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Chris, The main restriction on the 77 gas intake system is the inlet to the manifold (where the carb attaches). You can expect to lose 20 to 30% flow with the manifold. A stock 77 head with a 1.31 diameter intake valve will flow around 51 to 53 cfm at 10 inches H2O delta P at 0.300 valve lift. A 'best' ported head (no major surgery) with 1.50 intake valves will flow 73 cfm, a 50% increase. But as I tell all my customers, the piston sees more than the cylinder head. It sees the whole tract from carb to valve seat, so a good flowing head with a poor manifold will still leave you disappointed. I need more info to point you in the right direction, like RPM where you want peak power, and your engine size. If you are limited to say 20% over RPM and you are 249 cubes (3.75 x 3.75), you should be at 55HP at 2250RPM with everything else stock. On the far end, with open RPM and same cubes, I can get you 125 HP at 3800RPM with correct match of head, manifold, and carb. For this power level, you'll need at least a carb with a 1.625 throttle plate and 1.25 venturi. Good luck with your Oliver!
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