Ed Anderson wrote:

>
> > Not directly applicable here except in the sense that we should make

>
>> untested assumptions, but here goes:
>>
>> Kent Paser of 'Speed with Economy' fame played with 'reversion cones'
>> on his Lyc. They are cones smaller in diameter than the exhaust ports
>> & mounted directly in the ports. Obviously this should interfere with
>> exhaust flow but he found that they can improve breathing in a Lyc.
>>
>> The NA splitters look suspiciously like flattened cones....
>>
>> To invert Bob's tag line: when things change, things change.
>>
>> Charlie
>> (just stirring the pot a little)
>>
>
> Ok, "Pot Stirrer"{:>).  The reversion cones in exhaust are designed to
> do just that as you are aware.  Prevent the reflected pressure wave in
> the exhaust from pressurizing the cylinder while it is open for the
> intake function and hindering intake of fresh fuel/air. However the
> only  Mazda engineering data that I could find indicated the primary
> purpose of the "splitters" are for noise suppression. Here are two
> charts on the Mazda Exhaust splitters.  The technique appears to be
> more effective at the higher rpms and as Tracy and I speculated,
> probably has little effect on power until the higher rpms.  From the
> chart, it looks like the technique is really effective after 4000
> rpm.  So if it is at the same time affecting power, it may be
> happening at lower rpms than I originally would have thought.  Here
> are the two charts.
>
> 7-207.gif shows the splitters  and 7-208 shows the 8 db noise
> reduction obtained by use of the splitters.  I believe the tuboblock
> has no splitters because it has the turbo to deaden the exhaust noise
> - if the splitter were for reversion prevention then I would think the
> turbo blocks would have it as well.
>
> Not conclusive proof, but the only data I could find on the function
> of the splitters.
>
> Ed A


I love it when a plan comes together. I got Ed to show me previously
unseen hard data on how effective the splitters are at noise reduction.
:-) Now I need to know how much hp is really lost. In order to determine
that, I need 1st to know how the difference *using the same exhaust
system*. Then I need to know how much is lost in the extra 'muffling'
needed to reduce the clean ported system by 8 dB. Then I need to know
how much weight is added by the extra 'muffling'. Then how much drag is
added by the extra muffling hanging out in the airstream.  I think Tracy
said that his current belly mounted muffler is costing somewhere between
3-5 mph. Looking at the cube function of airspeed/hp, how many hp does
it take to recover 5 mph at 200 mph? Can I arrive at the same net
performance with a smaller in-cowl muffler & some careful heat shielding?

BTW, Bill's right about the name & design details (expanded pipe around
the cone) of Anti-reversion cones. Again, a plan comes together as I
learned more new stuff. I knew the design details but wasn't aware of
Jim Fueling. Thanks, Bill.

Sometimes dumb questions (or statements) yield some pretty intelligent
thoughts & useful data. Onward, through the fog...

Charlie