Factory Magnum Heads

dg,
Did they say what they had in the heads for valves? Because from what I've found they may have went the wrong way on them.

IMO I would gasket match and bowl blend the heads and leave it at that, use stock size valves and do some machining on them. Port the exhaust, but this isn't totally necessary as 70% exh. flow is all that really is needed to make the engine perform, and less on the street. So IMO I would use these heads if the engine already had them, as the cost to swap them over may not be worth the gain that you may want or get.

These heads don't respond like the older LA heads do when opened up for larger valves. Sure most all heads will lose some flow in the low lifts when a larger valve is installed but the high lifts should be better, and in this case it was worse. Larger valves only gain about 5% in the upper lifts and lose this in the lower lifts so use the valve size for the amount of cam used. Upper lifts being .600 and up. As can be seen in the flow #'s that at .500 they get to be about even. From .100 to .500 it's the valve job that makes the port work and is the most important, after .500 the port itself takes over and the valve job becomes less effective. In the case of the 2.055 valve the chamber and the cylinder becomes the restriction. Even if the chamber is relieved the cylinder wont be, so the need to do this may be hurting the flow some as the air flow would be running into the cylinder wall.

So in my overall opinion on this casting, if the R/T is better then this may be the way to go but if it isn't then give me old iron. This head was worse than a 587 head with minor work done and a smaller valve. And only even to a 576 head out of the box.

This is what the head flowed with a 2.02 untouched,

.100 79
.200 132
.300 198
.400 225
.500 224
.600 224

So as we can see the magnum head is suffering a good bit due to the port shape and cross sectional area. So being that the CSA is small the smaller valve works better and thus would be the best choice.