Is torque really relevant?

[otolith]

I'm wary of those graphs (on Rob's link), I think they are approximations based on published power and torque peaks, though obviously they are right for the manufacturer provided data points. But what you have got is torque falling from 413lbft to 335lbft over the 1000rpm range that your gearbox is trying to keep the engine in.

[RobM77]

ddom said:

RobM77 said:

Nope, the torque curve from my engine is completely flat between the revs I mentioned:

Seems to make sense from this graph?

There's still no "steep rise" between the 2000 and 3000rpm we were talking about.

[Fastdruid]

RobM77 said:

otolith said:

RobM77 said:

I'm convinced my car's ZF8 box isn't configured to work with the car's engine properly. Apparently my car has 560Nm of torque between 1500rpm and just over 3000rpm. If I push the throttle down in drive, after a second of faffing about with gears, the gearbox selects a gear that delivers about 3000rpm, right at the top of the engine's torque peak. It then shuffles through gears frantically as I accelerate, keeping things between 3k and 4k. Maybe I'm wrong, but I'm sure the car accelerates best between about 1600 and 3000, plus that involves no gearchanges and results in a doubling of my road speed, which is enough for most overtakes. One day I'll time it on a TED test to find out.

Peak power is 4000rpm. In one gear it will accelerate best between 1500-3000rpm, but maximum acceleration at any given road speed will be in the gear that gets you closest to 4000rpm. I think you are just feeling the typical anticlimactic diesel power delivery, along with an artificially managed torque plateau.

Interesting, thanks. Yes, the gearbox centres the engine around peak power, but it feels subjectively slower than from 2k to 3k.

That's because torque is dropping off but at a slow enough rate that power is still rising.

Personally I dislike revving a car into this zone. It feels "off", it's in part why despite mine revving to 6.5k+ (I'm not entirely sure where the limiter is) I don't generally take it up past 5k, because that's where the torque drops off. This is in part why despite the vehement arguments that diesels make power past ~3k I *know* that they're not lying but they're not being totally honest either and I'd dislike it anyway...

[Fastdruid]

ddom said:

RobM77 said:

Interesting, thanks. Yes, the gearbox centres the engine around peak power, but it feels subjectively slower than from 2k to 3k.

Isn't that also due to how acceleration feels from low speed. In the case of a modern FI diesel the torque curve is short and steep.

In part, yes. People don't feel *constant* acceleration, they feel the change in rate of acceleration. Hence cars like the RX-8 with it's very flat curve "feel" slow and diesels with their very steep increase in torque at the start of the curve feel very fast. Even when they're not. Same actually with laggy petrol turbo cars, it's that build of power as torque increases and increases again that makes it feel fast. With a diesel particularly as you have a very short rev range you then have to go for the next gear quickly and you experience that rise in torque (and hence acceleration) again.

As a mildly amusing anecdote, had a Galaxy TDCI140 for a couple of weeks, my children thought it was massively faster than the Mondeo....It's not, it is ~3 seconds slower to 60 but the way it made its power made them think it. Equally the Mazda 6 MPS we had, the mildly laggy turbo made it feel massively fast. It's quick, but actually it's not that much quicker (apart from off the line) than the Mondeo. Yet it feels as if it's massively, massively faster.

[Equus]

Fastdruid said:

People don't feel *constant* acceleration, they feel the change in rate of acceleration.

[otolith]

Turns out that people don't mind feeling a jerk...

[Alex_225]

In response to the thread title, I've just had my S Class re-mapped and it now has around 470lbs-ft of torque so it feels very relevant right now.

Not insane horsepower but the extra torque means in gear it moves pretty well!

[s m]

otolith said:

Turns out that people don't mind feeling a jerk...

In the era of the turbo diesel, torque is cheap.....

[robinessex]

Acceleration requires a force. Torque is a force. More Torque, the better. That's Torque AT THE REAR WHEELS. You have a gearbox between the engine and wheels to multiply the engine torque.

[RobM77]

Equus said:

Fastdruid said:

People don't feel *constant* acceleration, they feel the change in rate of acceleration.

We do feel acceleration, after all F = ma and we feel force on our bodies. I can feel gravity pushing me onto my chair now, and the equivalence principle states that this feeling is indistinguishable from the sensation of acceleration. However, it sounds plausible that we feel rate of change of acceleration more, after all we get accustomed to feeling the steady force of gravity our whole lives.

[Gary C]

RobM77 said:

Sorry, by the top of the pedal I mean the first portion of pedal movement, so from 0% to n%. If you start at n%, there is no lag. A typical movement after turn-in when you transition from brake to throttle might be going gently from 0% to 10% and then gradually working down to a steady throttle to balance the car, which would typically be about 10-20%. As described above, in a modern petrol car nothing happens when you do this, and then you suddenly get this jerk as the ECU gives you whatever throttle you've asked for.

Ah, get what you mean and agree with you.

Thankfully my 911 has a butterfly and good old 8 bit Motronic

[ddom]

RobM77 said:

We do feel acceleration, after all F = ma and we feel force on our bodies. I can feel gravity pushing me onto my chair now, and the equivalence principle states that this feeling is indistinguishable from the sensation of acceleration. However, it sounds plausible that we feel rate of change of acceleration more, after all we get accustomed to feeling the steady force of gravity our whole lives.

Yes. We can feel acceleration (force) but not velocity.

[Equus]

RobM77 said:

We do feel acceleration, after all F = ma and we feel force on our bodies. I can feel gravity pushing me onto my chair now, and the equivalence principle states that this feeling is indistinguishable from the sensation of acceleration. However, it sounds plausible that we feel rate of change of acceleration more, after all we get accustomed to feeling the steady force of gravity our whole lives.

I wrote a paper on human perception of car handling, a few years ago (...as you do).

Certainly we do feel the force of acceleration on our bodies. You only have to go swimming for an hour, then feel gravity re-asserting itself as you climb out of the pool for a demonstration of how that feels.

But by far the more sensitive element of how we judge acceleration is via our sense of balance, detected by hairlike sensors picking up the movement of the fluid in our inner ear canals.

Under steady-state acceleration, that fluid is displaced in a certain direction, which we can sense, but then stays displaced until there is a change in the rate of acceleration.

Hence we are far more finely attuned to detecting the rate of change of acceleration (when the fluid is actually moving) than steady state acceleration (when it isn't).

The inner ear is also responsible for sensing a lot of what wannabe driving gods think is their perception of the difference between understeer and oversteer in FWD and RWD cars. In fact it's usually understeer in both cases, and most of what they're actually feeling is the suspension diagonally pitching in different directions (FWD cars are designed to lean on the outside front corner, RWD on the outside back corner, to keep the driven wheels loaded).

But we digress...

[RobM77]

ddom said:

RobM77 said:

We do feel acceleration, after all F = ma and we feel force on our bodies. I can feel gravity pushing me onto my chair now, and the equivalence principle states that this feeling is indistinguishable from the sensation of acceleration. However, it sounds plausible that we feel rate of change of acceleration more, after all we get accustomed to feeling the steady force of gravity our whole lives.

Yes. We can feel acceleration (force) but not velocity.

Obviously not, no. Has anyone mentioned that?!

[LimSlip]

Equus said:

Hence we are far more finely attuned to detecting the rate of change of acceleration (when the fluid is actually moving) than steady state acceleration (when it isn't).

Jerk.

[Hungrymc]

Equus said:

Hungrymc said:

Struggling to see the parallel to the caterham.

That's because it's a contrast, not a parallel.

Haha... good point.

Anyway, I think a close ratio box complements a more peaky engine. Less so something with a significant and broad torque curve (it may still help with ultimate performance and efficiency, but my view is it masks the character of the motor)