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Milling the head for more compression?

Thread starter Don Pearsall
Start date Sep 9, 2020

Guest

Oct 13, 2020

stetracer said:
unless you recut the valve deeper in the seats also.
I have a 1150 head with .105? milled off and the valves cut .040? deeper in the seats. This is on a street bike.

Seating the valves deeper does increase the valve to piston clearance. But what is important with seating the valve deeper into the head, whatever dimension you seat the valve deeper by. is removed from the height of the fully open valve in relation to the combustion chamber roof. In other words seating the valves .040" deeper gives you a fully open valve that is .040" closer to the roof of the chamber. The valve still travels the same distance, but it starts from behind in relation to how far it is away from the roof of the combustion chamber. Getting the party started at high RPM's can be effected by a valve not open as far into the combustion chamber. Only a dyno or flow bench can tell you how this effects your setup.