Slightly OT: Petrol or Diesel?

[bert]

In message , "Dave Plowman (News)" writes

Petrol engine power curve drops off at higher revs.

Yup the way to drive a diesel is as hard as possible.

[bert]

In message , Tim Lamb writes

Could well be. There was a joint Ford/Peugeot diesel - I have one in my motorhome and I'm quite happy with it. I have a Trannie Puma engine in my Land Rover and that's Ok - bloody awful 6 speed gearbox though.

[Clive George]

Answers own question : 5K RPM or so, ie not dramatically different from the road ones.

[John Williamson]

The fastest diesel I've used turned at over 20,000 rpm, but that was on the front of a model aeroplane, and used a mix of ether amd nitromethane as a fuel.

The ones in the JCB world speed record car are limited to 3800 rpm, which is slightly slower than the redline in our company Focus.

[Adrian]

Several, actually, including the 2.7/3.0 v6 used by Jag & LR.

[Clive George]

And is a two-stroke running on a completely different principle to the ones in cars :-)

[John Williamson]

A minor detail... It's the same as some large ship diesels, but without the turbo and fuel injection. ;-)

[Dave Plowman (News)]

So that would be the same as a petrol engine running on hydrogen? ;-)

[Clive George]

Large ship diesels are another cycle again. They rely on blowers, and have valves. The model engine two stroke is the same as a motorbike or lawnmower engine, only without a spark. It's knocking all the time :-)

[The Natural Philosopher]

you haven't run a performance petrol engine with a rev limiter then?

[The Natural Philosopher]

4500 max.

To get the compression ratios with anything like a reliable combustion chamber left you need a long stroke small bore engine. That makes them unable to rev as well as the short stroke petrol screamers.

[John Williamson]

Compression ratio's a touch higher.

[The Natural Philosopher]

Rubbish. Te way to drive it is in the mid range of RPM., unlike a tuned petrol where to get the max you actually have to rev the guts out of it.

[The Natural Philosopher]

No nitro in diesels usually. ether, parafin and amyl nitrate IIRC.

nitromethane was in the glow engines - still is.

The le mans winning audis are reputedly redlined at 4500-5000.

[The Natural Philosopher]

not totally. Its still a compression ignition engine..

[Mike Barnes]

"Dave Plowman (News)" :

I don't think I put it very well. Diesel drivers like the ability to accelerate briskly when the engine's at cruising speed, and this is often the reason for preferring the driving experience of diesel over petrol. It's often misleadingly referred to as "torque" and is viewed as more important than power for acceleration. In fact, power is what matters for acceleration, but with a petrol engine at cruising speed you have to change down to access that power.

So if diesel's "brick wall" effect causes you to plump for an auto box, you might just as well get a petrol engine with more power.

That's leaving aside, for the time being, economy.

[Dave Plowman (News)]

Not one where the limiter cuts in at or near peak torque, no.

[Dave Plowman (News)]

Would you care to explain the difference between torque and 'power'?

There's little difference these days when both are driven hard. Diesels get more economical pro rata at light 'throttle'.

[bert]

In message , "Dave Plowman (News)" writes

That's because peak torque is about mid-range on a petrol engine, about

3000 - 3500 on a standard production car.

[bert]

Bollocks Keep your right foot hard in on a diesel and use the gear box.