Re:TS = more power?

[christian147@domain.elided]

Ron Ewing writes:
>However, one wonders that if a TS is such a good idea for power and
>emissions why isn't it in wide use, esp on upper end cars?  

It simply isn't needed.  A pent-roof combustion chamber will do
everything that twin spark does in a high compression hemi, with less
complexity.  Pent-roof burns fast for among other reasons it has a lower
surface to volume ratio for a given compression ratio.  It should be free
from sharp convex edges (piston dome).  In short it for a given
compression ratio it should have a lower octane demand.  Modern road
engines have a max compression ratio based more on NOX production then
octane, and so don't have as much need to speed flame propagation up to
stop detonation.  The flame propagation speed in a good pent-roof chamber
negates most of the advantages of twin spark.  

 One thing I haven't seen mentioned is that compittions heads came in 60
and 90 degree versions.  The Alfetta  also had a 16 valve head with what
looks like a pent-roof, flat pistons and single plug.  The GTAm is also
listed with a 60 degree head, flat pistons and twin-spark which would
seem to indicate that ALFA used a lot less of a hemisphere on this
engine.  In the case of the Am, I'm left to feel that the twin spark is
primarly to allow larger valves.    

Chris Hall
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