Again I say, hook up a vaccume gauge, go for a drive then report back what your vaccume was at cruise.

My 318 held 17 inches at 70 mph cruise. A piston area of 10.65716 pulling 17 inches of vaccume is 181.1717 inches of vaccume on each cylinder X 8 almost 1500 inches vaccume being pulled every other revolution of the crank, that is far from nothing. Again I am not saying the fight against compression is insignificant but the vaccume loss is huge also. Compressing air that is under 17plus inches vaccume into an area 1/10 the size it was is not hard when you have 14 PSI (atmospheric preasure)or so pushing the bottom of the piston up. Someone a little more mathmatically gifted than me can convert it to LBS for you so you can see how much it really takes to pull those pistons down, you WILL be suprised. I know when someone showed me I was totally shocked