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Re: AUDI & Mercedes

Benjawan Kuecharoenwong sez:
> 	While Audi developing 5 valve/cylinder ,the Mercedes's new line 
> engines are 3 valve/cylinder ,including the new v-6 v-8 in the future
> 	why...?? whose idea is better ?

"Better" will depend on your perspective: are you interested in pure performance,
cost, reliability, weight, complication, or whatever.

>From a pure performance perspective, the 5v/c approach is likely the winner.
However, it has drawbacks over the 3v/c in the area of cost (more parts, tighter
tollerances, harder to engineer correctly), packaging (more space used),
weight (valve train weight, an issue if you are looking to very high revs --
the cost starts going up exponentially as you desire higher RPM limits, 'cause
you have to go to exotic things like Ti springs, etc), and likely reliability/
service interval (need to keep all those valves operating in a narrower
tollerance region) if all else is equal.

Of course, all else is never equal, so the above does not imply that the MB
approach will be inferior in terms of power, and superior in all other
dimensions.  In the end, it all comes down to money -- is the engineering/production
money better spent on 5v/c, or somewhere else in the powertrain?  Audi is clearly
betting on 5v/c, while MB is betting on elsewhere.

Personally, I would like to see a 12-cylinder, 5v/cylinder desmo valve train,
entirely fabbed from Ti, with a red line of 20k RPM or so -- your basic Otto
engine-cum-turbine.  But not likely in this lifetime...!

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