Originally Posted by Diputado

Need some advice on determining (or at least reasonably estimating) compression ratio in my engine. Here's the facts: It's a 1965 model 289 with factory heads, block has been bored .040 over, and it has aftermarket 10.5:1 comp. pistons. According to the guy who built the engine (2 owners back), he didn't mill the heads any, just "resurfaced" them to, as he said, "clean them up". Cam is a Crane and the builder can't remember exactly the specs...but said he "seems to recall" that it was around .508 lift/292 duration (couldn't find one matching this in the Crane catalog, though!). Anyway...what I'm not sure of is how much the overbore has changed the comp. ratio. Any ideas out there on what the actual CR of this engine might be?