Destiny2002

Destiny2002

Destiny2002

ttb

hope this hasn't been posted already

http://www.yawpower.com/tqvshp.html

explains why torque is meaningless with gearing and rpm

no really

That article is

They compare a diesel truck engine and a F1 engine with very different power levels, with transmissions geared to hit 200 mph at redline in 5th gear, because that is what the F1 engine can do well. They should have geared them to hit 60 at redline in 3rd gear towing 10 tons, because that is probably pretty close to what the diesel engine can do well. The F1 engine would lose that race. That hardly means anything.

Why didn't the author compare two engines with the same HP numbers, but different amounts of torque? Then, you can gear them the same, and see which accelerates fastest. If you use different HP, different torque, and different gearing, you allow too many variables into the equation to make use of the conclusion.

Consider, I have two buckets. Bucket A is 240 centimeters (hp) across, and 153 centimeters deep (tq). Bucket B is 240 centimeters (hp) wide, and 320 centimeters (tq) deep. Which bucket holds more water?

A S2000 and a 350Z run fairly close in a race. The 350Z has alot more torque, alot more weight, and alot more HP. The Mustang GT is also close. The GT has the same weight as the 350Z, less horsepower, but alot more torque. It has more HP and twice the torque as the S2000. Why do these cars run so close if HP is the only important number? Weight is an issue, but at only 20 HP down on the GT and 400 pounds lighter, the S2000 ought to be much faster than the GT if torque truly did not matter. If HP was all-important, the 350Z would pull pretty hard on the GT and the S2000.

Gearing and torque are really the most important factors here. The S2000 has a steep rear gear for better acceleration, while the GT has a comparitively high final drive gear. If the two cars had the same gearing, the GT would be faster. I really don't know what the rear gear in the 350Z is, so I can't comment.

Horsepower is just a way of stating the amount of torque at a given rpm. It is commonly used to refer to the peak number TQ * rpm / 5252. This allows one to roughly compare the output of different engines. It is not an absolute predictor of performance. There are many variables that come into play with a car's acceleration rate. HP is useful as one number of many, not as the only number.

Destiny2002

AbusiveWombat

I'm not even going to read all 13 pages.

hp = tq * rpm / 5252

without torque there is no horsepower. You can not say one is more important than the other.

A torquey engine, like the Mustang GT, has more horsepower in the lower rpms because it has more torque in the lower rpms. Hence it accelerates faster in the lower rpms. the S2000 is a dog in the lower rpms because it has low torque...which leads to low horsepower but the S2000 is able to hold that torque out to a very high rpm...which leads to good horsepwer and good acceleration.

It's a very simple formula with two different ways to make horsepower.

A.) more torque = more horsepower (Example: Mustang GT)
B.) more rpms (torque being constant) = more horsepower (Example: S2000 or RX8)

In the end acceleration is dependant on 2 things...horsepower and weight.

FCGuy

... and it continues ...

The recently referenced article is 100% correct from a physics perspective to first order. Though things like slip and gear ratio limitations will impact actual results.

And I agree the "torque wins races" is a cliche born of ignorance.

Bottom line:

hp/weight is a very good indicator of acceleration. Without having a lot more info, it is the single best.

It is actual hp, not just "peak" hp that is important.

Thing is, people don't usually sit in the optimal gear. So, if you are sitting at 2000 rpm (or 3000 or pick your rpm) at 60 mph (or pick any other equal speed), the better accelerating car is the one with higher torque. That is since hp=torque*rpm and in this case rpm is the same (assumed same velocity). So, it is the same as saying the higher (instantaneous, not peak) hp car is the faster accelerating car.

So, a 240 hp 2900 lb S2000 gets mag accel results equivalent to a 250 hp 3000 lb, but torquier Boxster S, and a 280 hp, even torquier 3200 lb Z. Who could deny the results? Yet in the "real world" many think the S2000 is slower. Why? Because those many are thinking about real world non-max performance conditions. Where, yes, the torquier car is often at advantage.

So, I'll revise my position of months ago and say "it depends". Hp is what is ultimately the indicator. But in many real world situations (instantaneous, non-optimized) hp and thus perhaps torque, is relevant as well.

FCGuy

Oh, and it isn't simply a matter of "gearing". You can raise the gearing of any car. But you'll run out of revs. So, if you have higher revs, you can go to higher gearing, which gives more wheel torque. But higher rpm with the same torque means, yes, higher hp. So, it really is the hp afterall. Not just that the S2000 uses some magical gearing. It doesn't.

Zoran

[QUOTE]Originally posted by no really