Diesel vs Petrol

tomstickland

Turbo Diesels tend to generate large torque figures. This won't make them any faster than a properly driven petrol car with the same sort of power output, but it can be more useful for most people. They certainly aren't sluggish though, unless they're some sort of dismal spi low boost economy engine.

I used to have a revvy petrol engine and you had to be wringing it's neck between 4000 and 6500rpm to make proper progress. Most people don't drive like that.

sebdangerfield

I've said on here for ages now that Petrols are a waste of time. Since Robert Huber invented torques petrols have been a close second behind the mighty diesel.

I was so convinced by the argument in the last d vs p thread that the diesel TT was a perormance car I sold my Petrol V6 twin turbo 2.5 Mondeo and am looking for a diesel to replace it. The drop from 400 bhp to 170 doesn't matter, the majical torque will make it just as fast.

This has been done to death guys, it just ends up getting nasty and upsetting people who genuinely believe their hard earned has been spent on a supercar that does 50mpg.

motorguy

sebdangerfield wrote: »

I

This has been done to death guys, it just ends up getting nasty and upsetting people who genuinely believe their hard earned has been spent on a supercar that does 50mpg.

Moreoften its the people who think their petrol car is 'the answer' who get upset when its pointed out how good diesels are.

sdavi3680

I was just comparing the fuel and road tax costs for the Polo 1.4 SE and Polo 1.6TDI SE. There is £845 difference between the list prices. But then using the website below as a guide, you would save £2050 over 5 years (which would probably be the minimum we would keep the car for) based on 12,000miles and road tax.

http://www.carpages.co.uk/guide/volkswagen/volkswagen-polo-se-1.4-5dr.asp
http://www.carpages.co.uk/guide/volkswagen/volkswagen-polo-se-tdi-1.6-%2875ps%29-5dr.asp

sebdangerfield

pgilc1 wrote: »

Moreoften its the people who think their petrol car is 'the answer' who get upset when its pointed out how good diesels are.

Hmmmm, define "good". I've said on other threads how good my diesel was. Depends on if the question is "does it go fast Mr?" too I guess.

On the other thread (one of many now) the main argument about what was good was one person saying a Diesel TT with a 0-60 time of 7 and a bit seconds was a performance car. "Good" "Performance" and "0-60 in 7.5 secs" wouldn't crop up in many sentences my car nut friends would say. This proves the matter is subjective and as a result, each person chooses the car on it's individual merits and their own needs. Someone wanting real performence would scoff at those figures but someone not so into cars would be more than satisfied.

My main gripe with threads like this are the comparisons. A diesel with a turbo to a petrol without one is not a comparison. Both engines have hugely different characteristics. Most of the benefits people say of diesels are apparent in the forced induction petrols bar the fuel economy which brings it back to "they're cheaper" rather than "they're better".

A better comparison is a turbocharged diesel and a turbocharged petrol. The diesel still has more torque but the gulf's much smaller and the torque is available at lower revs in the diesel. This isn't good for performance contrary to what people commonly believe. It's good for easy driving. The much hyped revisions to the Audi V8 LM engine were nothing more than the ability to raise the rev limit meaning less gearchanges in short corcorners and raising the peak torque higher up the rev range giving that boost when it was needed for performance when exiting high speed corners. It's lower in road car diesels to save fuel and make the car easier to drive in town. Both characteristics of economy over performance.
The petrol turbo will have a much smoother torque curve giving better response and the fact that that torque is all the way accross the range means it won't run out of puff as quickly, the main gripe of diesel owners.

tomstickland

Very roughly, peak power to weight ratio will give a very strong indication of the outright performance ability of a vehicle in terms of acceleration.

The extra low torque of a Diesel engine is handy for every day driving but it won't make the car a rocket.

The performance figures for my 1.9 TDi are slightly worse than those for the 1.8 16v petrol engine that was produced at the same time.

I think that turbo Diesels make a very good case for a car, considering that you can have decent performance and still manage 45mpg or whatever. They respond a lot better to a bit more care with driving style too. This is on account of their higher compression ratio, the lack of throttle and that they can run very lean, unlike petrol engines.

a Diesel TT with a 0-60 time of 7 and a bit seconds was a performance car. "Good" "Performance" and "0-60 in 7.5 secs" wouldn't crop up in many sentences my car nut friends would say. This proves the matter is subjective and as a result, each person chooses the car on it's individual merits and their own needs. Someone wanting real performence would scoff at those figures but someone not so into cars would be satisfied.

It's not bad though. Anything below 8s is doing quite well for itself and definitely more performance than economy.

I've had a few side-by-side comparisons over the years and sometimes it's amazing how little difference a significant amount of power can make. I had a slighly modified 2.0 8v hot hatch (145BHP at the time) and a friend in a Porchse Boxster could not pull any distance on me down some flowing roads.

titanflux

I've had diesels exclusively for 10 years. I last has an Audi A6 3.0 TDI V6 with an auto box. I now have a naturally aspirated (non-turbocharged) BMW 3.0 striaight-six petrol auto and they are nearly the same on paper in both bhp and max Nm torque. (I know, auto's are for old people - I am 36 and fail to see the point of a manual in this day and age - I can always use my flappy-paddles, but why bother when I can just switch on sport mode?)

However, the petrol (esp after all those diesel years) is so much smoother to drive, easier to control and predict, no turbo lag of course, and about 5mpg better fuel economy. Oh and it does 0-60 in 6.6 secs - about a second better than the diesel. Also less car tax as it's about 40g/km less CO2 emissions. It's been a breath of fresh, non-turbocharged air! It's just a pity petrol fuel isn't still 10-15p per litre cheaper than diesel like it was a year ago, but I'm still saving, esxpecially as picking up a big petrol is a bargain compared to the cost of an equivalent diesel - you'd have to do many, many tens of thousands of miles before you'd recoup the extra cost of the deisel car.

alo6

i have a golf turbo diesel and i would never go back to petrol.

The lag isnt bad, not really alarming.
Certainly shifts.
Got from Glasgow to Portsmouth (450 miles) in under 3/4 tank.

sebdangerfield

tomstickland wrote: »

It's not bad though. Anything below 8s is doing quite well for itself and definitely more performance than economy.

QUOTE]

Totally disagree. If the diesel Audi TT is more performance than economy why is there a faster, more powerful 2.0l petrol?! The whole reason of the diesel tt is cheaper tax, cheaper bik and more mpg at the sacrifice of a second and a bit of acceleration.

motorguy

sebdangerfield wrote: »

I've said on here for ages now that Petrols are a waste of time. Since Robert Huber invented torques petrols have been a close second behind the mighty diesel.

I was so convinced by the argument in the last d vs p thread that the diesel TT was a perormance car I sold my Petrol V6 twin turbo 2.5 Mondeo and am looking for a diesel to replace it. The drop from 400 bhp to 170 doesn't matter, the majical torque will make it just as fast.

But you're not comparing like with like though. The average mondeo buyer have the choice between the 2.0TDI and the 2.0i petrol version.

The diesel variant will be more driveable, offer better economy, and have a better residual value - and to get that they lose out slightly in the 0-60 traffic light grand prix to the petrol version. I think most people look at that and its a no brainer for the diesel.