Its all a bit more complicated than most people would think. The 944 head is at a disadvantage compared to the 928 head, normally this is not the case. The 944 intake valve is positioned closer to the bore than in the 928 head. This shrouds the valve and this is quite an issue. We were getting big gains when we experimented by moving the valve away from the bore.

In my research into a truly big valve head with a big bore (109 mm) it indicated flow of around 350 cfm at high lifts. N.B I have only tested a 53.34 mm valve in a 103 mm bore and the best result is a touch over 300 cfm @ 0.500". That head had stock 928 valve position.

The big valve head will be a 55.88 mm in the 2.7 litre head and running radius hydraulic tappets with around 16 mm lift. When I extrapolate the results from previous testing adding in the movement of the valves away from the bore albeit the exhaust gets a touch closer to the bore therefor 350 cfm seems is quite reasonable.

Back to the 48 mm valve, here's our development;

https://rennlist.com/forums/928-foru...fold-test.html