Tubby Vs New Audi RS4 (420bhp)

[^Trickster^]

Torque does not matter??? I can even believe that deserved a reply.

Its ok lads, tyres dont matter, just run it on the rims!

Graeme

[skinthespin]

power is just a function of torque and revs, like Bibbs said, its all about the shape of the pwer/torque curve, for gods sake buy Issue 3 of mr2only, I explain it all in there!

[Andy Champ]

I can understand how it would make you think torque doesn't matter when you list the 2 examples above. The only problem with that is the 2 values you mention are only the peak torque and peak power values. You cannot guess the car's acceleration with this alone - you would need the whole torque and power chart - these would tell you the torque curve and where and for how long a certain level of torque in the RPMs occured, as well as the max RPM for that engine.

Here is a really good webpage which explains it a lot more clearly than some others on the net:

http://www.boostaholic.com/hptq.html

I think it's a really good read

Great link, thanks for that. I've a feeling I've seen the one about the waterwheel before.

I'm quite aware that it's the area under the graph that matters, but I haven't any more data available than torque and power peaks.

Poor examples Andy, for the reasons given above.

And that statement in bold, is definately not correct.

Two cars can make exactly the same peak horsepower, but one may make more torque at a lower given RPM, and will therefore accellerate more quickly to a given speed.

Point in fact: Top Gear did a thing about the Evo 8 FQ400. It raced a normal family hatch (Focus I think), and was flayed alive, as the hatch sped away due to it having more low down torque. When the Evo's big turbo eventually woke up, the FQ shot past the hatch on a wave of...

...you guessed it,

TORQUE!

Now the Evo made 400bhp. The hatch, probably made something in the region of 150bhp but it was able top pull away. Explain that one.

EarL.

The EVO vs the hatch? I don't need to explain it, you did. Well, mostly...

"When The Evo's big turbo woke up" - how much power was it making before then?

Let me give you guys some more to think about, now I've got your attention.

First: In order to make something accelerate, you have to apply a force. That's Newton's physics, F=MA. Or more interestingly the simple transformation A=F/M. This states that the acceleration is the force divided by the mass. So a light car, or one able to provide more force (not torque, nor power) will accelerate faster. Are you all with me so far?

Second, the way you get force with a wheel driven vehicle is to apply torque to the driving axle(s). Aha! I hear you cry, he admits he is wrong.

Not so!

I can vary the torque applied to the back wheels of my '2 in several ways:

I can put the brakes on (silly under the circumstances) slip the clutch (only useful when first gear isn't low enough) open the throttle (which will be fully open, if I'm accelerating hard) - or I can change gear.

You all know, if you think about it, that lower gears give more acceleration. (At least for a bit). Pick say 3000 RPM; in first, floor the throttle. Neck snapping stuff. In 2nd, fairly brisk. In top - stuff all. That is because the torque has varied at the wheel.

You'll also all know that you can't do 0-60 in 1st - at least not in a '2, although the FQ in that Top Gear program might. That's because you run out of revs.

It's those two together - the revs times the torque - which are the power output of the engine. It is that ability to put the torque out at speed which allows the car to accelerate.

That little hatch might hold the FQ at first, but only because its first gear will be set to run at much lower speeds than the FQ. That lower gear will result in a similar force at the wheel from the far lower power (and torque!) output.

Andy

[Scotster]

I can understand how it would make you think torque doesn't matter when you list the 2 examples above. The only problem with that is the 2 values you mention are only the peak torque and peak power values. You cannot guess the car's acceleration with this alone - you would need the whole torque and power chart - these would tell you the torque curve and where and for how long a certain level of torque in the RPMs occured, as well as the max RPM for that engine.

Here is a really good webpage which explains it a lot more clearly than some others on the net:

http://www.boostaholic.com/hptq.html

I think it's a really good read

Great link, thanks for that. I've a feeling I've seen the one about the waterwheel before.

I'm quite aware that it's the area under the graph that matters, but I haven't any more data available than torque and power peaks.

Poor examples Andy, for the reasons given above.

And that statement in bold, is definately not correct.

Two cars can make exactly the same peak horsepower, but one may make more torque at a lower given RPM, and will therefore accellerate more quickly to a given speed.

Point in fact: Top Gear did a thing about the Evo 8 FQ400. It raced a normal family hatch (Focus I think), and was flayed alive, as the hatch sped away due to it having more low down torque. When the Evo's big turbo eventually woke up, the FQ shot past the hatch on a wave of...

...you guessed it,

TORQUE!

Now the Evo made 400bhp. The hatch, probably made something in the region of 150bhp but it was able top pull away. Explain that one.

EarL.

The EVO vs the hatch? I don't need to explain it, you did. Well, mostly...

"When The Evo's big turbo woke up" - how much power was it making before then?

Let me give you guys some more to think about, now I've got your attention.

First: In order to make something accelerate, you have to apply a force. That's Newton's physics, F=MA. Or more interestingly the simple transformation A=F/M. This states that the acceleration is the force divided by the mass. So a light car, or one able to provide more force (not torque, nor power) will accelerate faster. Are you all with me so far?

Second, the way you get force with a wheel driven vehicle is to apply torque to the driving axle(s). Aha! I hear you cry, he admits he is wrong.

Not so!

I can vary the torque applied to the back wheels of my '2 in several ways:

I can put the brakes on (silly under the circumstances) slip the clutch (only useful when first gear isn't low enough) open the throttle (which will be fully open, if I'm accelerating hard) - or I can change gear.

You all know, if you think about it, that lower gears give more acceleration. (At least for a bit). Pick say 3000 RPM; in first, floor the throttle. Neck snapping stuff. In 2nd, fairly brisk. In top - stuff all. That is because the torque has varied at the wheel.

You'll also all know that you can't do 0-60 in 1st - at least not in a '2, although the FQ in that Top Gear program might. That's because you run out of revs.

It's those two together - the revs times the torque - which are the power output of the engine. It is that ability to put the torque out at speed which allows the car to accelerate.

That little hatch might hold the FQ at first, but only because its first gear will be set to run at much lower speeds than the FQ. That lower gear will result in a similar force at the wheel from the far lower power (and torque!) output.

Andy

Finally i've read a post from you i 100% agree with. You will notice though that if you take everything you said and pitch it to the 350bhp MR2 vrs the M6 that what you said initially doesn't quite hold up.

Scott =op

[Leon.]

Its also worth remembering that it takes a massive power differential between cars to make another car look like its going backwards.

Exactly.

Andy champ, so you say torque doesn't matter, then you copy a previous poster's physics equation of hp = rpm x torque/5,252. It is clear that both influence one another. Why not admit you were wrong

[Bibbs]

Torque is the only thing you feel and the only thing you can measure on a dyno.

BHP is then obtained from this, by using the speed/rpm.

Dyno's measure torque and rpm, and calculate BHP. Then with smoke/mirrors/thin wires and guesswork you get the pointless flywheel bhp.

And the EVO was beaten by the hatch, as off boost the car has so low compression and so much turbo lag the output from the engine was pathetic.

[Scotster]

Torque is the only thing you feel and the only thing you can measure on a dyno.

BHP is then obtained from this, by using the speed/rpm.

Dyno's measure torque and rpm, and calculate BHP. Then with smoke/mirrors/thin wires and guesswork you get the pointless flywheel bhp.

And the EVO was beaten by the hatch, as off boost the car has so low compression and so much turbo lag the output from the engine was pathetic.

It was a fiat something or other and they both went into 6th gear at 30 mile per hour.

The evo is geared to manage 180 or so MPH @ max revs the fiat is probably geared for 150 or so mph @ max revs. Not only is it heavier, off boost and at the lowest point of its torque curve but it also needs more force to actually turn the wheels due to the gearing and the fact that its 4wd.

On a bike its like trying to accelerate from 5mph in 21st gear against someone in 15th. Granted once you get to a certain speed you will fly past them as the evo would have had jeremy not lied and said they were out of runway.

Scott =op

[Bibbs]

http://video.google.co.uk/videoplay?doc ... 0846526727

6:45 in ..

If you can't wait for it to download all of it, move the slider and it'll buffer from there foward.

Low compression engine, low revs, BIG turbo

[The-Shield]

It was a fiat something or other and they both went into 6th gear at 30 mile per hour.
Scott =op

From memory it was a diesel Skoda Fabia

**edit** I tell a lie, it was a 1.6 Fiat Stilo (estate?)

[Scotster]

Yeah, estate rings a bell actually.

The fabia was VS the cooper.

Scott =op

[Andy Champ]

You will notice though that if you take everything you said and pitch it to the 350bhp MR2 vrs the M6 that what you said initially doesn't quite hold up.Scott =op

.. and you'll notice I pointed out there were 2 MR2s in the thread a few days back, and said I wouldn't want to call the win with the 350BHP one.

Torque is the only thing you feel and the only thing you can measure on a dyno.

Aren't some dynos flywheel based? They deduce power and torque by measuring the change in rotational inertia over time.

Andy champ, so you say torque doesn't matter, then you copy a previous poster's physics equation of hp = rpm x torque/5,252. It is clear that both influence one another. Why not admit you were wrong

Well apart from the fact I think in Newtons Watts and Kilos - then do a last-moment conversion to HP which everyone has a feel for - I stand by that rather inflammatory statement.

I have not a clue what the torque at my flywheel feels like. I couldn't even tell you what it is, in any units.

I do know that what makes the car accelerate is force at the wheels, and this is produced from the engine power working with appropriate gearing.

I can also know that you cannot get power out of a rotating type engine without torque. But it isn't the torque that matters, it's the power.

The torque figure to me is useful for only one thing. Peak torque at 2000, peak power at 6000 implies a big wide power band. Peak torque at 3000, peak power at 4000, you'll be forever changing gear. What I really want is the width of the power curve at some percentage of full power - 80% say. For all engines. But no-one publishes that.

Last thought - what's the torque of a jet, or a rocket? They sure as heck make things accelerate!

Andy

[Leon.]

But its wrong to say torque does not matter, since power is a product of torque and rotational speed (of the engine).

Horsepower is defined as 33,000 lbs.ft/minute - defined by Watt originally based on the work of 1 horse over this time. This comes from Power being the expression work done / time, or torque / time.

After some serious maths and as already mentioned this equats to:

Horsepower = [torque x angular speed (RPM)] / 5252

In terms of gearing, power is dictated by how well the gearing of the drive train utilises the available torque. As the rotational speed of the engine (RPM) increases, torque will decrease after a cetain level due to an increase in friction and other constraints. The drive train etc therefore dictates the hp derived from torque.

FWIW and a bit off topic, but torque is commonly written as lb/ft, esp. by people on here. This is incorrect as it denotes mass divided by distance which is wrong. It should be written lb.ft, i.e. mass multiplied by distance.

[Scotster]

............
I do know that what makes the car accelerate is force at the wheels, and this is produced from the engine power working with appropriate gearing.

This is where i think wires are getting crossed. Don't think of engine power as BHP. The power of the engine is the amount of force it turns the flywheel with hence torque.

I can also know that you cannot get power out of a rotating type engine without torque. But it isn't the torque that matters, it's the power.

I dunno if i'm banging my head against a brick wall here but power is measured in watts, right or wrong?? How many watts does an engine produce and wtf has that got to do with a car accelerating? Ok, take the word "power" out of the equation. What makes the wheels turn... answer torque. What makes the flywheel turn... answer torque. There is no measurement of power that can be taken here other than a commonly known measurement called BHP which is a calculated figure. People always think of power due to BHP but thats not what actually turns the wheels and makes the car acclerate.

Last thought - what's the torque of a jet, or a rocket? They sure as heck make things accelerate!

Ahh now were talking, i'm a mechnical engineer for an aerospace company. Thats actually measured in thrust as its not torque from the engine that powers it. I can assure you that it isn't bleeding BHP or your rendition of "power" either although i guess this could be calculated if you measured the torque the engine produced at a certain amount of revs.

Now, you said that your into laws of physics etc. Can you tell me which law of physics has power in it with regards to rotational mass and without measuring electricity? Granted i only studied physics at higher level but i don't remember anything being covered here other than work done.

Scott =op

[Andy Champ]

Ahh now were talking, i'm a mechnical engineer for an aerospace company.

Well F*** me I wish you'd said that 20 posts ago, I was trying to make things simple! (and obviously failing!)

To accelerate I need to increase the kinetic energy of the car. That's Joules (in the metric world) and since I want to do it quickly, I want lots of Watts.

Does that make sense?

Andy

[Scotster]

Yup makes perfect sense. The potential energy of the car is in the petrol. The petrol ignites in the car causing kinetic energy in the pistons and the conrods which turn the crank. The kinetic energy turns into force which is known as Newtons. The force with which the crank turns is measured over the distance of the crank known as NM and this can be translated into ftlbs which is torque. The torque turns the flywheel which in turn turns the gearbox which in turn turns the dif which in turn turns the wheel. There will be a loss of torque from the fly to the wheel etc.

But, the power of the car is the amount of potential energy turning into kinetic energy as every single car will be different. Not just makes and models but little differences in the car. Thats the reason a cars "power" is measured in torque and then the BHP is calculated from that. BHP doesn't have anything to do with the true meaning of the word power though.

I am curious. Some cars have an actual KW power output on the graphs. That may be the actual power the car generates which would make a difference.



I just said i don't know much about cars

Scott =op

[Leon.]

I'd say that's pretty spot on, from what I understand anyway...

[EarL]

Yup makes perfect sense. The potential energy of the car is in the petrol. The petrol ignites in the car causing kinetic energy in the pistons and the conrods which turn the crank. The kinetic energy turns into force which is known as Newtons. The force with which the crank turns is measured over the distance of the crank known as NM and this can be translated into ftlbs which is torque. The torque turns the flywheel which in turn turns the gearbox which in turn turns the dif which in turn turns the wheel. There will be a loss of torque from the fly to the wheel etc.

But, the power of the car is the amount of potential energy turning into kinetic energy as every single car will be different. Not just makes and models but little differences in the car. Thats the reason a cars "power" is measured in torque and then the BHP is calculated from that. BHP doesn't have anything to do with the true meaning of the word power though.

I am curious. Some cars have an actual KW power output on the graphs. That may be the actual power the car generates which would make a difference.



I just said i don't know much about cars

Scott =op

Hooray!!! Well done Scott. That's a pretty spot on explanation mate.

[Bibbs]

I am curious. Some cars have an actual KW power output on the graphs. That may be the actual power the car generates which would make a difference.

1kW = 1.341bhp

So it's nothing but the metric equivalent to bhp
(as Nm is to lbft .. lbft * 1.3558 = Nm)

[ben25]

Its all about power to weight ratio. When I had my ZR Turbo that was 260bhp and would eat new E46 M3's for breakfast yes the M3 would have had about 90bhp more but also twice the weight. Also raced a 380bhp Impreza down the strip at Santapod he done me off the line but halfway down the straight when I managed to get traction I flew past him

[Scotster]

You need to read this whole thread mate. Its about power to weight but not BHP to weight. Acceleration will be mostly down to Torque@Revs to weight.

Thats what the whole discussion has been about.

Scott =op