When I run the nominal numbers (.020 deck, .039 gasket, 75CC chamber, 6CC piston dish) I get 9.64 compression for a '69 400. Take deck to .010" and compression goes to 9.85.
I'd bet the actual compression ratio of the early 400s was in the 9.55 to 9.8:1 range. The 10.5:1 was blueprint best case. I have been noticing that the R45S were almost bone white with AFRs in the 14.x-13.x during cruise. Which I thought was odd that the plugs would be that clean when running a double pumper with 70/79 jets and 64 PVCR.... E10 93 octane.
Looks like I'll be moving to the XR5s. Will moving to cooler plugs allow the curve to come in a bit quicker? I'm all in by 3500 RPM. Its an older build in a hot climate and I don't want to set the tune on kill.
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I could explain all this to the girl at the parts store, but she'd probably call the asylum.
White '67 LeMans 407/TH350/Ford 3.89... RIP
Red '67 LeMans. 407/TH400/Ford 3.25
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