In article ,
The Natural Philosopher wrote:
Quite the contrary. Variable valve timing raises efficiency

Er..only from a woefully low figure that a straight timed fast revving
engine has.

Isn't that the idea? You get the benefit of a powerful engine when you
need that power, but still have tractability in the form of decent low rev
torque and better efficiency. Have you ever driven essentially the same
engine with and without variable valve timing? I have, and it's a
revelation.


VVT allows a 'racing' engine to perate efficiently when not 'racing' It
doesn't overall do anything that tuning the engine more modestlly would
allow in the first place, other than develop more power without spitting
unburbnt fuel out the exhaust at lower RPM.

Err, if you're happy with an engine that has a poor power output then fair
enough. But variable timing gives you the choice - it's up to you whether
you use the extra performance at high revs.

and allows good manners at low speeds. And more sophisticated
variations which get rid of the throttle on petrol engines will raise
efficiency further.

Superchargers on the other hand always waste fuel.

Not necessarily either. If you can increae peak peressures and combustion
temperatures you can actually gain efficiency. However thats not the way
they are set up on road cars.

Then what is their point in this discussion about road cars? Unless you're
suggesting hybrids will appear in racing cars?

--
*Go the extra mile. It makes your boss look like an incompetent slacker *

Dave Plowman London SW
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