What controls your road speed is revs * overall gearing, and the diesel frequently matches or even betters (due to using the torque) the petrol in terms of when you can put your foot down and actually get acceleration.

And it delivers it's acceleration in one short burst and then you have to change gear. So the power delivery isn't especially progressive, and you have to spend more time changing gear than you would in a petrol...which was the point I was making.

Rob.

Of course the original post that sparked this thread was from a petrol fanboy - and now I've fallen into the trap of being a diesel fanboy. Doh!

and now I've fallen into the trap of being a diesel fanboy. Doh!

Your pipe, slippers, and string-backed driving gloves are in the post

Chris

A very interesting thread is this. And very emotive at that. At the end of the day Guys it's all down to what you want to have on your driveway. It does'nt really matter if your car runs on Chicken *hit as long as you are happy with it .

I also have both Diesel and Petrol Cars, and both are nice to drive .

No, let's not eh? That would be bad.

I take your point, although they're quite similar as a percentage 55-57%.

One ace that the diesel has up its sleeve - they are very difficult to stall. You can do hill starts with no throttle at all.

It's not much of an ace admittedly, but it can make driving in traffic a little easier.

the stalling thing depends on the diesel:D

And it delivers it's acceleration in one short burst and then you have to change gear. So the power delivery isn't especially progressive, and you have to spend more time changing gear than you would in a petrol...which was the point I was making.

Rob.

You really haven't got the hang of this gearing thing have you? A higher geared car can accelerate for longer in terms of road speed to get from one engine speed to another.

You really haven't got the hang of this gearing thing have you? A higher geared car can accelerate for longer in terms of road speed to get from one engine speed to another.

I'm confused - why is my diesel with a bigger percentage power band and longer gearing limited to 50mph in 3rd, whereas Nick's petrol with a smaller percentage power band and shorter gearing capable of 100mph in 3rd and hence pulls away from me quite significantly because he is capable of double the speed I am in that gear? As I see it both cars enter their respective power bands around 30mph... Or maybe I've missed the point?

Chris

Or maybe I've missed the point?

So have I... :confused:

Rob.

Higher gearing just moves the power band up and down the speed band. A higher gear doesn't make the power band any wider. Diesels may have higher gearing because they have more torque, that's all. It still runs out when the engine runs out of usable revs. Engine revs/Wheel revs is a fixed ratio determined by the gear.

I think what Ken is saying is that the narrowness of the diesel rev range/power band is mitigated (to a certain extent) by the longer gearing and torque at low revs - meaning you don't necessarily have to change gear to accelerate. I think.

That the petrol can do 100mph in 3rd is not down to long gears, but the high rev limit.

Prezactly.

Well, I actually think Nick's trying to judge both sides of the equation in a way that flatters petrol.

He's claiming that a powerful high revving engine is more flexible than a less powerful, higher geared, but lower revving one. Perhaps he should try and get 100mph in 3rd out of a petrol Octy with 100bhp or so (ideally 105 or 110) rather than 180, or try and see what the peak speed a BMW 325TD can do in 3rd.

Perhaps he should try and get 100mph in 3rd out of a petrol Octy with 100bhp or so (ideally 105 or 110)

It's possible.

Rob.

Surely logically, Diesel is the way to go.

Just to get back to another aspect - there is either 1/3 or 1/4 more calorific value in diesel (I forget) which, if it were not for taxation, is definitely the 'way to go' re world fuel usage.

More and more people are driving diesels now - it has taken a lot longer to catch on, unlike with the French whose government many years ago were lenient with taxation resulting in 1/3rd of the cars in France in the early 80s being diesel (and their energy requirements being less than ours).

Yep, and diesels can also run on chip fat I wonder what chip fat and Millers runs like?

Definitely - and a lot more fun to drive too. Just a shame they're not family friendly

Chris

Oh I wouldn't say that, we all fit in my other halves Aygo no problems.... When my daughter was first born we managed to get the 3 of us in to a Fiat Secento plus the buggy + weekend bags for trips to the lakes.... fun times

This is my third diesel car, and would not go back to a petrol, 1st was a pug 2lt hdi, 2nd a 110 octavia and last a 140 dsg octavia(wow) wot a diesel.

It's possible.

Rob.

If so, then it's farcically over-geared in 3rd, since it won't be capable of more than about 120 flat out.

If so, then it's farcically over-geared in 3rd, since it won't be capable of more than about 120 flat out.

Although its worth remembering alot of cars, especially less powerfull ones, make their top speed in 4th so maybe not that far off.

Surely the best thing to do is have a huge capacity petrol engine with lots of torque and long gearing. That way you can have the best of both worlds - something with a 5.7 V8 and 160mph top speed should fit the bill nicely.

Any idea where I could find such a vehicle?

You thought of sticking a big turbo on that thing Goochie?

Any idea where I could find such a vehicle?

You thought of sticking a big turbo on that thing Goochie?

a monaro super turbo :eek:

Well, I actually think Nick's trying to judge both sides of the equation in a way that flatters petrol.

He's claiming that a powerful high revving engine is more flexible than a less powerful, higher geared, but lower revving one. Perhaps he should try and get 100mph in 3rd out of a petrol Octy with 100bhp or so (ideally 105 or 110) rather than 180, or try and see what the peak speed a BMW 325TD can do in 3rd.

Where have I said I was comparing any particular engine with another?

Since you raise it, however, how about comparing Jason's TDi with my Octy then - 260 bhp diesel vs 180 petrol. His car won't do 100 in 3rd either.

Next!

My SE vrs is fast and performant enough for me. It's a great compromise btw economy and fun. I know a guy who owns a Subaru and he can't wait to change it for a performant diesel as he spends ridiculous amounts of money on petrol.

If I could afford a powerful turbocharged petrol car I would buy one.

I can't so I drive a diesel - end of.