Engine Build For 1970 Duster
Sounds like a 350-360 hp engine
400 hp is more like 10:1, 235 @ fifty cam, air gap 750, headers with 200-220 cfm heads.
And
@Dust Ya
400 hp is a 12 second capable car if it is not too heavy.
Id drop the ratio a half point. It’ll be a little easy with the best octane available. Even if you have 93 in town.
9.5-1, LD-340, 750 cfm carb, a mechanical cam @ 240@050 or a hydraulic cam at 248@050. Heads should be bowl ported. Gasket matching a plus but not mandatory.
If I was doing new pistons, I’d use the KB-107’s just below zero deck and a head gasket thickness to get the 9.5-1 ratio. These pistons at zero deck and 72cc J heads with a .038 head gasket deliver a 9.8-1 ratio. I have done this before. (With a .030 overbored 360.) But you need to check, measure and be sure of everything.
Back when I did this, I also had a LD-340 with the MP mods for the milled divider and a TQ hog out, MP Purple 292/.509 hyd. cam and super comp headers at 1-3/4 into a 2-1/2 exhaust. Same heads and it was a zero deck piston engine.
(Backed by a 4spe and 4.10 gears.)