Dyno testing a stock(?) 1972 440
From my point of view , having gone from a 14.9 second 96 mph Charger RT back in 1971 to an 8.70 drag car that runs 153 mph, There are certain rules that fall in line for best results. Minimum for a decent life and good power, bore it and hone with torque plates if you can. A loose piston to bore wears out rings in a hurry! If you can, pick pistons and rings that are narrow. If the move is free, so is the extra power. 1/16 would be great.
1- make it seal. As said above, if you don't build cylinder pressure, ya ain't gonna get any power!
2 make it flow, usually starting with exhaust. That helps the whole power range. On any performance build, good exhaust (headers+ good mufflers usually) will be the first big jump in performance given you have a healthy motor to start with.
3 Basic cylinder head improvement; fresh three angle valve job, back cut valves.
4 Proper cam for cylinder pressure, must be picked to keep cranking compression compatible with your final compression, head type, quench and lowest point you need torque. Don't make the mistake of trying to put a cam with more duration (more than say five to ten degrees over a factory HP 440 cam) in combination with a stock converter (low stall, say below 2400) or a stock gear ratio manual. You may get your butt handed to you by a stock Duster 318 with headers. It happened to me in 1971. I went by the guy like a freight train three hundred feet down the road, but he already had his victory!
5 Don't think the factory Thermo quad and steel intake need to go. Work with them. If you think I am wrong, check the stock class NHRA low compression cars' performance. I was into the twelves with the RT before I got rid of mine. If you plan to upgrade, untill you get above 500 hp, stick with a Performer RPM as your biggest choice in manifolds. Single planes are for a 4,000 and up launch, combined with a big cam. The rpm that the single plane passes the dual plane in power is 5,000. If you shift at 5500 ( I went 11.60s at 118 mph in a 440 duster shifting at 5500) you spend about three quarters of your time below 5,000 rpm, maybe more.
6 This is a torque motor- you won't run it above 5200 to 5800 until you get into some pretty serious cams and combos. Do everything you can to enhance torque. Long tube headers, long collectors (18-24 inch). Stay reasonable on tube size, 1 7/8 works well. On the rpm deal, My buddys 70 Chrysler New Yorker (gutted for racing) weighs 3800 race ready, uses a Mopar 590 cam and Eddy heads with 10.0 compression, shifts at 6200 and runs 10.90s all day long.