Peter
D3 heads require a minimum bore diameter of 4.090 inches; and there are no off-the-shelf intake manifolds for D3 heads, they must be custom manufactured.
They come out of the box in a very raw condition, allowing each professional race team to design the heads for their own application. Many of those applications are NASCAR racing ... where the engines have 3.40" stroke crankshafts and are operating at 9000 rpm (5100 fpm mean piston speed), and the combustion chambers are designed for low volume and high compression ratios. So if you purchase used D3 heads, that's going to be what is mostly available.
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