Pulse Converter Theory

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In a message dated 98-06-14 10:57:12 EDT, graydon writes:

<< My evaluation of the manifold is that the inlets are slightly restricted, 
> the mid section (or the runners to the collector) aren't bad, but the 
> outlet collector is very restricted.   Particularly if the pulses do not 
> arrive at teh collector in sequence.   If they arrive in groups (as I 
> suspect they do from a rudimentary calculation) then that collector will 
> be the greatest restriction in the whol exhaust system IMHO. >>

Be careful here Graydon.  Pulse theory of exhaust has little to do with
sequence or grouping (that's a runner length calculation, already done for you
by audi).  Pulse theory and collectors have to do with the relationship of the
AREA of the effective valve area, the runners, the nozzle and the collector/s.
If, after the calculation of these relationships, you determine that
increasing collector size is necessary, not so sure that the triple fins are
where I'd be looking.

Before you go forward with this 'thinking' I'd make sure it has sound
calculations behind it.  The EM (especially the 2 piece) is a good device as
it sits.  Remember, you want exhaust VELOCITY, higher velocity means more
energy to spin the turbine.  Velocity is more a function of HEAT than of
volume.  You increase volume, you decrease velocity.   You increase heat,
given volume, you increase velocity.   Can you improve what is there?  I
suppose you could, buying the 2 piece exhaust manifold gets you the most.  But
'restriction' isn't necessarily a bad thing.  Betcha higher gains could be
measured addressing upping heat for velocity than messing with any
'restrictions'.  Neither significant *given* the stock EM's.

Pulse converter theory is hardly a simple task, nor maximizing formulas
routinely shared.  A turbocharger application only compounds the importance.
I would encourage a whole new EM design (which for equal length runners would
probably require relocation of the turbo), before I'd mess with what audi gave
you.  But then, you have increased runner length which means heat becomes a
higher priority for maximum velocity.  Given all the compromises involved, I'm
not sure that 'gains' would be an all encompassing term.

Given the art of designing a pulse converter is still about equal to the
science, and just about all the 'actual' empirical data and testing
proprietary, a lot of time could be spent making a lot of wrongs, before
getting close to right, and maybe never 'better'.  Without a dyno to test and
measure each changed variable, a lot of time could easily equal a lot of
nothing.   Here, I'd give audi the BOD on the EM design and go to other places
for real and measureable gains.  

My .02

Scott Justusson