I have gmpp aluminum "fast Burn" heads on my 390 stroker sbc, this passage is taken gmpp's site........
Quote:
D shaped 78cc exhaust port and runners provide exceptional flow for applications well in excess of 500 horsepower.
Raised runner (.240 higher than conventional 23° head) intake ports with 210cc ports and runners provide exceptional flow for applications well in excess of 500 horsepower. Raising the top of the intake ports provides a better “line-of-sight” through the port and onto the back side of the intake valves.
The 62cc fast burn combustion chambers are the most efficient combustion chambers ever to be incorporated on a GM Performance Parts cylinder head. Their Fast Burn efficiency produces higher cylinder pressures by burning more of the available fuel before the piston starts its power stroke downward. Additionally, by more completely using the available fuel, the head ensures that an engine is producing more power for a given quantity of fuel.
The Fast Burn head’s specially designed valve seats will accommodate up to 2.02 intake valves and 1.600 exhaust valves. Their design also provides superior structural characteristics.
The 2.00 hollow stem lightweight intake valves are utilized to provide exceptional flow and intake charge velocity. Their light weight makes them suitable for sustained high RPM applications as well as reducing loads on valve springs, rocker arms, push rods, roller lifters and camshaft.
The 1.56” sodium filled lightweight exhaust valves have all the same great benefits of the hollow stem intake valves. In addition, they are able to perform in extremely high-temperature performance applications.
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Interesting that they only use the sodium filled stems on the exhaust. I have not broken one yet, and they really rev.
Dan