tonytaylor

This is apparently more true for the 993 heads. I believe 9M was having difficulty getting the same power as the 964 Motec/Motec +1 conversions with the 993 and hence the solution of new heads, which is a cheaper option £ per bhp than a rebuilt 993 head with the required porting work ( since the 9M heads give more power in any case)

Red rooster

Tonytaylor,
I did not know that there was that much difference between 964 and 993 head porting .
I know that my motor , 285 993 , has bigger valves , so I guess different ports ??

Maybe a 911 Head expert can tell us ???

Geoff

Geoffrey

A 964 head has a 41mm port and a 993 head has a 43mm port so it is larger, however the air velocity is slower, especially on the 95 head which has the same size valves as the 964. If you measure the port volume the 993 is significantly larger all of which slows the air. The 96-on 993 heads have larger valves, the RS has larger yet, and teh RSR sprint engines have 54mm intake valves. All RSRs have 45mm ports. 993 have 8mm valve stems where 964 has 9mm valve stems which cause additional restriction over 8mm. 9M heads have are designed for 8mm valves. In all of the replacenment heads I do, I use 8mm.

Chris M.

No I don't have them but the link I provided was to a thread about Rennlist user Robin 993 c2 that has them.

c