[jluetjen]

I'll share with you what I do know and you can draw your own conclusions. I'm not sure that I'm a specialist rather then an analyst of data that others have published.

* 2.2S heads flow more then enough air for over 210+ HP (as used in the 2.7RS) or more in the case of smaller capacity engines. Getting more then 210 HP from a 2.2 puts you in the realm of full-race motors which don't have great drivability at low rev's and poor gas mileage.
* 2.2 T/E heads (which you don't have) flow enough for about 165-180 HP. In their case it might help, but consider the following...
* In general, Porsche's ports get wider as they approach the corner and the valve guides. As a result, even with the valve guide protruding, the cross sectional area of the port does not appear to be a constraint. You could actually make the head's performance worse by making the cross section too great in that area of the port and thus lose your intake velocity. This could very well be the case if the constraint is actually elsewhere in the port as it appears to be in the T/E heads.

My suggestion -- don't bother changing the valve guides. Reducing their length will most likely reduce your valve or valve guide life some (since the lateral (rocking) forces on the valve will be distributed over a smaller area) without any worth while improvement in engine performance. If this were a Spitfire motor, the answer would most likely be very different, but it's a Porsche motor and all of the data suggests that Porsche's engineers really had their motors figured out pretty well.