The #781 castings are not bad to work with on a budget, they are very close to the 049 castings. I have a (worked) pair on my boat engine. They were cast from 1973-85 with 2.06in & 1.72ex valve diameters and open combustion chamber sizes around 119cc's. Intake port volume is quite small so higher velocities can be achieved for low to mid range torque. I had the larger dia. valves installed 2.190 & 1.880 and cleaned up the bowls and opened up the intake and exhaust ports a bit along with port matching the tunnel ram. I'm using a JE piston with a dome volume of 23cc and along with bore & stroke, deck clearance & gasket volume my compression is 9.98:1. With a Comp Cams flat tappet cam and sound valvetrain this engine made 542hp @6,000rpm & 520tq @ 4,500rpm on the dyno back in Feb. This combo has worked fine for me and my jet boat has seen 77mph.

I have a question on the 781 heads! I have a 454 with mild cam, peanut port heads and holley 750dp carb, my question is, will I see a difference if I swap heads to the 781? Or do I need to change pistons to a higher comp. to see any real gains?


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I did the same thing, saw 2-300 rpm increase, 52 to 54-5500
Both were stock valve size.

Dan'l