RE: RE: VVL anyone?
Slim said:
Also, the golf TDI on the track did race a civic Type R, not Si.
Where? When? Which cars? How badly was it beaten? People argue over this race a lot in forums and newsgroups but I have not seen any evidence of the actual race occuring. There is so much "I heard from a friend..." information about cars flying about on the internet, and you've got to sort the wheat from the chaff.
Slim said:
porcshe GT3's massive 28 lb/ft @5000?? thats crap. I'd sooner take 244 @1900 anyday.
It's 280ftlb @ 5000rpm. It isn't crap - it's about average for a highly tuned road engine (between 75ftlbs/litre and 80ftlbs/litre for something that is very driveable). I'll admit that the
power/torque of thePorsche 911 GT3 shows that is has lower torque at lower RPM, but so do all engines for cars designed for going fast. It's better to have it like this than have a flat torque curve with lower torque - if you want to win races.
I think you are missing the major difference between diesels and high revving powerful petrol engines. It's gearing. Look at these two simplified examples:
- Diesel - 197ftlb of torque between 1200 and 4800rpm, where the torque vanishes. That gives a peak power of 180BHP.
- Petrol - 115ftlb of torque between 1200 and 8200rpm, where the torque vanishes. Again, peak power of 180BHP.
Ok, not ideal - the redline is where peak power occurs. But the torque figures are about right if you average across the RPM range.
Imagine you had both engines connected directly to the wheels of a car. The diesel produces more torque, so it will accelerate faster. However, it will also hit the redline sooner, and stop accelerating. The petrol engine can keep on accelerating, albeit with a lower torque.
So now, let's gear the petrol engine so that it produces the same amount of torque at the wheels as the diesel. That means the torque is multiplied by 1.71, and the RPM divided by 1.71. Now let's look at the numbers - the petrol engine is producing 195ftlb of torque, and the maximum output RPM is 4800. Hang on, isn't that exactly the same as the diesel engine?
That's why producing torque at high RPM (power) is an advantage - it allows you to take advantage of gearing. A high revving petrol engine will have higher numerical ratios than a diesel, multiplying torque but reducing speed. Most of the time, they will settle at a halfway house, allowing a reasonable amount of torque to be produced for a reasonable amount of time.
Notice that the two engines above have the same power, and when geared correctly, will perform the same. Power is often the best indicator of overall performance throughout the gears.
Back to the real world.... diesels are easier to drive and better for towing. The peak torque is low down in the RPM range, which gives a form of automatic speed control. If the speed drops, the torque increases, accelerating the car without driver intervention. It's also less effort to pull away - it's nigh on impossible to stall a diesel. Ease of driving, however equates to a boring drive, one that doesn't require skill. The noise is horrible as well, that Seat TDi sounds horrible until you give it loads of revs when the huge turbo drowns out the clattering. And find me a car that looks as good as a GT3 and is powered by a diesel...
