A 455 has a bore of 4.151 and a stroke of 4.210. A 400 has a bore of 4.12 and a stroke of 3.75. 6X heads have huge chambers 110 CC (GRAPEFRUIT) bigger. #48 heads have volume of 72 cc (ORANGE).
You put grapefruit heads on a 400...7.8 compression, bad. You put grapefruit heads on a 455...eh, so so. 8.6 to 1
You put Orange heads on a 455..squish..need 110 octane. Orange heads on a 400, 100 octane.
It is all about area/volume when piston reaches TDC of the stroke. This area includes some ring area, valve relief cc, chamber volume and deck height clearance.
When I say read about it...it will be better if you had a diagram and read up on it rather than reading schmucks like me explain it.
In essence, most good heads are 72 cc..On a 400, they are fine with the proper piston and a blend of fuel if a stock piston.
The smaller the volume at TDC, the higher the compession, the higher the grade of fuel.
Si Vis Pacem Parabellum
1967 Starlight black PMD Engineering 400 Auto 1968 Alpine Blue 400 4 speed 1968 Verdoro Green 400 HO 4 speed 2013 1LE 2SS/RS Inferno Orange Camaro.
