What size ports would one use on this 3.4 ?

[YTNUKLR]

What ports to use on this 3.4 engine?
3.2 case
3.3T oil pump
3.2 crank/rods
Bored 3.2 cyls to 98mm, 98mm JE's @ ~10:1
3.2 heads
Single-plug
Weber 46 IDA 3C carbs
Heat exchangers/muffler
906 cams

[Henry Schmidt]

3.2 heads are 41.5 +or- intake and 38.5 +or- exhaust. Unless you're planing on changing the valve size your ports are as big as you need. There is only so much air you can move past a valve so I use the 85% rule for normally aspirated race engines. The port size should never be more than 85% of the valve size. Any larger and you will actually loose performance.

PS: This is not a criticism, this looks like a great combo but how did you decide on 906 cams for this engine? Don't get me wrong "I like the 906 cam in small hi-revving engines" however, the 74.4 crank is not happy at higher RPMs and the 906 cam is only happy at high end. This seems a contradiction in the mating performance components.
Perhaps a cam with more lift and less duration would be a happier combination. The Elgin DC80 perhaps?

[YTNUKLR]

Well, I was thinking 911S cams, for solid performance across the powerband, but after riding in pwd72S's 72S, I loved the rush of the S cams at ~5k rpm and would want to duplicate it in an even bigger engine. So....I thought 906 (or RSR). Thanks for the advice Henry !

[KobaltBlau]

Ah, but your valves (and other stuff) are bigger. So to duplicate the rush of a 72S powerband, you can still use the "S" cams, or even better, Elgin's "Mod S" cams. In other words, you don't necessarily need a "hotter" cam for the same effect in a bigger engine.