The Truth about 318s

The best stock configuration 318s from a compression point of view are the 67-70 models with a rated compression of 9.2:1. After that, heads got larger chambers and pistons sunk further down into the block. The deviations from this trend were the 318 lean burn (302 heads) and the 318 cop car motor (360 heads).

The combination of a 68 piston and a 302 head that I have in the Demon gives an actual compression ratio of 9.3:1. Even at this compression ratio it is easy to "over cam" the engine, particularly if stock rear gears are used.

Comp Cams publishes a chart that recommends different camshafts based on compression ratio, vehicle weight, and rear gearing among its factors for consideration. I consulted it after building the engine for the Demon and determined I need more rear gear to get the best out of my engine set up.

Wiesco and Keith Black produce 318 pistons that will elevate compression from the low 9s to the low 10s depending on the combustion chamber cc used. Heads can be milled to decrease combustion chamber cc but sometimes introduces sealing problems with the block and/or intake.

At the end of the day, the 318 is what it is. More power is available for less with a 340, 360, or a big block. (It would be interesting to see how a built 360 compares with a 361 B motor.) The higher initial cost of the larger engine is more than offset by the cost of modifying the 318 to produce giant killer results.