Mr Helmholz - simple model

[Gary Derian]

A megaphone works like a variable length pipe.  High frequencies reflect
back close in and low frequencies reflect back more towards the larger end.
This broadens the sweet spot.  2 stroke engines work very differently.  The
first part, the diverging area, of the expansion chamber reflects a negative
pressure wave to suck the air fuel charge into the exhaust while the
transfer ports are still open.  This extends the intake cycle.  The second
part, the converging area, reflects back a positive pressure wave to push it
back in after the transfer ports close but the exhaust is still open.  A
properly tuned pipe makes a 50% to 70%  improvement in power.

Did the Mercedes actually have a 2 stroke style expansion chamber or were
they megaphones with little converging sections at the very end.  Grand Prix
motorcycles have used diverging/converging megaphones since the 60's but
they are not the same as 2 stroke expansion chambers.

Gary Derian <gderian at oh.verio.com>

> >If this opens a whole new box of problems, just ignore.  But, I've
noticed
> >what a huge change expansion chambers have had of VE in 2 strokes, and
after
> >seeing the Mercedes Benz GT (Sedan, whatever they call em) with the v-6,
and
> >3 into 1 exhausts, and running 2 expansion chambers (one per side), I
just
> >wonder, how they came up with that...
> >   Is it the shape of the cones or volume that makes a "E.C." work, or
> >both?.
> >Grumpy
> >
>
> Both. Megaphones convert velocity to static pressure pretty efficiently.
>
> Greg
>