i'm building a 31 chevy pickup for a daily driver. i'm pulling all the old drive train out and going with a 235 and a t-5 trans. i swaped the axels for a 53 pickup in the front and a 92 toyota 4x4 rear. this way i'll have hyd brakes and 6 hole wheels, and should be able to use my 6 hole stock wires. what i would like to know is. how much can i mill off the head to raise the compression to around 8.5-1 or 9-1. i would like to build a milage motor, so what should i do to get the best gas milage. would a mild cam grind like a tork grind help. let me know what you think

Hi badsix . . .

The guys from Delta Cams can re-grind pretty much whatever you want in terms of a profile. But everything is a tradeoff when it comes to a camshaft. Duration is great at higher RPM but it takes away from low end grunt - which has to be replaced by something - increased displacement/compression-ratio or both. So it is good that you are looking at this from more than one dimension.

As for milling to get C/R - it has its limits. Bill Fisher's book suggests that older design head would tolerate as much as an 1/8" (0.125) of milling - yielding an increase in .75 C/R over stock (because of the reduction in combustion chamber size). Not sure if the later design heads will tolerate this much milling . . .

The big downside with excess milling is that it messes with the geometry in the valve train. The rocker posts have to be shimmed an equal amount - followed by the valve springs to get the correct uncompressed height. I also don't see how the stock intake valve recess/seats would survive this much milling - which means additional machining to create a new recess for the value and then grind a new seat. And I would be worried about head bolts bottoming out . . .

A pop-up piston seems a much easier route to added C/R . . .

regards,
stock49

thanks 49 good info, i'm just after some good ideas on an engine build. maybe stock would be the way to go, this thing will never see any thing above 4000 rpms. i would think a little boost in the compression would'nt hurt anything though. i'll be going 30+ miles a day with it so i would like to get good milage if posible