Slant six single, to slant six double.

michiganpat said

what's the theory for less exhaust duration compared to intake duration for the slant? seems counter to pretty much everything you see cam wise nowadays?

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That’s due to the severely limited intake port on the slant. The head was designed for 170 cubic inches with a short stroke, and was originally designed in aluminum. That means huge coolant passages but not a lot of room for porting and reshaping the port before you get into water.

Doug was the forefather of Reverse Dual Pattern cam testing in the slant six world. He swears by them but I haven’t seen anything showing hp gains or losses over a traditional grind.