Re: AUDI & Mercedes

["Richard Klein" <rklein@cris.com>]

On 17 Oct 95 at 10:45, Robert S. Cohen wrote:

> >        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.
> 
> That being said, there are alot of real-world engineering problems to be
> overcome in adding alot of valves. An example follows...
> 
> Yamaha motorcycle engines, for example, have 5 valves/cylinder, and have
> had for some time (in their homologated 4 cylinder engines). The design (to
> my very limited knowledge) requires a goodly amount of spark advance,
> exposing the engine to the heat of combustion for a longer period of time
> than less (no pun intended) advanced designs. This in turn requires more
> radiator area to pull the heat out. One of their factory
> (vance&hines/yamaha) racers was disqualified earlier this year for running
> a larger-than-stock radiator in his bike (FWIW, I believe he was winning
> regularly :-)). The engines are also slightly more complex (costly) than
> their 4 valve counterparts by virtue of the additional valve/valve train
> parts.
> 
Good answer.  Now for my $0.02.  :-)

Generally speaking, more, smaller valves flow better than fewer, 
larger valves because they can make more efficient use of the limited 
space in a combustion chamber; ie, you can get greater total valve 
area in the same size combustion chamber with more, smaller valves.  
Additionally, it gives designers greater flexibility in combustion 
chamber dynamics (they can array the valves around the spark plug, or 
do something else that they may think works better).  The individual 
valves (though not necessarily the whole valvetrain) are also lighter 
than larger valves, a fact that one of the Italian supercar makers 
(Ferrari, I think) is taking advantage of in their new 60-valve 
12-banger for an 8-grand-plus redline.  All I've ever driven are 
2-valve per cylinder cars, but I've heard that multi-valve engines 
sacrifice low-rpm torque for high-rpm horsepower.

YWIA
   -Rich
   '85 Audi 5ks
   '85 El Camino
    member Teamsters local 486