Since this is my first diesel car I want to know: At what RPMs should I be shifting in normal driving? In sporty driving? To maximize performance? To maximize MPG?

Thanks,

You need to be doing what is best described as 'surfing the torque'

How to drive depends on the car but you soon get the feel for how to drive it best. Accelerating slowly does not give best MPG as the turbo is not providing the extra air needed.

Try driving so the change puts the engine revs *back* at about 2,100 to 2,200Revs,
in the higher gear you have just changed into.
In effect this means you are changing up at about 2,600 ( ish)
Theres no point at all going over 3,000 revs as max torque is under 2,000
`Sporty` driving in a diesel means staying in the max torque range, some people just don`t get this and start revving Diesels over 4,000 revs where the torque is actually less.
( these are not exact figures but, typical)
In other words Sporty driving with a diesel is available without effort as you don`t have to rev it.
Economy driving on a long run means keeping the speed down as on any car, also if you use the power available all the time to `surge` forward in normal driving its going to use more fuel.
Its easy to start doing this too as the torque is right there, at low engine speeds.
Regards Mike

Not all diesels drive the same.

Bunny's Bravo is very revvy and gives awesome performance if you let it get up to 4000rpm before burying it into the next gear. The marea is different, certainly a lot more torque rather than bhp.

From what I can gather (not being a physics expert) in theory power is torque x rpm. However, in reality, the engine loses efficiency as the rpm increases and so the torque cannot be maintained at high revs. This doesn't mean that less bhp is generated, as the increase in revs compensates for this.

According to Fiat specs, the GP multijet 130 engine develops maximum (130) bhp at 4000rpm - well past peak torque. It's therefore at 4000rpm speed that you should reach the peak of acceleration. However, it will generate enough bhp at much lower revs than you'd expect from a typical petrol car and so you can get very good acceleration whilst changing gear at around 2000.

...Or have I got completely the wrong end of the stick?

tomgp said:

From what I can gather (not being a physics expert) in theory power is torque x rpm. However, in reality, the engine loses efficiency as the rpm increases and so the torque cannot be maintained at high revs. This doesn't mean that less bhp is generated, as the increase in revs compensates for this.

According to Fiat specs, the GP multijet 130 engine develops maximum (130) bhp at 4000rpm - well past peak torque. It's therefore at 4000rpm speed that you should reach the peak of acceleration. However, it will generate enough bhp at much lower revs than you'd expect from a typical petrol car and so you can get very good acceleration whilst changing gear at around 2000.

...Or have I got completely the wrong end of the stick?

Click to expand...

Let me show you the other end eh?

My GP 1.9 JTD Sporting is also my first diesel - I was asking the same sort of questions a few months ago.

In short, I tried to "surf the torque" and while it certainly makes for quick driving, I find that revving to 4,000rpm gets me the best acceleration.

Yep - that's my experience too - As backed up physics experts. I looked into it as what the man on the street was telling me didn't seem to make a lot of sense.

Hellcat said:

Let me show you the other end eh?

Click to expand...

Be my guest

Is bhp meaningless when you have lots of torque?

I think if a car really is not giving you more power when you are beyond peak torque then it is an inefficient engine that loses torque rapidly as the revs increase. The GP 130 sporting engine is able to maintain reasonable torque and hence achieve significantly higher bhp at 4000 revs than at 2000 where it has peak torque.

This article explains it pretty well:-

Power and Torque Explained

More torque at lower revs also means more power at lower revs, so even though your torque starts to drop off after 2000RPM the higher revs make up for that. A result of the torque curve being

Power is the result of torque and RPMs combined, so they're all related. In other words you will get maximum acceleration up to your peak power output.

I find surfing between max torque and max power gives max acceleration.

Not sure I can give a mathematical reason for it, but in experience (have had turbo diesels for 4 years) this gives the best performance.

tomgp said:

Be my guest

Is bhp meaningless when you have lots of torque?

I think if a car really is not giving you more power when you are beyond peak torque then it is an inefficient engine that loses torque rapidly as the revs increase. The GP 130 sporting engine is able to maintain reasonable torque and hence achieve significantly higher bhp at 4000 revs than at 2000 where it has peak torque.

This article explains it pretty well:-

Power and Torque Explained

Click to expand...

Thanks Tomgp, great article. So from now on I'll be shifting a 4,000 when "racing" at the stoplight. . . . always respecting the published speed limits . . .

Great article. And the reference to a 'modern turbodiesel car' with 130bhp at 4000rpm somehow reminds me of something...