stephen_gusterson
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| posted on 4/3/03 at 12:44 AM |
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craig
the gearing thing was a good point. However, diesel engines gernerally produce a LOT more torque - quite often x2, so you are still up on things even
with lower revs.
There has got to be summat going for higher torque, or trucks would run on petrol ....... i dont think its just fuel / efficiency
atb
steve
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craig1410
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| posted on 4/3/03 at 09:03 PM |
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Hi again,
Sorry to start this one again 
I think that there are two reasons that trucks use diesel and I have to disagree with you by saying that the first reason is fuel efficiency. Haulage
companies are always the first to complain about fuel prices because it hits them directly and is one of their biggest costs.
The second reason is tractability and is the reason I'm building a Locost with a V8 and not a 'bike engine. A truck engine operates in a very narrow
rev band and the engine is tuned to give max torque in that band at the expense of anything outside. To haul 40 tons up a hill you need controllable
torque not racy power and a slipping clutch. However you could achieve the same thing by using low gear ratio's and a petrol engine. A bike engine is
at the opposite end of this scale, tuned to operate at high RPM's but with no real torque low down. The Rover V8 is somewhere in the middle of these
two IMHO.
I should mention that I was involved in the design of the Common Rail diesel injection system during my time with Lucas Automotive in Cirencester and
I once had an excellent explanation on diesel engines and why they have lots of peak torque and not much power.
The answer I was given was that diesel combustion produces a huge "pulse" of torque just after combustion (due to very high compression ratio and
fast burn rate) but this fades away very quickly and since diesel doesn't have as much chemical energy as petrol the average power gained from a
given capacity is less. This very high torque pulse is why the engines are built out of very heavy cast iron and as a result, the weight of the
pistons and rods prevent high RPM's.
Hope this helps,
Craig.
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Browser
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| posted on 5/3/03 at 02:22 PM |
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Just to get the thread back on track, I have posted else where on this but, Citroen/Peugeot XU 8/16 valve. Modern design, all alloy, 130/160-oddbhp in
standard trim. Have a look at http://www.pumaracing.co.uk/ who does tuning bits for them and tells you how to tune them as well!
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