torque vs revs

[SL666]

it will be interesting to see what CVT transmissions becoming increasingly available will do to the future power delivery of engines..

[The Last Streetfighter]

Yeah. Who needs VVT when you are always at Max Torque...

[SL666]

well on a completely different thought regarding that... imagine only having to tune your engine for the best power and economy in a few different rev ranges.. like the most efficient RPM for cruising, and max hp for acceleration..

[mullett]

Lots of good data...but you kinda mixed up the summary. HP is a mathematical term, but Torque is totally useless when quoted all by itself. Hell, a giant CAT diesel makes killer torque, should I be scared of lining one up? The point is that HP exists as a measurement because you need to be able to apply the torque to the application. If you're trying to do 100km/h, and your engine redlines at 5k, no matter how much torque it's got, it's going to need to be geared correctly, thus removing the torque advantage over a smaller motor which revs harder. My car makes 4000NMatw. Hence why we have: HPatw instead of NMatw. Because that'd just be a game of gearing.

To sum up: As said before, it's all about the torque curve, and the gearing. That being said, I'd put my money on the smaller, revvier motor, as long as it could stay in the RPM range, because it likely has much lower rotating mass.

RM.

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]

Yeah, but there's more friction as you spin faster.
Aye, it's a conundrum.

[mullett]

Agreed, I didn't think about that. Although you've got half as many pistons thrashing around...

RM.

[JustCallMeOrlando]

This is true, but it's still likely to have less friction than the bigger engine at lower RPM. I'm not saying either way, but rather pointing that out.

[Hydra]

I just see it like this - if you have a heavy car then you should probably look at a bigger lower revving more torque engine. Lighter cars can get away with high revving lower torque engines... but high torque engines are good fun anyway.

[oldcorollas]

. Hell, a giant CAT diesel makes killer torque, should I be scared of lining one up? .

ahem..... what do the Super trucks run on a 1/4??? when not speed limited to 160, they do 12 sec 1/4 .. not bad for big truck engines

[mullett]

Hahaha...I'll give you that. Wiseguy...

But, same scenario...they make 1000+HP I wish I had 1000+HP. But then, I DON'T wish my car weight 6tonnes...

RM.

[river]

Hi,

And the R-4360 generated 840ft-lb of torque at 1,000rpm. At max revs of 3,000rpm it generated 7,506ft-lb. The output shaft ran at 1,125rpm when the engine was running at 3,000rpm, and generated over 20,000ft-lb of torque.

Still, it is a big engine - 28 cylinders with a bore/stroke of 5.75inches/6.00inches - with a total of 4,360 cu inches (71.5 litres) , with a compression ratio of 6.7:1.

The carbie was a single four-barrel unit with a throat diameter of 20 inches.




Check out the lovely cut-away pic to see its guts...


Marvellous stuff. I love big piston engines!!!

[myne]

While River shows off his puny little buzzbox, marvel at a REAL lazy, torque monster.

[Draven]

without even opening that link, I'm gonna bet it's that warehouse-sized engine, with a guy standing inside one of the cylinders

[river]

Hi,

Pfftt.... diesel!!!

However, it is mighty big and I lvoe the size of the crank.!!!

You forced my hand now to show the ultimate piston engine.... a thread stopper!!!



Game over. End thread!

nyuk nyuk nyuk

seeyuzz
river

[myne]

Here's a chassis for it to power