Safe Speed Forums

This is really a poll for drivers of cars, not vans, motorcycles or any other vehicles, but all are welcome to comment, of course. I've set it to remain open 7 days.

I was looking at PeterE's thread about performance cars, which raises some interesting questions about what people drive, and how.

A year ago, I made the switch to diesel. My previous car was a Golf 2.8 V6 4Motion, and it was a dream of a car, with a very responsive engine. I was doing regular motorway journeys and my overall fuel consumption was about 27mpg. A change in circumstances has meant that I'm no longer doing the long motorway journeys on a daily basis, which cast doubts on whether I needed a car of such power as the V6 Golf. That, coupled with a trip to the other side of Reading and back in heavy traffic during which my fuel consumption averaged 19.8mpg started me thinking that it might be time to consider a diesel powered car.

I wanted to stick with VW Golf and wanted to have reasonable power for long journeys, so the obvious model to try was the 150bhp 1.9 GT/TDi. I was expecting to make some sacrifice in terms of performance, so took a test drive to see if it was acceptable.

I was amazed. At town speeds, the diesel car was probably better. On the motorway, acceleration to about 90 was effortless. One thing I noticed right away was the much taller gearing of the diesel. 2000rpm = 70mph in top. Both cars have 6 forward gears, but the V6 had a first gear which is way too low for a car of that power. It was too fussy, wanting to go into 5th at only 40mph, whereas the TDi felt comfortable at 50mph in 4th.

I put my order in upon returning to the showroom after the test drive. I wanted to know how this diesel car performed as well (even better in some circumstances) than the V6, in normal driving conditions. Well, on a test track with a guy sitting in the passenger seat with a stopwatch and the driver making 6200rpm clutch dump starts, the V6 does accelerate faster. But how many of us drive like that? The max power from the V6 was 204bhp @ 6200rpm. But at a more normal 3000-4000 rpm it wouldn't be developing 204bhp - probably quite a lot less. The GT/TDi is rated at only 150bhp @ 4000rpm. Anyone simply looking at these figures would dismiss the TDi as having only ¾ the power of the V6. But oh! - there's one thing that some people overlook as they ogle the max power figure: Max torque - as important as max power, if not more important, for practical purposes. The V6 max torque was 199ft. lb. @ 3200rpm. The GT/TDI figure is 236ft. lb. at 1900rpm!

So, on a race track the V6 wins. But for ordinary driving, that diesel power is right where you want it. No need for all that gear changing and revving. I can do almost everything with my GT/TDi that I could do with the V6. And the fuel consumption? I get nearly twice the mileage on the same volume of fuel. Normal average is about 47mpg, but with 50mpg or even 55mpg possible on journeys where speed is kept to less than 70mph.

The car I ended up with was one of the last MkIV models, which is what I wanted. I said I could do almost everything with this car that I could do with the V6. The V6 had a few nick-nacks that my current car does not have, but which I don't really miss. However! I really, really miss the 4 wheel drive of the V6.

There are good diesels, and there are grotty ones. I used to drive a TDS Astra, and tedious summed it up neatly. Hateful, hateful thing. Mind you, Vauxhall sort of prejudiced me against the thing by delivering it with a sticker marked "Quality Control Failure" attached to the inside of the front n/s door. And by one of the ventilation buttons falling off after a month. As for the engine, well, the company insisted on diesels for economy, but it was pretty mediocre. I used to average about 30mpg, though I did a lot of driving in London rush hour, which didn't help. Still, when you consider that I get 28 out of a 2.2 litre V-TEC now, that wasn't brilliant. As far as the actual driving goes, I'd rather have a variable valve timing than a turbo any day.

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Gatsobait - I agree some diesels are horrible. I drove a Peugeot 306 D rental car as recently as 1997, and hated it. It clearly had no turbo. But I have driven other, much better ones since. And I said in my original post, I was amazed by the Golf GT/TDi. Turbo+Diesel seems to be a marriage made in heaven!

There's a "fatal flaw" in this comparison. It's not torque at the flywheel that affects performance - it's torque at the wheels. Because diesels are lower revving they have much "taller" final drive ratios. The effect of the taller final drive ratio is to divide torque...

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I don't think I understand what's being said here. Surely the torque at the wheels concept applies to both engines in equal measure?

If you're alluding to the V6 4WD setup, you have a point. The V6 could accelerate out of bends and on any surface without breaking traction. The TDi can easily break traction doing that. Just last week, it broke traction on a straight road (damp surface) at only about 30mph in third. These are the reasons I miss the 4WD.

Next time, I was going to consider the Audi A3 Quatro, but a friend of mine has tried it, and didn't like the way it handled.

Quick example for the "direct drive" gear:

Diesel with 225 ft/lbs at the flywheel. Final drive ratio 2.5:1. Torque at wheels = 562.5 ft/lbs

Petrol with 175 ft/lbs at the flywheel. Final drive ratio 3.75:1. Torque at wheels = 656 ft/lbs

The point is that the difference in final drive ratios means that engine torque is not directly comparable. (Of course, the final drive is a torque multiplyer, not a torque divider, as I suggested earlier).

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

SS,

It's a deeper subject than I realised. I've just had a poke around a few websites, and came up with this. I think it explains my case better than I did. Of course, the acid test is to actually test drive the cars, and see how well each suits your driving style.

http://www.modernracer.com/tips/torquevspower.html



...and these days, I am indeed Mr. Average.

These comments on the concept of a "performance diesel" appeared earlier this year on http://www.austin-rover.co.uk:

"Perhaps I am old fashioned, but everyone I speak to who raved about their diesel engined cars tend to hurl superlatives at their cars' economy or cruising ability, then mention performance and driving pleasure second (if they mention that at all). And that's the thing. Yes, diesels are quick enough these days (a Golf GTi PD150 will pretty much stay with a ZS180), but they seem to lack that final finesse that marks out a "proper" performance car.

"Which is why I have a problem with the concept of a "performance diesel". Yes, they hurl you forward thanks to all that torque, but the whole concept of changing up at 4,500rpm - just when an engine should be getting interesting - is not really the trait of a performance car. There's also the on-off nature of the modern turbo diesel, which means that accelerating smartly from the lights involves dialling 2,000rpm and acting like a boy racer. If you try it with less, it tends to chug-chug-boost-accelerate-next-gear-please, which is not my idea of fun.

"Then there's the in-gear progress you get when accelerating from, say, 40mph in third: boost-boost-4,500rpm-another-gear-please-boost-boost-4,500rpm-another-gear-please. I am not saying it's not effective, but it's simply not that pleasurable. You will never wind-up a diesel simply for the pleasure of it, or enjoy the linear power delivery of an effective normally aspirated petrol engine. But you would drive one fast, and not really get the sensation of speed. Where's the fun in that?

"Don't get me wrong, I like diesels - I've driven a few I really like, such as the Rover 75 CDT, which in objective terms, is the best model in the range. And there is a sense that you're beating the system when you travel 600 miles between fill-ups. And you can go fast in the better examples of the breed. But so what? Follow a swiftly driven Golf TDi or BMW 330D and there's nothing more off-putting than seeing an ugly cloud of black soot coming out of the exhaust, as the car over-fuels yet again. So, diesels are worthy enough, and I admire those marketed for what they are: low-consumption cars. Those marketed as performance cars are where my objections lie: you can have a quick diesel, but don't kid yourself it's a performance car.

"It isn't one, and it never will be."

A few years ago I had a VW Group turbodiesel as a company car. It had extremely quick mid-range acceleration. But ultimately it was, to my mind, less enjoyable to drive than a petrol-engined car with less power and much less torque, but where you knew that there was a consistent relationship between pressing the pedal harder and going quicker, rather than having to constantly stay within a relatively narrow power band.

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

Paul's dead right about the "effective" torque thing - I was party to a rather protracted debate over this not long ago.

The relatively large torque figures of diesel engines are indeed generally cancelled out by the gearing. What tends to have everyone raving about performance diesels are two slightly more subtle issues:

One is the shape of the torque curve, with a performance diesel tending to have a much flatter curve than a peaky high performance petrol engine. Thus the diesel flatters someone with a "lazy" driving style, and minimises the loss of response when "caught with your pants down" in too high a gear!

The other is the related fact that the "geared up" diesel developing its power at 3500rpm tends to give us much more accessible power than the "equivalent" petrol developing the same (or more) power at 5500rpm. In normal driving situations we are much more likely to be near the optimum point on the diesel's power curve than we are with the more sportier petrol.

So the argument for diesels (apart from the economy) is that more power is available more of the time, whereas the petrol has more of a "Jekyll and Hyde" personality, depending on whether you choose to use the upper reaches of the rev range or not.

My current car is a BMW 330 (petrol), and I have to admit I thought long and hard about getting the equivalent diesel model. In the end I went for the petrol, as I'm pretty comfortable with the "Jekyll and Hyde" approach. Cruising around at 3000rpm it's smooth, quiet and steady, but use 5000rpm+ and it comes alive. The 330 diesel is great but I felt it was sat somewhere between two stools, neither as quiet and relaxed as the petrol running "off cam", nor as stirring when you wound it up. Having said that, I must confess I do sometimes wonder whether I'd rather be seeing 38mpg instead of the 28 that mine does!

Isn't it about now that it's traditional to have the debate about whether power or torque produces maximum acceleration?

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As a petrol head of long standing I could not live with a diesel. The second love of my life, after my wife, is my E36 1995 M3 and this is mainly due to the sound the engine makes as it runs through the rev range.

The M3 also develops a huge wave of torque (for a petrol engine) and will happily accelerate from 1300rpm in any gear. Mine spends about 70% of its time at low revs with excellent fuel economy and the rest of the time running through to as high as 7,500rpm. The aural symphony from the 3.0 litre straight 6 is just magical and it's something a diesel will never be able to compete with.

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Ross

Yes I'm a hoon, but only on the track!!!!

Interesting and valid points, guys who have posted since my last post. I admit, I loved the V6 "symphony", but these days I'm no longer doing the sort of journeys where I can appreciate it on a daily basis.

It has taken me a while to get used to the effortless nature of the diesel; Most driving is done in the 1700-2200rpm range, and there's no sensation of power delivery. It feels weird to change into top, see the revs drop to 2200, and know that you're already over the 70mph speed limit!

But I don't think "sound" is the mark of a performance car. Anyone who thinks that probably had some sort of 1980s "hot hatch" with one of those aftermarket exhaust systems with a 4" tail pipe. I saw one yesterday - a kid went blasting out of town making an unholy racket (probably impressed his passenger, and boosted his own ego as he levelled off at 40mph) but I'd like to bet my TDi could have run rings around that car.

As for diesels never being a performance car, it's worth remembering that even my lowly 1.9 TDi is only 6mph slower than that performance icon of the 1970s: the 4.2 litre E-Type Jaguar.

I will never, never, never, never ever own a diesel car...

Sorry all you diesel overs out there but I hat the fact that the petrol pumps and the diesel pumps are not together. Diesel pumps used seperate.

Every time I fill up I seem to be standing in a pool of diesel fuel that has been spilled before. Also the diesel is often splashed over the petrol pump as well so it gets all over my hands. So even though I don't own one my car still smells of it.....disgusting.

They still sound crap as well...

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Speed camera policy Kills

I have a question.

Do they do the Golf with VW/Audi's 1.8 turbo petrol?

Did you try that?

The low boost turbo petrol engines seem to offer a little of both worlds. Low down torque with a wide power band. Not quite the economy of diesel though.

Yep.its a great engine. The turbo is used in the GTI with the Seat Cupra getting the highest power version.

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Speed camera policy Kills