Multi-valve engines (was: Re: AUDI & Mercedes)

[rdh@sli.com (Robert D. Houk)]

   >        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 ?

   The idea behind adding more valves to cylinder heads is to allow the engine
   to breath in and out more efficiently.

In particular, and to a zeroth-order approximation, the most important
contributor to "efficient breathing" is total valve circumference (which
is not to outright dismiss other factors like lift, duration, overlap,
manifold geometry, etc, and so forth) -- you get more total circumfer-
ence with many small valves than with few large valves (consider embed-
ding circles within circles...), and thus more "total breathing". Also
small valves have less mass, and thus accellerate at higher rates, so
you can run the engine at higher rpms (modulo crankshaft/piston/rings
etc. and so forth).

					-RDH