Havent decided what we will call these heads, but they must be used with a 6.1 intake manifold. The 5.7 intake window has been revised to accomodate the larger intake runners of the 6.1 manifold. It is recomended to use these heads with the 6.1 intake on our 392 stroker motors. The heads flow over 340cfm's, so it is advised to have the 6.1 manifold ported as well. With almost as much total flow as our ported 6.1 heads along with a higher port velocity, we may try these out on a 426 as well to see what the differences are.
For those of you that do not know the differences in the intake windows, here is a picture of the 5.7 and 6.1 head side by side.
Tim C