What effect does torque have on performance? Is it off the line quickness?

My question revolves around how my 05 stock with 210 hp and 240someodd ft/lbs of torque match up against a s2000 with 237 hp and 170 ft/lbs.

 

torque is what carries you off the line, im sure this isnt 100% true but torque is low end power, hp is top end. if you want to take on an s2k you have to consider more than just hp n torque numbers. theyre lighter and i dont know for sure but are probably geared way diff than our v6's.

 

Off the line you would be able to take it, but ,from what I've seen, it's lack of weight will make up for the torque on the topend.

 

that's kinda what i figured. According to the web, it's got 400 lbs less weight and 6 speeds.

 

Torque = acceleration up through the rpm range. Very crudely,

[Acceleration] = [Torque] x [Tranny Gearing] x [Axle Gearing] ÷ { [Tire Radius] x [Car Weight] }

There's more to it, but aside from mentioning that torque does not remain constant over all your rpms that's enough for this discussion.


Only partly. You add a lot to that from flywheel/clutch or torque converter rotational inertia and from torque converter stall ratio, though those effects only exist for very short lengths of time.


You also need to know the weights, gearing, and tire dimensions for both cars in order to be able to compare them. See the above equation.

The S2K has a much higher revving engine (8000 or more), and makes its power way up in the rev range. IOW, it has relatively much better high-rpm torque that works well with numerically higher gearing in either the tranny or the axle or short tires or some of all three.


Norm

 

Thanks Norm.

I can assume from your equation, then, the larger tire radius, the lower performance in the 1/4.

 

Thats an interesting equation. It would help in explanation if it had units to go along with it.

 

I think the key is which engine, over it's use able RPM range, can do more total work.

Even though 250@3500 torque sounds better than 165@6800, it is not even close.

The reason 165@6800 is better than 250@3500 is because the force of the 165@6800 is being applied over a much greater distance ( A factor of 1.94 ). That means that the gearing for the S2000 would be alot better and it would on average produce power nearer to it's peak power.

Don't get me wrong, our engines have alot of torque and that helps them produce great power on average and not just at the peak, but 168 torque at 6800 is going to be very effective for a 230 horespower engine that peaks around 8000.

What it boils down to is that you can calculate acceleration with F=MA if you can figure out the average force that the engine produces. I think it is more likely to approximate the average total amount of work that an engine can do over its rpm range over a period of time, then calculate the total amount of work necessary to accelerate to some speed.

 

Maybe. Tire radius also affects shift points and a couple of other things that I didn't put in the simplified equation above. Basically you'd need to run that calculation for small speed steps where torque and gearing vary accordingly. First gear is likely traction-limited for some or all engine speeds, so you need to keep that upper limit in mind.


ABQ - try this.

[Acceleration (g)] = [Torque (ft-lb)] x [Tranny Gearing (dimensionless)] x [Axle Gearing (dimensionless)] ÷ { [Tire Radius (ft)] x [Car Weight (lb)] }

One g acceleration is approximately 21.9 mph per second.


lundefinedl - it's better if you can model the torque curve rather than use an overall average, as you can then work out incremental accelerations for each mph (or finer, if you're a glutton for spreadsheet punishment). An average taken over a much larger range of speed or engine rpm will give you a general idea what's happening over that range of speeds but won't give you an acceleration curve that reflects the actual engine output.


Norm

 

Norm,

Thanks for the reply. I know what you are saying about torque curves and how this is better than averages; however, I am only saying to use an average as opposed to a peak value to determine performance.

With a torque curve you can fairly easily do a kind of computer simulation that will approximate what would happen, but I'm sure there must be some way to do this more accurately with calculus and physics. The best way to do it I think would be with work and energy as opposed to messing with F=ma.