OT - 4x4 automatic car.

[Tim Streater]

And jet engines, too. There are largish models of B52 etc that uses jet engines. There's a UK co. that makes them, as well as others:

[Steve Firth]

[snip]

Yes, note carefully how it does not say anything about "better" or "better than you" perhaps your problems, and there seem to be many of them arise from your inability to read?

[Steve Firth]

Ok, but you'd also have to make a substantial cash refund in order for me to that piece of shit off your hands, about £400 is over-valuing any Freeloader.

[The Natural Philosopher]

we WERE talking IC pistons engines.

You can also get CO2 motors, rocket motors and rubber motors.

But whereas a fool might class them together in terms of basic operating principles, I would not.

[Tim Streater]

Now you're being soppy. You said, in effect: "Mine use electric motors, but others use something else." The something else includes jets as I expect you know.

[John Rumm]

I think that is what I was saying - as in all the graphs I have seen (and for that matter all the cars I have owned) the power peaks a bit before redline. It means you can usefully reach the peak without hitting the rev limiter.

(on my car IIRC its something around the 250 - 400 RPM below the 7500 limit. Given its got blowers, this is presumably set in the EMU parameter tables to make the engin more "drivable" and give a signal to the driver to change up before you hit the limiter)

[Roger Chapman]

Twin turbos rather restricts what that could be. I thought for a moment it might be a 3 litre BMW but that redlines at 7000 and in any case has it's peak power output a reasonable distance below the redline (5800).

[John Rumm]

Legacy GT-B 2.0 litre.

[Dave Baker]

You are absolutely correct in every respect. The curves you talk about are called "cascade curves" which plot engine bhp versus road speed in each gear. In the days before computers this is how optimum gear change points had to be calculated. You change gear where two adjacent curves cross each other which is where the bhp in the gear you are leaving has dropped (i.e. you MUST be past the peak bhp rpm point now) to the same figure as that available at the lower rpm which the engine will end up at in the next gear up.

The key point is you MUST rev ANY engine past the rpm at which peak power is produced to get the best acceleration. Terms such as "red line" which TNP keeps using are meaningless. Where the hell the tacho has its red line drawn has no bearing whatsoever on the engine's actual power curve or indeed the gear spacings.

For most engines with averagely spaced gear ratios you need to go about 500 rpm past the peak power rpm to get the best acceleration. It obviously depends on the exact shape of the power curve and the gear ratio spacings. The more gears you have, or the more closely spaced they are the less you have to go past peak bhp rpm. With an infinitely variable ratio gearbox the optimum strategy would be to have the engine at peak power rpm all the time.

[Dave Baker]

Don't be silly. As bhp = torque x rpm/5252 if an engine maintained the same torque at all rpms, or up to the "red line", the bhp would just keep climbing in proportion to rpm and it would never reach a peak power point and you'd never want to stop revving it. The torque HAS to drop below its own peak figure for an engine to reach peak bhp. Usually peak power is reached when the torque has fallen by between 7% and 15% from its own peak.

In fact mathematically peak power can be defined as the point at which torque is falling at the same incremental rate at which rpm is rising so the equation torque x rpm gives the same figure at two infinitely closely spaced points. Above peak power torque must be falling faster than rpm is rising and below peak power torque must either be still rising or falling at a slower incremental rate than rpm is rising.

[Dave Baker]

Nope, you don't usually go anywhere near the peak torque point if changing gear for optimum acceleration and the peak torque point is irrelevant anyway. All that matters is maximising power available at the wheels.

[Scott M]

Yes. Stall speed. Common term. The point at which the input side can't rev any higher with the output side locked.

[The Natural Philosopher]

Thats not a stall speed. The stall speed is the point below which the engine will cut out.

[Dave Plowman (News)]

Torque converter stall speed. You run the engine up to that against the brakes for the very best take off from rest.

It's a well enough known term. To those with any knowledge of autos.

[Huge]

Or indeed anything at all, given who you're "debating" this with.

[The Natural Philosopher]

From the opinionated dumpster.