Thanks Lynn - that corresponds to what we discussed previously and sounds logical.

Now the other question - given what you have just stated, is there a need for a larger exhaust like the Turbo housing exhaust for the mild 38mm PP

The exhaust port provided in the factory 12A Pport housings is just about square with rather sharp edges. Little attempt is made to improve the port beyond that. So if say 270 HP at 9,800 is all you need, then that will be enough exhaust port. This is for a virtually unmuffled engine with well tuned exhaust system. Above 10,000 RPM the already large rectangular port intake port is enlarged and the round runner is enlarged. The exhaust is enlarged and radiused all around. The power is over 300 and the exhaust port is open some incredibly short time, and still works.  

 

At aircraft RPM there is little need to get exotic with the exhaust. If the new die grinder needs a workout, just radius the sides a bit. The opening line more. Then polish anything the exhaust flow will touch to look like chrome.

 

Lynn E. Hanover