cas2themoe

I have no idea why they rate the Torque with RPM. Maybe I'm just stupid but I've never had anyone explain this to me and I got confused on the RX8 vs R32 Thread.

I was looking at the rating of the VW R32 and has about the same HP as the RX8 but ofcourse the Torque is higher. Though the R32 Torque is higher its RPMS are not.

VW R32= 240HP @ 6200RPMS
236LBS @ 2800RMPS

MT RX8 = 238HP @ 9000RPMS
159LBS @ 5500RPMS

I did also notice that the R32 weight is about 400 LBS More!

We all know that RPMS for the HP does make a difference but what about the RPMS for the Torque? Do you all think it makes a difference?

nosubstitutec4s

well it does and it doesnt. the rx8 doesnt have a ton of low-end torque, therefore one would need to keep it in a higher rev range to get the full acceleration. This is a problem for the auto 8's, because the tranny wont shift to 1st above 30mph, leaving them at low rpm's in 2nd with very low torque. This is a trait of smaller engines, such as 4 bangers or the rotary.

the R32 has a 6, which has not only more torque, but it has it at a lower rpm. this of corse means that up in the higher rev range (which i believe is limited to 6700rpm, maybe alittle higher) could feel alittle bit weak.

Because i have personal experience with 6 cyl engines, one a porsche carrera engine and one a bmw 3- liter in a 5 series, i can tell you from personal experience that in the higher revs (around 6500+ for the porsche, 6000+ for the 530) the torque feels pretty weak when compared to the mid range of the engine.

take it for what its worth, but a higher torque at lower rpms is more livable for most people, but having the 9krpm redline is too much fun to give up, so ill learn to live with it *devil smilie*

AbusiveWombat

Knowing the peak torque, horsepower and the rpms that they are acheived gives you a better picture of what the power band is like. Obviously the best picture of the powerband is a dyno plot but those are not always available or as easy to publish as the peak values.

VW R32= 240HP @ 6200RPMS
236LBS @ 2800RMPS

MT RX8 = 238HP @ 9000RPMS
159LBS @ 5500RPMS

If we remember the equation for horsepower:
hp = tq * rpm / 5252

So @ 2800 rpms
the R32 has: 125hp

If we estimate that the RX8 has a perfectly flat torque curve it will have: 84 hp

It's horsepower that pushes you into the seat. So, in the lower rpms the R32 will feel much more powerful. The RX8 on the other hand needs to use it's gears to get acceleration.

The point at which the RX8 is making the 125hp is 4100 rpms.

Now, all this doesn't take into consideration that the RX8 probably has more aggressive gear ratios to take advantage of it's 9000 rpm redline. So, if both cars had identical peak horsepower values, perfectly flat torque curves, and had ideal gear ratios then both cars would accelerate at the same rate.

sti_eric

The "area under the curve" is more important than the actual peak torque number. The faster the torque comes on and the longer it stays high, the better. After 5252 RPMs, horsepower takes over.

Gord96BRG

You have to understand the difference between torque and power.

Torque is the twisting force that the engine can apply. An engine turning at zero rpm can have torque - in fact, for the most common type of electric motor, maximum torque is generated at zero rpm! Think of torquing lug nuts - you are generating torque on the wrench, but it's not turning when you get them tight, right? So - torque output is independent of rpm. For example, an engine can generate 100 ft-lbs of torque at 2000 rpm, and 150 ft-lbs of torque at 5000 rpm, whatever - the shape of the torque curve is a function of the engine's efficiency and tuning (and basic characteristics). There's nothing inherently more torquey about a 6 cylinder vs. a 8 cylinder vs. a 4 cylinder - it's all in the cylinder-specific design and tuning. That said, a diesel is torquier than a gas engine (more torque at lower rpms), and a rotary is less torquey than a piston engine.

So torque is a force. What's power? Power is the RATE of doing work. If you carry a heavy box for 100 yards, you have to apply a certain amount of force to move that box the distance. How quickly you apply that force is what gives you the power used - if you carry the box the 100 yards in 1 minute, and another guy carries the box 100 yards in 2 minutes, then you have both applied the same total force to move that box - but you used twice the power, because you did it twice as fast.

Related to HP in a car - one way to look at it is to say there's no such thing as power, there's only torque vs. rpm. This might sound crazy, but really, HP is ONLY a derived number! It is a fixed function based on torque vs rpm. A dynamometer, whether chassis (drive wheel) or flywheel, measures torque only, at varying rpms. When you get a dynojet printout, they've measured torque across the rev range, and then calculated the corresponding power. They never measure power! The formula for HP is HP = (Torque * RPM) / 5252 . That is why your HP value is always identical to your torque value at 5252 rpm - because that's how HP is calculated!

What some people consider a high torque engine is really just an engine that makes more torque at low rpm. What some people consider a low torque, high revving engine is only an engine with the torque curve shifted to peak at higher rpm. It's not low torque, just torque at higher rpm. That's also the secret to the resurgence of diesel engines in Europe - aside from lower fuel consumption, people have realized that big torque at lower rpm can be fun to drive too. If you have an engine that makes 200 lb ft of torque at 2000 rpm, or 200 lb ft of torque at 5000 rpm, what's the difference? They both make the same force to the wheels - yet the first engine makes 76 hp at the torque peak of 2000 rpm, and the second engine makes 190 hp at the torque peak of 5000 rpm.

The real key is the shape of the torque curve, and where the torque is produced. A high revving engine like the RX-8 simply has a torque curve that doesn't fall off as revs increase. The stereotypical American V8 has a torque curve that peaks low, but falls off over 5000 rpm (almost diesel-like), making it less revvy by nature. (That's just a function of tuning and design characteristics like overhead valve, 2 valves per cylinder, long stroke, etc - not the number of cylinders).

Remember - torque and power are absolutely fixed in relationship by RPMs. They are NOT independent numbers!

Regards,
Gordon

PoorCollegeKid

Look here for a fairly good explanation of torque, power, and how they make your car accelerate.

futureownr4sure

I beg to differ. This article sucks!

PoorCollegeKid

Care to elaborate? It points out the relationship between torque and horsepower in a fairly easy to understand way while still being technical enough to really make sense. I think it's one of the better articles written on the subject, which is why I posted it here.

BaronVonBigmeat

It's always annoying to hear someone say "well it makes good power but there's no torque" or conversely, "yeah it makes power but it runs out of steam at 5000 RPM's". Power is power, whether it's made with lots of torque or lots of RPM's. By definition, an engine with higher horsepower can do more work in a given amount of time than an engine with lower horsepower, regardless of what the torque or RPM's are. Or, it can do the same work but faster.

EDIT: And another thing. You'll often hear someone--maybe even someone who is damn good at turning wrenches--say "horsepower sells cars, but torque wins races". This is misleading. It's sort of like saying "Athletes sell endorsements, but legs win marathons." Yes, legs are technically what take you across the finish line, but strong athletic legs are only part of what makes a winner. I think maybe what they mean to say is, "peak horsepower looks good on paper, but the average horsepower ("area under the curve") wins races". Or something. Just because someone can turn wrenches well doesn't mean they are using engineering terms correctly. (And visa-versa, heh.)

To answer the original question in another way:

*Torque tells us how much twisting force we can apply;
* RPM's tell us how fast the twisting force is moving.

A dodge diesel makes, what...600 ft-lbs. of torque? But the winch bolted on the front bumper might make even more. Only problem is, it will turn veeery slowly...so you won't be replacing your diesel with a winch motor anytime soon. It doesn't make enough power. Unless you like to top out at 5mph. (Which is plenty fast when you're stuck in the mud of course.)