I have 13brew rotor housings where I removed the exhaust sleeves and completely filled in the port....I think without warping the housing. (only time will tell). Now I like to cut my own exhaust ports. I am looking for maximum flow for a higher boost application. My intake ports are: almost stock primary, large secondaries and 1.25 inch peripherals. My intention is to machine a 1.75 to 2 inch round hole with an upward angle. Then I will grind the port wider and more rectangle shape towards the combustion chamber for a EO 80° BBDC

EC 65° ATDC. Any input interms of timing, shape and size would be highly appreciated.



Thanks

CW

good luck chief

the thread it is from.



Lasse Wankel on PP from evil forum



I believe you must design your exhaust port to flow exhaust out of it well, but do not forget to design it so that blocks the exhaust reversion wave from affecting port flow or entering the engine during the exhaust/intake overlap period.



The stock Mazda port inserts have an angled step at the top that largely makes up the expansion area of the port, I believe the pressure wave hits this and is reflected down away from the port opening.



It would seem to me to be even more critical on a turbo application where it is harder to adjust the exhaust runner lengths before the 1st restriction/collection. That is where the pressure wave will start reversion and that length is normally be tuned on the NA.

I agree with that theory but really don't know what to shoot for. These two objectives, optimizing exhaust flow towards the turbo and stopping the reversed pressure wave are almost contradicting. For sure Mazda wasn't concerned about the flow to the turbos since the exhaust sleeves expand rapidly and the gap between the exhaust opening to the sleeve both will slow down flow and add turbulence. Is the pressure wave more important than the better flow? Mazda might have thought so. Still, they were shooting for low end power, passing emissions, quiet exhaust and some 200 hp.