Makes me wish I took some classes, but I figure I could bug folks on here for a little help. When boaring a motor, how does one tell the new displacement? I know .40 over on a 390 Ford isn't 430, so what's the math that's involved to figure out this? Nosurf was telling me a bit about it... something about timesing the overbore by the stroke... something to that effect. I've just been interested in finding this out for general knowledge... if folks arn't sure, anyone know of a good website or book that explains it well?
Uh, bore X bore X stroke X .7854 X # of cylinders Example: 3.498" X 3.498" X 3.8125" X .7854 X 2= 73.347 cu. in. -Jesse
A cultural-historical note here: In the fifties and back, most engines like flatheads, Olds V8's, and Chrysler hemis were capable of HUGE overbores. Even early SBC's could go 1/8" over. Rodders ignored the displacement results of minor overbores in their discussions, so that a 303 Olds bored 030 was still referred to as a 303. Only a bore beyond normal rebuild specs was worthy of notice and changed nomenclature: 283 Chevy plus 030 was still a 283; 283 over an eighth was a real rodders change, and so reclassified as a "301". Nowadays, most engines are only capable of surviving minimal reboring, and all changes are noted--an 030 350 is usually noted as a 355.
The Jalopy Journal
