torque vs revs

[love ke70]

hi guys, was just thinking about a few things and i came up with a litte scenario to better explain it:
lets take a v8
and a vtec motor from a honda s2000 or any motor that revs along way
they both make the same horsepower.
one makes this power due to large torque, the other due to high revs
lets put them in chassis' which when the engine is added they both end up weighing the same.
and we line them up, which is faster?

now the logical answer i come to is the v8 will beat it hands down. however im not sure. and i dont know the reasoning behind my answer
so im just after some opinions etc.
cheers, andrew

[JetspeedCamry]

Well the way i think of it is....

V8 will pull away off the line...
the gap between them will start to equalise as the S2000 approaches hi revs/peak power.

Perhaps the V8 may run out of puff in top end speed...so then the S2000 would start to become equal and pass...

Depends on a few things like traction too..but, id imagine if the S2000 tried to start off in its peak power RPM (hi revs/drop the clutch), then it would simply burn the tyres..

[oldcorollas]

lets NOT start this again.

to summairse all the previous threads in one hit.

IF the car weight was the same,
IF the power was the same.
IF the torque curve was the same shape,
and IF gearing was such that both motors redlined at the same car speed in the same gear..

THEN they would have the same acceleration.

neglecting many factors.. btu thats the basic maths

[love ke70]

left me with nothing to argue with lol
spose it is all in the gearing

[myne]

That's why horsepower is still a relevant number despite still being a fairly abstract concept.

The concept of horsepower is "Work done over time".

Torque is merely a measurement of twisting force.
My leg probably has more torque than my engine but there's no way it can outperform it.

[Earlyrolla]

hi guys, was just thinking about a few things and i came up with a one makes this power due to large torque, the other due to high revs
cheers, andrew

Don't get confused between power and torque.

The amplitude of torque depends on the downward force of the con rod which in turn depends on the pressure applied to the top of the piston during combustion. The more air/fuel mix the engine burns in one combustion event the higher the resultant torque on the crankshaft. This maybe the case in a supercharged small capacity engine application where the piston size remains the same but the mass of air/fuel is increased in the cylinder thus increasing the in cylinder gas pressure OR alternatively on a larger naturally aspirated engine burning the same mass of air/fuel as the small engine at a lower in cylinder gas pressure that is dispersed over a larger piston top. This is because Force = Pressure * Area. Thus increase either pressure or area (or both) to increase force and in turn torque on the crankshaft.

Power is a measure of energy over time. Each combustion event chemical energy is converted to mechanical energy. So therefore the more combustion events you can have per second the more power your engine will make. Obviously there are many other factors involved like air flow characteristics and frictional losses etc. Ideally the harder you rev an engine the more power it would make. That is why a small engine revving hard (say 3000 to 4000 RPM more than a V8 will produce the same power as the V8).

If you ready knew all this then great

oldcorollas summed up the race thing pretty nicely.

[Dimmy]

the way i think of it is, the motor with more torque will be quicker off the line wheras the motor with more power up the rev range would beat the torquier engine over a longer "race"

Torque and power are not the same thing, think of torque as the 'pulling power' of the car off the line and the pwer is it's peak power at a certain RPM (higher rev range)

sorry about my shitty post but my brain has shat itself from uni

[Draven]

and never make the mistake of thinking that peak power (or torque) figures mean much of anything in terms of performance of a car. it's the torque *curve* which dictates acceleration.
other than that minor expansion, stu has put it perfectly.

[Nark]

Area underneath the torque curve FTW!

Anyone remember their differentiation and integration? dy/dx...

[urantia]

Out of curiosity, who'd likely win a 1/4 mile between a stock motor 7mgte ma60 and a stock jza70 both manual. (yeah strange question, jsut curious if anybody may know)

[JustCallMeOrlando]

Off topic, but providing they're both healthy and both get a similar launch you'd expect them to be fairly similar at around mid 14's.

[urantia]

Interesting, thanx, and I'll let you know the outcome
(/back on topic)

[The Last Streetfighter]

Plot a curve of Torque Vs Revs for each car. (Most of the answers are in this curve!)
Torque in Newton-Metres and Revs in RPM.
Now comes the maths and kinetics/kinematics:
Power (in a straight line) = Force / Time = Force x Velocity (P= F/t = F x v)
Power (in a circle) = Torque x Rotational Speed (P = T x w (w is omega, radians per second))
Now convert RPM to Radians per second. There are pi (3.14) radians in 180 degrees and 60 seconds in a minute. So 1 RPM = 2 x pi / 60 Radians per second.
So take any number of points on your Torque vs RPM curve and translate the Torque at instantaneous RPM's to Power at RPM's by P = T x RPM x 2 x 3.14 / 60
Now plot these points and you have a Power curve.

If you have done this correctly you will see a few things:
1: The V8 makes heaps of torque and more power down low than the small displacement engine.
2: You will see what we mean by, "Area under the curve" or, "Useable Power"
3: Torque is important. Power is purely mathematical! Get over it.
4: At the top of the page I highlit the word "most". That is an indication to where Stu has referred to things like gearing and diff ratio.

Trev

[myne]

2 engines. One revs 3x faster but produces 1/3 of the torque.
Both have identical power at comparable intervals.
Both are equal.

[The Last Streetfighter]

I should also add that Rotating Masses (Flywheel, crank, cams) will not affect (noticeably) Power, but will significantly affect Pickup (acceleration). They are the unseen vampires sucking the blood from your 1/4 mile times and not showing up on the dyno. Reciprocating masses (con rods, pistons) suck power and pickup...