[Mike Edwards]

Okay...

Torque is what engines actually produce: horsepower is a figure of merit (derived by multiplying the torque by how fast the engine was spinning at the time) which allows the output of dissimilar engines (capacity, plus ci vs si) to be directly compared.

Whether your 200hp is better than the 100hp of your rival will depend on the torque multiplication provided by the transmission that connects the engine to the load. Your engine may in theory be better (through having a higher hp figure), but if it isn't matched to the load, the higher hp figure means jack squat.

Whichever Muppet* suggested that forced induction should mean max horsepower at max revs ( it's what your post implies - even if it wasn't what you meant) was talking out of their arse...

*choose your Muppet: Animal, Groucho, Bernie, Miss Piggy....

[NeuroBeaker]

Quote: Originally Posted by Mike Edwards (original)

Whichever Muppet* suggested that forced induction should mean max horsepower at max revs ( it's what your post implies - even if it wasn't what you meant) was talking out of their arse...

*choose your Muppet: Animal, Groucho, Bernie, Miss Piggy....

I'm quite partial to Beaker The Muppet.

And, I agree (for what little that's worth ), I seem to remember glancing at a few dyno readings that certainly suggested that peak HP and peak torque were not at maximum revs in a well-tuned car.


PS
Mii mii mii mii miiii!!!

[Mike Edwards]

The Swedish Chef....

[slim_boy_fat]

Quote: Originally Posted by Mike Edwards (original)

Whether your 200hp is better than the 100hp of your rival will depend on the torque multiplication provided by the transmission that connects the engine to the load. Your engine may in theory be better (through having a higher hp figure), but if it isn't matched to the load, the higher hp figure means jack squat.

Heres the thing 200bhp will always be better than 100bhp, the 100bhp might have more torque (it might not) but even if it does clearly the torque is being produced at a low rpm, otherwise the power would be much higher. So the car that revs higher can use lower gearing, the lower gearing has the benifit of multipling the available torque (lower than the 100bhp car) helping with acceleration

Then again the 200bhp car might have 4 times the torque but its producing its torque at half the rpm than the 100bhp car, therefor it has twice the power, becaue it has t4 times the torque it can overcome the relative lack or rpm and the high gearing required.

This is getting complicated. I need to lay down.

[GTT 280]

would it be useful to introduce some dyno charts with key points explained? Pictures paint a thousand words ;-)

Cheers,
K.

[robbo mcs]

Quote: Originally Posted by slim_boy_fat (original)

Heres the thing 200bhp will always be better than 100bhp, the 100bhp might have more torque (it might not) but even if it does clearly the torque is being produced at a low rpm, otherwise the power would be much higher. So the car that revs higher can use lower gearing, the lower gearing has the benifit of multipling the available torque (lower than the 100bhp car) helping with acceleration

Then again the 200bhp car might have 4 times the torque but its producing its torque at half the rpm than the 100bhp car, therefor it has twice the power, becaue it has t4 times the torque it can overcome the relative lack or rpm and the high gearing required.

This is getting complicated. I need to lay down.

Hi,

Hopefully you have now had a good lie down, and I can produce evidence from the real world to show the benefit of torque

Consider the BMW 120.

In Australian spec they produce a petrol and a diesel. The diesel is slighlty detuned from the euro spec due to heat issues, but that is irrelevant.


According to the the australian website BMW Group Australia

Compare the following figures "

120i (petrol)
156bhp (115kw) @ 6400 bpm
200nm @ 3600rpm
combined fuel efficiency 7.6l / 100km (automatic)
0-100kmh 9.2s (auto)

120D (diesel)
156bhp (115kw) @ 4000rpm
340nm @ 1750rpm
combined fuel efficiency 6.1l / 100 km
0-100kmh 7.8sec

So here we have 2 cars, weighing the same, using the same transmission, built by the same manufacturer. Both make the identical engine horsepower on the engine dyno.

However, the the diesel has heaps more torque, and as a result goes 1.4 seconds quicker in th\e 0-100 (which is an enormous amount when you actually see it side by side). Also as a bonus, the diesel gets 20% better fuel economy

It just goes to show that peak horsepower is only a very crude indicator of the performance of a car. If you are serious about tuning a car for perfomance, area under the curve (torque and hp) is far more important. The example of the 120i and 120d is a prime example. Both would show the same hp on a rolling road, but one would outperform the other in virtually any circumstance

Cheers

Robbo

[slim_boy_fat]

Quote: Originally Posted by robbo mcs (original)

It just goes to show that peak horsepower is only a very crude indicator of the performance of a car. If you are serious about tuning a car for perfomance, area under the curve (torque and hp) is far more important. The example of the 120i and 120d is a prime example. Both would show the same hp on a rolling road, but one would outperform the other in virtually any circumstance

Cheers

Robbo

Your right in your comparison clearly both cars have similar hp figures so the extra torque of the diesel helps, however i am surprised that the difference is so much and would guess that the diesel was a 6 speed manual box with the petrol an auto. This would account for about 1 sec possably slightly more to 62mph.

Also if you extended the acceleration figues to 100mph you will find the gap would be closed and the petrol may have overtaken the diesel.

In real world day to day driving the extra low down grunt of a turbocharges diesel is the way to go, with peak torque usually coming at about 2000rpm or less makes for relaxed high gear overtaking.

[slim_boy_fat]

Quote: Originally Posted by GTT 270 (original)

would it be useful to introduce some dyno charts with key points explained? Pictures paint a thousand words ;-)

Cheers,
K.

Im not entierly sure what help a dyno chart will be but here is one for you to look at.

Its an Ibiza tdi 130PD with a remap.

Shows peak torque at 2600rpm and peak power at 3800rpm.

The car had a great low down kick in first and second gear and would easily keep pace with a friends Leon Cupra R. However once i got into 4th and 5th the cupra would slowly pull on it because of the significantly lower gearing on the cupra which in turn gaive it greater thrust (torque x gearing) in the higher range.

The Ibiza was a bit tricky in the wet too with an open diff and close to 450Nm of torque.

[robbo mcs]

Quote: Originally Posted by slim_boy_fat (original)

Your right in your comparison clearly both cars have similar hp figures so the extra torque of the diesel helps, however i am surprised that the difference is so much and would guess that the diesel was a 6 speed manual box with the petrol an auto. This would account for about 1 sec possably slightly more to 62mph.

Also if you extended the acceleration figues to 100mph you will find the gap would be closed and the petrol may have overtaken the diesel.

In real world day to day driving the extra low down grunt of a turbocharges diesel is the way to go, with peak torque usually coming at about 2000rpm or less makes for relaxed high gear overtaking.

Hi,

You are wrong about the transmission. I deliberately quoted the automatic figures for both cars, as the diesel is only available in auto in Australia.

You can spin the figures whichever way you wish, but I know for a fact that the diesel is 2 seconds per lap quicker around a 4km race track than the petrol, with identical factory bhp

That may surprise you, but it does not surprise me, having looked at the dyno plots for bhp and torque for both cars

I am not trying to push diesel cars. All I am trying to do is point out how meaningless peak horspower figures are as a benchmark in the real world

You could get 2 minis that are both producing 240hp on the dyno, and there could be a big difference in laptimes or 0.60 or 0-100 times

Some of the people on this website just can't get there heads around this Peak horsepower is not meaningless, but it is only a very, very rough estimation of how the car will perform under variable conditions

Cheers

Robbo

[GTT 280]

I assume we are all now knowledgable of what torque is and its purpose .....but are we agreed on the best method of measuring torque?

Is it something we can confidently read from a RR when we also obtain the WHP and BHP?

Cheers,
K.

[Mike Edwards]

Well, given that the torque is what the RR is actually measuring - yes...

[slim_boy_fat]

Quote: Originally Posted by robbo mcs (original)

Hi,

You are wrong about the transmission. I deliberately quoted the automatic figures for both cars, as the diesel is only available in auto in Australia.

You can spin the figures whichever way you wish, but I know for a fact that the diesel is 2 seconds per lap quicker around a 4km race track than the petrol, with identical factory bhp

That may surprise you, but it does not surprise me, having looked at the dyno plots for bhp and torque for both cars

Sorry to disapoint you Robbo but i am well aware of the benifits of Diesel cars, not sure what part of any of my posts gave you the impression i wasnt.

I am just slightly wary when comparing figues between any cars, as the bare figures never tell the whole story, besides you are getting slightly off topic.

Cheers

[slim_boy_fat]

Quote: Originally Posted by Mike Edwards (original)

Well, given that the torque is what the RR is actually measuring - yes...

Agreed most definatly.

To be honest dont get too hung up on this whp and bhp debate which i have kept out of.

The funny thing is both sides of that debate are wrong and both are right it just depends on what way you want to look at the figures.

The thing to remember is when your car gets dynoed then the figues you get for Torque, whp and bhp are specific to that particulare dyno for that particular day.

When you go to nother dyno you will get a slightly different set of numbers, the one number that will be mostly consistant will be bhp, rember i said consistant that does not mean its actually the correct number that the engine is producing.

The only way to properly measure the power and enging is producing is to stick it on a test bed and run it on an engine dyno.

Whp will always be slightly different depending on the dyno.

As will torque obviously because thats what is measured, pwer is then calculated from the torque figure.

This only really matters when you want to bragg about the power and torque outputs using a dyno printout to your mates, what really matters is how the car drives on the road.

[Paul Webster]

Quote: Originally Posted by Mike Edwards (original)

Okay...

Whether your 200hp is better than the 100hp of your rival will depend on the torque multiplication provided by the transmission that connects the engine to the load.

Nice one Mike, I wondered when someone would bring this point up. It was one of the things what I couldn't get my head around in my early years of drag racing but its obvious now

Here's someone elses view on torque;

SEiGHT - Torque vs. Horespower

[Paul Webster]

I've mentioned it before in other threads but with our Mini when we have the ultimate traction with the slicks at the drag strip and let the clutch go between 6k-7400rpm the engine rpm will drop to 1400rpm then slowly`accelerate to 7000rpm where we shift into 2nd.

This is why we have been trying to find the highest trq in that area because this will be the only way at our old weight we will be able to acheive a 12 sec 1/4 mile at 106+

Of course the drag strip is the real world torque dyno.