JohnnyB

See above chip is not a thick cunt

AlexF

WHAT?

to accelerate you need power?????


NOOOOO

Force = mass x acceleration

so you have a car of mass x and you are accelerating at rate y - from somwhere you need a force!!

Torque = force x distance

you need torque to accelerate and nothing else!!!

The result of you having accelerated ie the car is going faster is POWER.

Chip

iTrader: (3)

No alex, you are COMPELTELY missing my point.

Lets say you have 500lbft of torque, but only 200bhp for example.

You will hook up at 1000rpm and by 2000rpm you will have to change gear!

You CANT accelerate hard up the strip without big horsepower, end of, no exceptions!

lead_foot

iTrader: (1)

As far as I see it:

Torque makes it feel fast
Power makes it actually fast.

Good analogy or a load of shite?

Chip

iTrader: (3)

Not really, as you can have less torque and more power, and it will feel faster IF you are in the right gear.

The only reason people think torque matters so much is that they are scared of their gearbox

Turbosystems

iTrader: (5)

bhp = torque x a constant x rpm

foreigneRS

if gearchanging were seamless and instant and you had no limit on the number of ratios, it wouldn't matter (until you get to the speed where drag = power and you can no longer accelerate)

AlexF

Chip,

I know what your saying just mucking around

But your ignoring gearboxes....

Chip

iTrader: (3)

utter rubbish, because everytime you change up a gear, the torque at the wheels (where it matters) drops massively!

Chip

iTrader: (3)

No im not, im not ignoring anything at all, I understand the subject FULLY

The moment you change gear to get back in the power band, you have just REDUCED the amount of torque at the wheels.

Thats why you need the torque to continue up the rev range, which is what then results in more horsepower!

foreigneRS

torque at the wheels only drops massively if you have a massively different gear ratio

Chip

iTrader: (3)

Indeed, BHP is both torque AND rpm in one very useful combined figure.

1/5252 being the constant in the case of bhp and lbft of course.

Chip

iTrader: (3)

And if your gears are only 1% apart, you spend the whole time changing gears, and its STILL dropped massively by the time your speed has increased.

If you are doing 20mph when you change out of first gear on your low revving torquey motor with 500lbft, then by the time you get to 100mph you only have the same acceleration as you would in that first gear with a mere 100lbft if you had the revs to be able to stay in that gear, and you wouldnt have wasted time with lots of gear changes first!

foreigneRS

you wouldn't have lost any time changing gear

if you are comparing doing 100 mph in one gear with doing 100mph with many gears, then you are not talking about the same engine capacity

AlexF

Bingo...

You need torque all the time - low revs, high revs and medium revs

Turbosystems

iTrader: (5)

you are correct chip is not thick

Chip

iTrader: (3)

Unless you are talking CVT, in which case it does t technically class as a gear change, but as a gearing change, you will ALWAYS have "some" time to change gear on a manual box, so its a pointless statement you are trying to make.

Even more so because as the gearing changes, the torque at the wheels drops linearly, where as if you keep the torque constant up the rev range (different boost curve or whatever to do so) then it will accelerate linearly (bear in mind at the same time it will be resisted by air resistance etc though of course so your linear accelerative force wont equal linear acceleation, but that reduction is the same in both cases)

Thats not the case at all by definition, no one has mentioned capacity at all.

Chip

iTrader: (3)

Not true once you are moving, you only need it at high revs as thats the only place you will ever be in a race, well if you can drive anyway, lol

K-NINE

Engine Transmission output torque (ft-lb):
Torque 1st 2nd 3rd 4th 5th
RPM (ft-lb) 3.54 2.13 1.36 1.03 0.72 <- gear ratio
---- ------- ---- ---- ---- ---- ----
1000 50 177 107 68 52 36
1500 65 230 138 88 67 47
2000 80 283 170 109 82 58
2500 92 326 196 125 95 66
3000 104 368 222 141 107 75
3500 114 404 243 155 117 82
4000 120 425 256 163 124 86
4500 125 443 266 170 129 90
5000 130 460 277 177 134 94
5500* 133 471 283 181 137 96
6000 130 460 277 177 134 94
6500* 122 432 260 166 126 88
7000 110 389 234 150 113 79

From a 2.0 ohc engine with a 5 speed box.

Chip

iTrader: (3)

Two simple questions for all.

Anyone with half a brain should be able to see the VERY obvious answers and that should hopefully just end this debate totally, lol



You have a car, it has a CVT gearbox, the revs will remain exactly the same at all times and the gearing will seamlessly vary, its a magical CVT box in that it can do any ratio you want, and it doesnt have any transmission loss to consider.


question 1:
Where on the power curve or torque curve will you set the RPM point the gearbox maintains, for maximum accelration and top speed, is it:
a) at peak torque
b) at peak power
c) where the power and the torque cross

question 2:
If all these engines weight the same etc, which will provide better acceleration AND a high top speed in our car (after the gearbox has been set to optimum for each one):
a) 1,000 lbft, 200bhp
b) 500 lbft, 300bhp
c) 250 lbft, 400bhp


Thankyou, please come again

Nick D

I'm confused

Chip

iTrader: (3)

How did someone so stupid ever end up with enough money to buy all your cool toys, are you a footballer?

AlexF

top top question

Rod-Tarry

My car is fast & it acclerates cos of its flat Torque curve you are only on peak Power once in every gear. Seen dozens of torque less wonders struggle down brunters & not reach 180 telling everyone about their 600bhp no torque shite. Mine held the RWD Topspeed record down Brunters with 480bhp but with 500ft-lb torque.

Chip get back to IT leave this stuff to the likes of Colin Chapman.

Chip

iTrader: (3)

Rod your car was well fairly suited to your gearing at 180mph, with different gearing and 400lbft and 600bhp it WOULD be faster at brunters than with 480 and 500, and Colin Chapman (or even mark shead I suspect, lol) would agree with me on this one

If you are comparing two 500bhp engines, then the one with more torque is likely to have a flatter curve and hence be quicker, but a car with more power and less torque would beat you, thats how physics works.
And by having more power, I mean ACTUALLY having, not claiming, lol

Nick D

I wouldn't consider myself stupid lol

I had a very good start in life, and with a "bit" of hard work it payed off!

Started my company at the right time, and got my first 5 projects off my Dad.

K-NINE

For road,torque is what you want,for racing you need BHP unless you are a restricted rally car LOL.

Simple way of explaining it really.

Stavros

depends what road you talking about and how you drive.

torque is lovely, but any less than about 400bhp isnt enough

K-NINE

Of course,but a normal driver is better off with torque,me i want more torque than bhp on the road.

I have experience of this as i own a german car with more torque than bhp 516ft/lb to be precise,i also own an italian car with more bhp than torque,by far the easier nicer to drive is the german car with limitless power from 2000rpm,the other has to be driven hard which is a bind unless you are on a race track and flat out most of the time.

Mark V8

iTrader: (2)

The reason I'm sticking a 5 litre engine in my Escort is that small engines piss me off, perhaps I'm lazy but ringing the neck of a small engine to get the power of one that is under less strain for the same power level does not make much sense.

Mark

Fast Guy

But they might argue it's torque*revs/5252 (otherwise bhp would always be higher than torque,when in reality it never is below 5252rpm)



Question 1 - I'd actually set it slightly above peak rpm to make use of the available power before it drops off too much.

Question2 - Top speed will be c)
Best acceleration would be a in theory be a), but you'll probably find it weighs well over 7.5tonnes and is limited to 56mph (1000lbft at 1050rpm that's a big engine, what's the rest of the power curve like?)
On the road b) would be the best all rounder as it has good midrange
On the track I'd probably fancy c) as it has good torque high up.



The simlpe answer to this is----

Most (highly tuned cars excepted) have max torque lower down in the rpm range say 3.5-4.5Krpm Max power can be from say 6200rpm upwards on 16V motors.

Take your car down the drag strip and do 2 runs.
Run1 change gear at your max torque rpm
Run2 Change gear at your max power rpm.

See which is quicker down the strip. I know which one I'll put my money on.


Where does any car make it's theoretical top speed? at the Max power rpm or max torque rpm? (still assuming optimum gearing for top speed)

K-NINE

You should always change gear at max power RPM.

AlexF

Even mid bend

POPEYE

I like the low down grunt of my car, makes 483 lb/ft
Revs quite well for a V8 i thought, got bloody long gearing though, does about 80/85mph in second. Wouldn't mind changing the rear diff to 3.9 or 4.11

COCHYN

BHP sells cars, TORQUE makes them go

4x4

ah ha thanx for that, thats summed it up a treat... Why chip and the others couldn't put their scenarios in such an easy way is beyond me... subject solved, thread closed, we can all go home

Chip

iTrader: (3)

Fastguy, totally incorrect answer to the second one.

C would be the highest top speed and C would be the fastest acceleration

Chip

iTrader: (3)

Other than the minor fact that what he put is of course total bollocks, but thats a small point as at least it was catchy and short

Chip

iTrader: (3)

utter utter bollocks.

Typically to maximise acceleration you change up shortly after peak power, if you change up at peak power, the revs will drop too far going into the next gear and you wont be back on it hard enough, so you rev past.

If you want to get slightly technical, you should plot the torque curve multiplied by the gearing out for each gear, and change just ever so slightly after they cross.

Typically its about 500-1000rpm past peak power, but that really is a huge generalisation of course.