Auto Racing: Valve seats, combustion chambers, cutting angles

Question
Hello Matt, hope to get some tips from you about getting more engine horse-power by correctly cutting valve seats in the cylinder heads. In most cases, I have read that the correct cutting angles are 30 degree starting from the combustion chamber leading into the port, then 45 degree at the lip and then even a 60 degree cut before the throat. (Some say 31 degree and 46 degree and 61 degree; why the additional increment I cannot understand). All these will result in greater gas flow. Is this treatment for the intake valves only or does this also apply to the exhaust valves? Finally, will the valves have to be re-surfaced with the appropriate angles too? Will it help further to re-shape the stem and the area just below the valve head?

Answer
Valve angles have a significant effect on flow when matched to the proper cylinder head design. Angles vary depending on the intended use of the engine. For intakes, a narrow seat is best because it has less restriction therefore providing better flow. Exhaust seats need to be kept wider to allow for heat transfer from the valve head to the seat. Otherwise the valve will burn and warp causing compression loss.
The key here is to match your intake gaskets to the cylinder head, keep the intake runner straight as possible but do not polish it. A rough surface keeps the fuel in suspension. Polishing of the combustion chambers is mainly done to prevent carbon build up and detonation. On the exhaust side I would make the exhaust port slightly smaller than the gasket to prevent backflow or reversion. Concentrate on the short side radius of the exhaust port which is where the majority of the gains will be found.
Hardened seats and stainless valves are a must with today's gas. Contouring of the transition from the valve head to the stem can also show some high rpm improvement.