how much of a power improvment can i expect if i mill the head .100 and put in the bigger 1.70 and 1.44 valves and mildly porting the runners? also does anyone have any tips for porting (what to do/what not to do? thank you

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1975 Plymouth Duster,225/6 2bbl. and duels, 904, 7 1/4
1986 Dodge Charger Shelby, 2.2 Turbo I, A525

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I wanted to up my slant six about a month ago. I started looking for parts and gathering info and I've leaned towards freeing up as much power in the head and intake/exhaust. I've got oversized valves which will help with performance and plan to mill the head to run premium (92) octane at 10/11:1.
Porting and polishing has been a trick used in my family excessively. We usually get a set of practice heads and port till you bleed water. For a slanter this is not the case at all. This is the one engine you want to merely have a light touch, which allows a amatuer to port and polish without hitting a water jacket. I took out as much flaws as possible and merely opened up the intake and exhaust with the rotary stone. Next you want to clean up the intake with an 80 grit, but allow some grittery to the metal which helps the fuel/air on a molecule level. Next clean up the chamber to a perfect sheen, and the exhaust.
My last suggestion would be to up the cam pretty signifactly from the stock. I got a custom one grinded from oregon Cam, however, anything around 260-270 with .444 lift is a great power maker. I would guesstimate around 200ish hp from all this with a super six setup.

can i use my stock cam? it the supposledy good one used in the mid 70's

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1975 Plymouth Duster,225/6 2bbl. and duels, 904, 7 1/4
1986 Dodge Charger Shelby, 2.2 Turbo I, A525