Help Me About Torque
 

I feel so stupid.. We just bought at RX-8 MT GT and I really want to know exactly what torque is. Can someone explain it to me in terms I will understand, as a pilot I thought I had an idea of what it was but I have a feeling I'm all wrong. Can you also compare what torque is to what horsepower is? People complain that the RX-8 has low torque, and I want to know exactly what they mean.

Torque is turning force - it has no 'time' element.

So its not a measure of work done, just turning force at a distance at that time.

Power - BHP - is force(torque) over time(RPM).

BHP is a mathermatical calculation based on torque - its not anything by itself.

Calc is:

BHP = (torque * RPM) / 5250

So BHP shoulr ALWAYS cross the torque curve at 5250 - EVERY time otherwise its a fake dyno chart.

But Torque at the engine is almost irrelavant as that is geared to the wheels.

Paul Yaw of Yaw Power wrote a very good description of Torque. It's a little long but very informative , a must read for any car enthusiast

Click Here for The Complete Text of Paul Yaw's excellent article Torque vs Horsepower

Thanks Rob... let me understand this completely....

From what I read the RX-8 has 159 ft-lb torque... is this correct?

so 159 * 5500 rpm = 874500/5250 = 166 hp?


I'm sure I must be missing something? I am just trying to get educated. The MT model advertises between 225-250 hp from different literature that i've read.. In order to get in that range my calculations show you must be at 7500 rpm to get 227 hp? Am I correct or am I missing something? Does the 6 speeds factor in somewhere? I don't know anything about gear ratio either, but I'm sure thats a different subject. Thanks for your help, I'll be looking for your reply.. Always, Erik

You are correct in your calculations. The rotary engine is good for high - revving applications. The RX8 gets its peak 238 horsepower at 8500 RPM. The only other car under $50,000, to my knowledge, that revs nearly as high is the Honda S2000.

The torque an engine produces varies over different RPM. So the peak torque, as you wrote, is 159 ft-lbs at 5500 RPM, so at 5500 RPM the vehicle is producing 166 horsepower.

If we take the original formula, horsepower = (torque * RPM)/5250 and swap it, we get torque = (5250 * horsepower)/RPM
So at 238 horsepower the RX8 has torque (5250 * 238)/8500 = 147 ft-lbs.

There are a lot of factors governing performance, and someone more knowledgable than I would probably better explain it.

If you use the search option, look for older threads in this category that Buger commented on. Forget the name, he knows his stuff and explains it well.

torque is most apparent at lower engine speeds. go drive a manual v8 - mustang, f-body, truck, etc. go WOT at 1500 rpm and compare that to WOT on the rx8 at 2500 rpm. you'll easily feel what torque is. i only picked 1500 and 2200 as ~ 1/4 their respective redline for a little more equal comparison.

what you'll feel is low rpm horsepower, which becuase of the low speed of the engine, the torque per turn of the motor must be huge to make a decent amount of horsepower at that low engine speed.

it's the displacement and force per turn that large motors make (not to mention the low-speed bias in the tune of most american sports cars, and all trucks in general) which generates that really powerful off-idle pull.