You were supposed to imagine the transmission as a pulley

or a lever

or a hydraulic system


Here's an exercise:

Engine A makes 240 HP @ 9000 RPM. It makes a completely flat 140 lb-ft torque from 0 to 9000 RPM.

Engine B makes 240 HP @ 5000 RPM. It makes a completely flat 252 lb-ft torque from 0 to 5000 RPM.

Which engine is better? I could prove to you that A & B are exactly the same (ignoring NVH ).

 

Tho that's true, I think there's a more fundamental issue here. Just because you an spin the S2000 engine to 18,000 doesn't mean it will have the same torque at 18,000 as it did at 9,000.

 

I think we were talking about hypothetical situations. A given engine spinning twice as fast should be able to produce about twice the power. As someone indicated it boils down to the amount of gas burned / unit time.

I know the S engine is not capable of 18K rpm.

 

there are a ton of 99+ mustangs that have hit 13.8-13.9......food for thought

 

You're contradicting yourself. If an acceleration curve has the same shape as the torque curve than it is TORQUE that is determining acceleration! It's that simple.
You see it but you don't. It's right in front of you.

Then you go on to say that the proportionality changes with gear changes. NO IT DOESN'T, the magnitude of vertical scaling changes the proportionality (shape) is still identical. Did you even look at the graph closely? If you did you missed lots of information that is right in front of you.

The only reason scale is matched at all is because my graph is unitless. When your acceleration is measured in +-2 G and HP is 160 all of you acceleration curves would be invisible at the bottom of the graph. Scaling once matches the top peak of acceleration to the highest value in the graph. The following gears shrink from mechanical disadvantage and drag but they still have the same SHAPE.

It does in fact answer the original question of what determines acceleration. It proves it visually. What it doesn't do is tell you which is more useful which is still sort of a silly question. Both are only really useful with all the other variables.

-mikey

 

[quote name='neko_cat' date='Feb 3 2005, 05:20 PM']
You're contradicting yourself.

 

Wow. Grated, while neko's post doesn't address the question of whether weight along with peak torque or peak hp gives the best indication of a car's general acceleration, his post is spot on about the relationship between acceleration and torque.

You're BOTH correct. You two are just dicussing different topics. Neko about acceleration being proportional to torque, AlanP about power to weight ration giving the best estimation of a car's acceleration.

Why the hostility? It makes me sad.

 

[quote name='foolio' date='Feb 3 2005, 01:18 PM']
Engine A makes 240 HP @ 9000 RPM.

 

Nope, not correct.

You forget that while car A has 55% of the torque car B does, it can run 1.8 times shorter gearing and hit the exact same speeds in each gear. (1.8 * 0.55 = 1.0)

Therefore it will have the EXACT same torque to the wheels as car B, and will accelerate down the dragstrip at the EXACT same rate.

 

[quote name='Elistan' date='Feb 3 2005, 09:17 PM']