Torque V BHP

[Lone Granger]

I have alway believed that torque / weight gives acceleration - so what do you lose (other than academic top speed) when BHP falls through the floor?

Does a car with 300 lb ft / ton and 300 bhp / ton have same acceleration through usable speed range as one with same torque ratio but 50% power ratio (150bhp / ton) - eg 60-80 mph in same gear with same overall gearing

Another question, if taking above example, you remap torque to 400 lb ft / ton and keep bhp at 150bhp / ton then increase the overall gearing to match extra torque - could you then keep top speed same / increase it whilst maintaing original acceleration?

I.e can playing with torque / ton and gearing achieve similar ends to bhp?

Whicj leads me naturally to strong TDi diesels remapped to limits of airflow, fuelling and turbo capacity - if we are prepared to sacrifice character in our everyday runabout, should we just find a vehicle with a large diesel and tweak it to its limits? - Plenty of c. 3 litre hiflow turbo units to choose from - I understand 330 ft lb from a 2.0d ford is quite possible - I wonder what say a Jag 2.7 is capable of, if over an additional 100 ft lb perhaps we should send Clarkson back to see Sebine?!

[Scuffers]

Power = Torque * RPM / 5252

ie, they are somewhat related.

Performance is all about how much torque an engine has over what rev range, hence why Dismals do really badly, they might have good torque, but only have it avaliable over a limited rev range.

[RobCrezz]

Lone Granger said:

I have alway believed that torque / weight gives acceleration - so what do you lose (other than academic top speed) when BHP falls through the floor?

Does a car with 300 lb ft / ton and 300 bhp / ton have same acceleration through usable speed range as one with same torque ratio but 50% power ratio (150bhp / ton) - eg 60-80 mph in same gear with same overall gearing

Another question, if taking above example, you remap torque to 400 lb ft / ton and keep bhp at 150bhp / ton then increase the overall gearing to match extra torque - could you then keep top speed same / increase it whilst maintaing original acceleration?

I.e can playing with torque / ton and gearing achieve similar ends to bhp?

Whicj leads me naturally to strong TDi diesels remapped to limits of airflow, fuelling and turbo capacity - if we are prepared to sacrifice character in our everyday runabout, should we just find a vehicle with a large diesel and tweak it to its limits? - Plenty of c. 3 litre hiflow turbo units to choose from - I understand 330 ft lb from a 2.0d ford is quite possible - I wonder what say a Jag 2.7 is capable of, if over an additional 100 ft lb perhaps we should send Clarkson back to see Sebine?!

You need a better understanding of Torque and Horse power before you can discuss this further, as it doesnt really sound like you understand correctly.

An engine makes torque, and depending on how many rpms it is doing while making this torque it produces Horse power.

Horse power is the important figure, not torque, because we use gearboxes to transmit this power to make torque at the wheels.

Thats why a 200bhp 150lbft civic is faster than a 150bhp 250lbft turbo diesel.

Power is more important than torque. You need to understand they are related. You cant up the torque without upping the power at the same point in revs. If you up the torque at 2000rpm, you get higher power at 2000rpm. You seam to be confusing this with "peak torque" and "peak power". The reason TDIs make more torque than power is because they cant rev high enough for the high torque figure to turn into huge power.

Edited by RobCrezz on Thursday 29th January 14:50

[Muzzlehatch]

BHP = Torque * RPM / 5252

For good driveability you want high torque for a large range of revs. A tiny powerband (such as in a diesel) is a pain, unless it has very long gearing, but that would then reduce leverage to put less acceleration through the wheels.

Petrol still wins

[LeeThePeople]

Carol Shelby once said torque wins races, horse power sells cars.

There's a lot more to torque than your post suggest, torque has a lot to do with the speed the engine turns over at (rpm) and that gives us the BHP figures. So they go hand in hand to a great extent.

[OJ]

I can't be bothered to write an essay to explain it. It must have been done before, do a search for it

[RobCrezz]

LeeThePeople said:

Carol Shelby once said torque wins races, horse power sells cars.

There's a lot more to torque than your post suggest, torque has a lot to do with the speed the engine turns over at (rpm) and that gives us the BHP figures. So they go hand in hand to a great extent.

Thats true, but if you cant get the torque higher in the revs to produce the POWER then the car will NOT be fast.

150 lb ft at 7000rpm is going to move you much quicker than 200lb ft at 2000rpm.

[Lord Pikey]

So the old saying.

“horsepower sells cars, torque wins races"

isnt strictly true then.

LP

[Nobody You Know]

In terms of "tractable force" BHP is the most important thing.

[OJ]

Lord Pikey said:

So the old saying.

“horsepower sells cars, torque wins races"

isnt strictly true then.

LP

I think the phrase would be more aptly interpreted as 'A wide power band wins races'

[LeeThePeople]

Lord Pikey said:

So the old saying.

“horsepower sells cars, torque wins races"

isnt strictly true then.

LP

No he meant customers worry too much about horse power and race engineers worry too much about torque figures when they need to be considering both.

A lot of race cars are turning to diesel power for torque reasons as well as PR/marketing, being seen to be green etc

[Scuffers]

LeeThePeople said:

A lot of race cars are turning to diesel power for torque reasons as well as PR/marketing, being seen to be green etc

Absolute rubbish.

NOBODY would ever race a Dismal (against petrol) unless the rules are massively rigged (as in Le-Mans) and the marketing dept were paying for it.

put a 5.5L twin turbo V8 in a Pescarolo, and it would inialate the Audi/Peugeot dismals.

[XitUp]

Kinda related - what stops diesel engines revving higher?

[Lone Granger]

I dont see any compelling evidence yet...just the same old, same old ..trotting out that bhp gives better acceleration than torque, I have yet to be convinced that torque isnt paramount within the stated criteria (ie ignoring terminal velocity)

BHP relies on gearing to provide pulling power, whereas torque simply sits there and says 'bring it on..!' - ie Torque needs gears to get high speed and power (bhp) needs gears to create usable acceleration - hence the understanding that it is torque that is fundamental to acceleration, not bhp...

What would happen if you prepared 2 identical 1000 lb vehicles with same linear variomatic transmission, tyres etc and tested acceleration, post tyre slip from same speed to same upper top speed - eg 30-100 mph with differing torques and bhp - I know the higher torqued car would win if both were in top gear, but would they come to some simple eqution when faced with 'infintely' variable gearing and no shift pauses?

I think I would favour the turbo-diesel remapped for hi torque with a high geared vehicle for both performance and economy - and i drive a Griff!

Edited by Lone Granger on Thursday 29th January 15:22

[Kozy]

XitUp said:

Kinda related - what stops diesel engines revving higher?

Diesel doesn't burn quick enough.

[otolith]

Lord Pikey said:

So the old saying.

“horsepower sells cars, torque wins races"

isnt strictly true then.

LP

It's only remotely true when looked at in the context of all of the cars in a given series having similar peak power and revs (which typically, they will have), when the relative shapes of rest of the power curves will become important.

[10 Pence Short]

XitUp said:

Kinda related - what stops diesel engines revving higher?

As far as I'm aware the weight of the internals is a limiting factor.

I seem to remember Honda's engine design guru stating he could easily produce an 8000rpm diesel for road use, but the characteristics of the engine wouldn't match the needs of a diesel engine for road use- MPG and driveability.

[tom g]

Lone Granger said:

I dont see any compelling evidence yet...just the same old, same old ..trotting out that bhp gives better acceleration than torque, I have yet to be convinced that torque isnt paramount within the stated criteria (ie ignoring terminal velocity)

BHP relies on gearing to provide pulling power, whereas torque simply sits there and says 'bring it on..!' - ie Torque needs gears to get high speed and power (bhp) needs gears to crate usable acceleration - hence the understanding that it is torque that is fundamental to acceleration, not bhp...

What would happen if you prepared 2 identical 1000 lb vehicles with same linear variomatic transmission, tyres etc and tested acceleration, post tyre slip from same speed to same upper top speed - eg 30-100 mph with differing torques and bhp - I know the higher torqued car would win if both were in top gear, but would they come to some simple eqution when faced with 'infintely' variable gearing and no shift pauses?

I think I would favour the turbo-diesel remapped for hi torque with a high geared vehicle for both performance and economy - and i drive a Griff!

I don;t think you understand...

"torque" is leverage force from the engine
"power" is the product of torque and engine speed

torque is meaningless without the associated rpm

a diesel with twice the torque and half the redline of a similarly powered petrol will have similar performance, but some will prefer a lazy rattly engine, and others may prefer a screaming one.

ETA: in your example, with infinitely variable transmission, the car with most power will always win.

Edited by tom g on Thursday 29th January 15:28

[BigLepton]

LeeThePeople said:

Carol Shelby once said torque wins races, horse power sells cars.

And then a cleverer bloke said 'Engines don't win races, brakes do'.

[OJ]

Lone Granger said:

I dont see any compelling evidence yet...just the same old, same old ..trotting out that bhp gives better acceleration than torque, I have yet to be convinced that torque isnt paramount within the stated criteria (ie ignoring terminal velocity)

BHP relies on gearing to provide pulling power, whereas torque simply sits there and says 'bring it on..!' - ie Torque needs gears to get high speed and power (bhp) needs gears to crate usable acceleration - hence the understanding that it is torque that is fundamental to acceleration, not bhp...

What would happen if you prepared 2 identical 1000 lb vehicles with same linear variomatic transmission, tyres etc and tested acceleration, post tyre slip from same speed to same upper top speed - eg 30-100 mph with differing torques and bhp - I know the higher torqued car would win if both were in top gear, but would they come to some simple eqution when faced with 'infintely' variable gearing and no shift pauses?

I think I would favour the turbo-diesel remapped for hi torque with a high geared vehicle for both performance and economy - and i drive a Griff!

Power defines how much work the car can do in a given time

Power is work done over time taken

Work done is force acting over a distance

Torque is force applied