The reason why the valve guide boss is like the way it is in the first place to to help draw heat out of the valves and into the water jacket. The less material there is on the boss, the less heat will transfer out of the valves. Too much heat in the valves ( especially the exhaust valve) and they will have a short life.

It works exactly the same way hot/cold spark plugs work. A short plug will run cooler, since more of the plug is in the water jacket. A long plug runs hotter, since most of the plug is in the chamber, and the heat does not transfer out of the plug as quickly.

Shaping the boss is OK, but removing too much material will start effecting the life of the valves.

If your only strip racing, should not be too much of a problem, since the engine block does not saturate with heat, nor does it run for extended periods of time.

Street Strip, your exhaust valves will be burt quickly, depending on how much of the boss is removed.

Also, there is a mechanical stability of the valve perfomance you will loose, and may get end deflection when the valve is not seated.

This will show up on the valve seat in the heads as a mashed appearance on the chamber side of the valve seat surface. Cause the valve is litterally not traveling in a straight line, because of the deflection.

Remember, just cause the boss is removed, you still have the valve shaft itself in the center of the port. The most gain from porting is the de-shrouding of the valve on the chamber side of the heads, and the short turn radius. Port matching is another place where some of the gains are made.

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66 Stang 385+ HP 306 .494 /.520 225 durr @.05, 200cc Windsor Sr's, Edle RPM, C4, 3.00 posi, 575 Annular Mighty Demon, 22 MPG,