peak of 2,000 revs. This is the gearing effect I mentioned earlier, and is why most tractors don't (can't) go over 25mph on roads.

borat52

Where did that come from? Its incorrect.
" Another way of saying this is that a car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it."

Thats simply false. The car will accelerate at its greatest rate in any given gear when bhp is at its highest - not torque. In terms of physics you need energy to accelerate anything. Energy is power x time. BHP is a measure of power and hence if you know the energy needed to get a car to 100mph then the higher the bhp (or KW if you prefer metric) the lower the time taken to generate the energy required.

Torque is a component of bhp, so it does have a role in the equation, but an engine producing 1lbft at 1000000000rpm will have 190403bhp and an engine producing 100000lbft at 1rpm would have 19bhp. ie the high torque engine will have very poor aceleration relative to the low torque engine.

Keith Collings

iTrader: (3)

See - Torque - Wikipedia, the free encyclopedia

Henrik

iTrader: (5)

Thank you

W=mv^2 / 2, and W=P*t,

thus P*t = mv^2/2, or t = (mv^2)/(2P). Thus, to accellerate to a certain v as fast as possible, P has to be as high as possible.

rb5_336

some good articles here Puma Racing Main Menu Page - flow development, engine building, technical and tuning articles

Power and Torque 1- How they are related and the maths that explain them
Power and Torque 2 - Output levels for road and race engines, Volumetric Efficiency and improving engine design
Power and Torque 3 - How they are measured, engine dynamometers and rolling road dynos

Mark/WRX

Power sells cars and wins races surprisingly enough.

scoobmeister

Don't think this is strictly true! Whats the point of having a high BHP car that can't put that power on the road, Suspension, Brakes and Tyres are all equally as important,

Mark/WRX

I meant in relation to the question and what others have said.

petedotuk

with my last mods i only improved bhp by 15 but my torque by 39lb ft. what a difference the torque makes

AL99

iTrader: (1)

High torque is important, but it depends where in the rev range you have it.

A lot of typically remapped td04 scoobs have 280 lb/ft of torque - but only at approx 3500 rpm. By 6000 rpm it will be much less, probably down to around 200 lb/ft - hence the power drops down as revs rise.

To keep the torque at 280 lb/ft all the way up the rpm range would require constantly increasing boost pressures. probably over 25 psi by 7000 rpm.
But if you could keep 280 lbft at 7000 rpm then you have a very HIGH BHP car.

low torque honda engines rev very high to compensate.

High torque at high rpm is what really counts.

Flaps

iTrader: (1)

I always thought it was the other way around? Hence the horsepower

JimmyBFC

always go for more torque IMO.

Mine and a friends car are both at 320bhp....mine is 300lbs torque his is 360lbs (2.5ltr bottom end)....lets just say theres a vast difference when we have some fun.....ooooh if only I could afford a bottom end...

Morgy

Ive just had a look at these articles, you're right they are good. I thought my other half might need to know about torque and bhp so i started to tell her, i thought she might be interested, i mean c'mon who isn't. She isn't, she's told me i need to take her shopping to apologise for being so boring

Keith Collings

iTrader: (3)

You have to position it right for her - Torque relates to the amount of shopping carried home and BHP effects the time to get the shopping home - more is better in both cases

Morgy

nice one