How fast can you go with a Magnum? Who has the quickest setup?

The R/T cast iron heads from Mopar have been out of production for a while and are not worth looking for since they are really no better than currently available EQ heads. The R/T heads, EQ heads, and factory original magnum heads all have very similar lift limitations. They all require cutting down the guides for sufficient clearance and none suffer any negative results from this cutting down of the guides. Also, since it comes up occasionally, I just recently measured clearances on a 1999 magnum 360 with original stock pistons, heads, and valves. No modifications were performed at all except installation of Hughes cam SER1418ALM-10 and their retainers and locks. I used light checking springs for this and found right at .550" test lift the intake retainers contact the factory style valve stem seals. The exhaust retainer contacted the seal at .540" test lift. This is why the old 380hp crate motors had odd cam specs; Mopar never shortened the guides, they just installed a cam that fit the clearance. I had the guides machined down .100" on my heads to fix that clearance, then tested valve to piston clearance with the Hughes cam. Intake valve to piston clearance measures.090" with zero valve lash and no head gasket installed. The exhaust valve to piston clearance measures .200" with zero lash and no head gasket installed. Since everyone uses different head gasket thicknesses during assembly, I gave the measurements without gaskets installed. Once the guides are cut down for lift clearance and retainer to guide clearance, the main limiting factors on the magnum engines are the narrow ports at the pushrod pinch area, and that goes for all available versions in cast iron. However, as many guys and shops have already proven, well sorted parts combinations easily provide enough power to find the limitations of the factory block, usually well past the 500hp mark. There is no need to second-guess a magnum setup for a strong street or bracket engine.