I,m confused, say you decided to side step several issues and went the supercharging route. Thus exhaust system back pressure is not a problem (you're supercharging because you want more power than
a normally aspirated lemans type p-port will provide). Do you want more or less overlap or is detonation more of a concern so retarding is the order of the day. cliff

On balance a supercharger sucks more power from the engine as it is not utilizing
any of the 50% of a gallon of gas waste energy in the exhaust. A turbo charger does
utilize some of that energy.

It takes HP to compress air. In the case of a supercharger that comes directly
and completely from the e-shaft. In a turbo charger most of the HP comes from
the exhaust with only a slight penalty in back pressure.

Let me put it this way. A 250 HP net output supercharged engine might be generating
300 HP internally. 50 of the HP is going into the supercharger. That 50 HP
also adds to the cooling requirements.

In a 250 HP net output turbo charged engine only about 10 HP or so is manifest in 
back pressure. That means the engines is only generating 260 HP internally.

Getting down to the problem of overlap. With a p-port exhaust and intake
you always have a lot of overlap due to the combustion chamber being in the face 
of the rotor. You won't affect the amount very much one way
or another no matter what the timing is. Timing in a p-port engine is way 
over rated when it comes to controlling over lap. What is far more
important is the length of the exhaust pipe and intake pipes. In that case
the exchange of gases between the exhaust and intake will be highly dependent on
RPM, the amount of boost and the  instantaneous pressure difference between 
intake and the exhaust. Gases flow from a high pressure area to a low pressure 
area. In a turbo or supercharged engines intake gases sometimes flow into
the exhaust area increasing the BSFC and sometimes they flow from the exhaust
to the intake affecting combustion stability.

To my knowledge nobody is measuring that pressure difference in real time.
In other words when the engine is running at 6000 RPM nobody really knows
what is going on millisecond by millisecond. Perhaps Mazda does.
 
Paul Lamar
 
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