Will a Mummert manifold and the best car headers add any performance to a stock 312? Motor has ecz-g heads, 1.54  rockers, the better exhaust manifolds, Holley 4150. Not sure on bore size, or cam specs but assume cam is stock.  If I can buy 25 HP and some torque it would be worth it, for 10 HP probably not.  Any thoughts appreciated, I've been thru the Eaton test pages (amazing) but none really test an otherwise stock engine so I'd be blind guessing any value.  Thanks

Ted, Redding, CA

I would say at least 25 horses. Probably more. Headers alone probably worth that and they will also increase gas milage. Are you planing on changing the carb as well as the intake? Existing carb should work fine. Biger carb will give more power. I am thinking 600 CFM would be max for stock cam. 550 may work better.