• How has the weather been in your neck of the woods?
    We are looking for feedback from our membership to see how/what the weather has been like in your area. Please Click here to take our Winter Weather Survey, we would appreciate it.

heads and compression?


LawnSite Member
Anyone know what the stock heads on a 91 4 bolt block 350 motor are? What is the CC and what compression would that yield using a set of flat tops? The stock pistons are valve and otherwise relieved to produce somethinglike 8:1 compression for the big trucks right??


John DiMartino

LawnSite Silver Member
A 91 4 bolt block is more than likely from a truck,an 8600-14500GVWR truck.These are not good heads for performance use if thats your intentions.Use the LD heads or car heads instead.The HD truck heads have smaller valves and thicker valve stems for durability,these motors are meant to hold up for extended full throttle operation during heavy towing/hauling.They do not have as much power as the light duty heads that have bigger valves,thinner stems and higher compression.If your looking for durability over power,use the HD truck heads.


LawnSite Member
Yes the heads are from a HD type motor was in a 1 ton commercial van, I had them cleaned up using stock valves, and pocket ported, they seem ok, I don't run up over 5K anyway, but I'm curious as to what my compression would be if I changed to new style vortec heads with the 64cc chamber. The compression on my 355 was supposed to be 9:1 with the stock heads and block which were not milled, I don't think it will run on 89 gas with anything more than that unless the timing or gap is lower.