torqe /power

Yes

So one revs higher than the other

I've not seen an SLK with a focus diesel engine in it, but I'm prepared to bet the cost of doing it & the depreciation would far outweigh the fuel costs.

BHP is the product of torque and engine speed. If you could keep the max torque figure constant, the higher the engine can rev, the higher the BHP. And petrol engines can usually rev higher than diesels.

But the maximum torque usually follows a sort of curve with the maximum being at somewhat lower revs than the max BHP.

and a tractor engine might have far more torque than either and far less BHP, it doesn't matter a lot, you buy the vehicle that you need, want or choose.

It's not that simple. Diesel has a higher thermal efficiency than petrol and burns at a different speed. It's all a bit complicated when you really get into it, especially as you're comparing apples to oranges to begin with.

"Mrcheerful" gurgled happily, sounding much like they were saying:

I'm quite surprised Merc don't seem to do a diesel SLK - not even in very diesel-friendly countries like France, although they do get a diesel CLK cabrio we don't.

Audi's diesel A4 convertible and BMW's 3-series diesel convertibles seem to be selling well enough here.

It's the peak torque figure, yes.

But the SLK will produce something like 90% of that 229 lb ft between

For me, yes, every time. I love big torquey engines but don't like most diesel engines power / torque delivery characteristics.

I still think they should put another £1 a litre on diesel.

Oi!!!!

In article , Pete M says... The Focus will produce its 184 lb ft between

Why not? The gearing is done to take this into account.

Changing gear's too difficult for him.

Yes. POWER is king, smokers lose every time.

SLK 0-100 Km/h 6.9sec (1405Kg) Focus 1.8 TDCi 0-100 Km/h 10.8sec (1374kg)

Anything over 7.5sec is sadly inadequate.

Oi! I'll have you know I'm rather good at changing gear, it's just that I don't like cars that you have to row along with the gearlever, and there are a whole load of diesel powered cars that while having large amounts of torque, can only produce said torque over a very narrow rev range and only manage to do that if the turbo is spinning merrily away. When they're off boost, they're hopeless. The trend for more powerful diesels just means that they tend to whack the boost up more and more.

Drive something properly torquey with a petrol engine and you'll know why I don't like diesels. An MG ZT 260 has torque on tap no matter which gear or how many RPM you're using, the headline torque figure may not me as impressive as that of a V6 Merc CDI but the MG is the more torquey car to drive - because the torque is always there, you don't have to wait for a turbo or to get into an optimum rev band.

Gearing can only hide so much, long gearing makes a lot of new diesels good on the motorway because 75 mph cruising speed tends to be in the optimum rev band. Away from motorways and A roads they tend to be very peaky and irritating to drive compared to a good petrol engined car.

That's what I thought, until I realised that, instead of keeping the engine spinning from 4-7k rpm, you get the same performance in a diesel from 1-4k rpm.

I hated my Passat TDI when I first got it, but that was because I was trying to drive it like I would a petrol engined car.

Indeed, but it's nicer to have poke from 1000 revs right through than from 1500-4000.

To be honest a lot of the engines I love don't rev to big numbers. The MG ZT V8 runs out of poke at about 6000 rpm and changing gear at 4500 isn't much less effective than redlining one, but it's the whole delivery issue again. In the MG the poke is always there and you change gear because you want to - NOT because you have to. 3rd gear in one will happily do all your needs from 0-90 mph.

Yeah, it took me a while to realise this too, but once you know you can leave it in third and still pull away at 20mph without it bothering the engine, then it all becomes easier. My old VW LT35 diesel van without a turbo runs in third most of the time around town. Loaded or empty it just chugs on like a traction engine with no noticable change for weight on board. Needs 2nd just to get it moving from stationary, but then its 3rd all the time. 1st is a crawler gear on this van though. Sometimes I get in it after driving a petrol for a few days and have to tell myself not to bother changing down all the time like I have to do in a petrol.

Mark

Christ, there speaks a man with a small togger ;-) Mark

Well if you drive the RIGHT [1] petrol engines you just plain don't. Normalised engine performance.

As for spark ignition fuel costs due to higher consumption there's always LPG in UK and E85 in other countries (Ireland/Sweden I believe).

What does that actually prove?

All I can see is a comparison between 'cooking model' diesels and high performance petrols.

How does the graph look if you compare, for example, a VAG 2.0FSI vs a VAG 2.0TDI? - they're largely comparable engines in the range - both in the region of 150bhp and pretty close on price.

I know there's the 'but the diesel has a turbo' argument, but that's a moot point as just about every diesel on the market has a turbo, whereas petrol turbos are more limited in their applications and are usually reserved for higher end performance models.

Gearing is a big part of the comparison on the road - diesel boxes are designed to gain comparable speeds to petrols over a smaller rev. range, so the diesel will gather speed just as quickly as the petrol, but gather less of a gain in revs. for a comparable gain in speed.

I need more changes of gear in my N/A 150bhp petrol to perform overtakes than I did in my 2.0TDI with 140bhp.

Nah, he just thinks the Nissan 200SX is the bestest car in the whole world, ever.

Surely it's not as simple as comparing bhp? Sounds like comparing apples and pears to me. Wouldn't the only true comparison would be the torque produced at a certain rpm?