Flat torque curves, good or bad?

[BALISTC]

My WRX has a fairly flat torque delivery....once it hits boost though

It has nothing til about 2800rpm then it JUMPS, makes max torque at 3600rpm and slightly tapers off towards redline, but otherwise pretty flat above 3600rpm...makes for a huge rush once it hits boost (I absolutely love the rush )

[Captiva Fan]

Originally posted by peter_vod69
You seem to have a bone for the M3 forg, can't say I blame you...

Sprung ... this is something I cannot help.
There are certainly others, but I know the M3's pretty flat. I suspect the majority of your supercars are pretty flat too, though.

But wouldn't a flat torque curve provide a lower power peak on the same engine than one that increased with RPMs in a linear fashion.

I suppose so, but then it comes down to what you can & want to achieve ... it's about control over the car, after all. Basically, there's not really a choice between a linear curve & a flat curve, the choice is more between a flat curve and something that looks like a cutaway profile of the Himalayas.

It seems to me that most power enhancements for naturally aspirated cars, without resorting to forced induction, usually involve more air/fuel, or more revs. From this couldn't it be said that the torque curve would change and become more "peaky" and to get more power out of an NA engine will inevitably result in a peakier torque curve?

Yes, but again it's just a case of "more is better"; some crappy mods lower the torque curve in some places, and it's those mods that make an annoying & dull car to drive on the road. Reasonable mods will beef up the torque curve in some places, but not lower it in others; really good mods should give nice flat areas if possible.

I remember a reviewer of the previous M3 saying the major difference between a big Aussie 6 and the M3's motor is the torque delivery, both have similar peak outputs, but the Aussie ones make theirs lower down, and are flatter, making them perhaps less driveable in wet conditions (the review was in wet conditions RX7 vs M3 vs WRX), while the M3 had a "linear torque delivery" which meant that it was a more exciting thing to drive in general.

They probably meant in comparison to the big Aussie 6's losing torque up the top end; when the E36 was around, we're talking the Ford 4.0 that doesn't rev particularly well as standard, and the GM3800 which is worse. The lack of top-end power indicates a dribbling-off of the torque curve; the M3 just keeps going 'til close to redline.

Of course, everything's a compromise ...

[Peter...]

No forg, actually it was mentioned because the test was done in wet conditions, and the torque delivery of an aussie 6 (particularly the ford ohc 6) would mean all that big ole' grunt arriving at once (= hairy moments!), whereas in the M3 the torque was not all there at once, rather it increased gradually in proportion to the revs, meaning it allowed for a more predictable drive in the wet.

The difference between a sudden shove and someone pushing you faster and faster I guess...

[Captiva Fan]

I suspect it's more like the M3's torque starts at 3000rpm & is prettty flat until 8000rpm, whereas a Falcodore starts at 1500 & is flattish to 5000 (if it's flat at all). Actually, I suspect that VN Commodores probably had beefy toque curves from 1000rpm 'til about 3000rpm ...

Put it this way, I wouldn't call turbo cars "boring", and modern turbo cars generally have a flat curve once they've achieved boost. It's a little harder in n/a cars, I imagine, as you don't have the option of boost control.

[gti6]

Originally posted by peter_vod69
GTi6 et al I know about the difference between various engines and their apparent characteristics, what I am still trying to find out is a definition of "flat" and "linear torque curves and someone to explain the difference to me.

My theory is that a flat torque curve is one that ramps up to, say 300NM at 2000rpm, and stays at or slightly above that for most of its rev range, whereas a "linear" torque curve is one that increases in similar increments throughout the rev range, IE 150NM at 2000RPM, 300NM at 4000rpm, 600NM at 8000rpm etc...

I think people are just confusing the two, hence flat=boring.

Correct?

I was just throwing in the engines for the sake of it.

A flat torque curve is wonderful to drive with, not boring at all. I bet well tuned V8 or V12 Ferrari has a nice flat torque curve. As a function of the torque and revs, power will be nice and linear as well. Not boring, fantastic and predictable to drive.

[gti6]

In fact, I'll go as far to say the further you move away from a flat torque curve, the more of a bitch the car will be to drive.

[IMOA]

Originally posted by peter_vod69
No forg, actually it was mentioned because the test was done in wet conditions, and the torque delivery of an aussie 6 (particularly the ford ohc 6) would mean all that big ole' grunt arriving at once (= hairy moments!), whereas in the M3 the torque was not all there at once, rather it increased gradually in proportion to the revs, meaning it allowed for a more predictable drive in the wet.

The difference between a sudden shove and someone pushing you faster and faster I guess...

You're still confusing torque and power peter.

A flat torque curve will result in a linear increase of power with revs. All these cars you think have flat torque curves actually fall away at high revs and the cars which you think have peaky torque curves are actually very flat

[gti6]

Exactomondo Greg!

[Peter...]

For want of diagrams, I don't think the term "flat" is correct though, surely linear is more accurate.

"BENN0 For flat and linear: Flat is a horizontal straight line. Linear is a straight line on any angle. "

Thats what I think too!

For example, a dyno torque graph like this / when compared to a graph like this -- then you would say the first is linear, and the second is flat, that is my understanding.

[coyote]

Porsche 996 Turbo



Power curve is linear, torque curve is flat.


Sweeeeeet!

[gti6]

Also Peter, just because the M3 may have a torque peak at over 5000rpm does not mean the torque curve is not tending towards flat.

My car's got a torque peak at 5600rpm, and well.. you've probably seen me ranting and raving about its flat torque curve.

[Peter...]

All it took was one post by coyote.

I think I had better wash my thinking cap... its all sweaty and yuck...

Whatever, I still think that VW golfs are boring! :D

BTW anyone got a dyno graph from an RX-7? Just for comparisons sake?

:worship: you guys, thank you for your explanations!

[Nick]

It's simple, since power is a derivative of torque x rpm then the flater the torque curve the more linear the power curve will be.

A torque curve that is linear (going up) would make the power curve more angled (faster rate of power climb). If your torque curve is headed down towards redline (what normaly happens in cars) then you need to look at bring up the torque high in the rev range to make more power. Rotaries seem to be good at this.

[coyote]

It's also worth noting that the graph above is for a Variocam engine.

According to a previous thread, it therefore has poor torque.

[Captiva Fan]

It may have poor torque, but it appears to have damn good drehmoment ...