i was looking for someone to explain the effects of torque and bhp whilst driving a car and if this means turbo diesels are better than petrols in more ways than just economy
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The most important thing is the total area of the graph under the torque curve, something you will have to measure yourself.
Stated figures are just "maximum" figures which aren't that important in real life.
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Here's a previous backroom attempt;
www.honestjohn.co.uk/forum/post/index.htm?t=24793&...f
Number_Cruncher
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Rather than focus on the definition of torque and BHP lets assumes that higher amounts of both are better. Taking say a 2ltr example of both a Turbo will produce much more torque though slightly less bhp however the real story is the useable powerband. A TD will pull like a train from 1500 rpm, produce it's maximum torque at under 2000 and max power at around 4000, where as a petrol will need to hit 3500 ish to produce it's max torque, and will only produce around 60% as much, and will not produce max power until around 6000 rpm.
Therefore the TD is much more gutsy at low revs though ultimately runs out of puff just as the petrol is getting into it stride however this is countered by the TD's ability to pull higher gear ratios.
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See this article about possible future developments in diesel engines: www.bankspower.com/Tech_dieselperf.cfm
Says if they can reduce the weight of engine components to increase maximum revs., then diesels could easily outperform petrol engines.
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But don't forget the important figure is torque at the wheels. So if a Td has lower (numerically) gearing, which they do, then the torque increase due to gearing will not be as great as on a petrol engined car with higher gearing. So if the gearing is 30%lower on a TD, then it will need 30% more torque at the crank than a similar petrol. That's why super torquey TD's never feel so much better than a petrol that the figures would suggest.
TD owners are always banging on about how low the revs are at 70mph, but it's all relative. If a TD is doing 2000rpm at 70, then that's nearly 50% of the max rev range. If a petrol engine is turning at 3000rpm for 70mph, then guess what, that's also about 50% of the max revs. As diesels are harsher and noisier, it works out about even as far as I can see. Personally, I couldn't care less if the engine was doing a million revs at 70, it's the ultimate NVH that counts.
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NVH? Wazzat please?
www.bayingbasset.com
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NVH = noise, vibration, harshness
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Diesels (some) are harsher at 4000: but not at 2000rpm. My experience is that not only are turbo-diesels quieter at cruising speed, they don't require anything other than gentle application of right foot to accelerate quickly from 2000. For petrol engines, 3500 is still in granny/rice pudding skin mode!
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Yeah but half the fun is touching the redline. The petrol's jsut getting going then!
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Fun?
Listening to the poor little beggar revving its underware off?
I used to think that, back when I was a pubescent schoolboy and had little mechanical sympathy. Disks in computers spinning rapidly to acquire or dispense information seemed cool too. Now I'm more impressed by chip memory which does the job with no moving parts - that's 21st century.
My ideal engine now would have no moving parts and be silent.
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Engines are meant to be revved and meant to be heard. At least petrols sounds nice!
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Hey Adam, you should come up here, we've got Dastek next door. Any excuse is a good excuse to go outside and listen to some piece of exotic (and not so exotic) machinery hit the red line on their rolling road.
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That's not a bad idea actually!
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