If I understand you correctly , then yes.
A loss of 2cc in the head will equal a gain of 2cc on the bore.
But
an overbore is a GAIN of cc in Swept volume, making it a Net gain to the Compression Ratio.
Here's what I mean;
at 3.91 bore, the swept is 652.26 cc. and for an 8/1 engine, the TOTAL chamber volume would need to be 93.18cc or less.
If you bore that engine out to 3.95, that makes a swept of 665.68cc, which is an increase of 13.42cc; yeah I did the math three times.
If you then subtract 2cc from the total chamber, making it 91.18, then the compression ratio will climb from 8/1 to 8.3/1
Way more important than this modest increase in compression, would be a Quench reduction to, in the window of .030>.040. Good luck with that.
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Can it be done; Sure. but it would be cheaper to start with a 360.
First; for a 318; yur gonna need custom pistons for open chamber heads, or different custom-design pistons for closed-chamber heads.
Secondly, for a modest street cam, you'd need to modify the pistons to get the Dynamic Compression ratio into a zone that will not detonate on pump gas, or
Third; install water injection to prevent that same detonation.
Whereas;
in a 360LA with KB107s, the pistons will drop in around .012 below deck. Install closed chamber heads with an 028 gasket and the Scr will climb to around 10.7 Install a cam with a typical late closing intake, and the pressure will come in close to 175/180. With alloy heads that will run all day/everyday, on 87E10. Pump it up a lil, to 185/190psi and you got a torque-monster.
Total cost is ;
>with the 318; custom pistons/ custom fitted, closed chamber iron heads to keep the cost down, needs best pump gas or may need water injection. Before long, you'll be wishing you had just dropped in a 360.
>with the 360; off the shelf pistons, alloy heads, runs on skunk-pee, and on the street, you'll never need a bigger engine.
I mean, that's the gist of it.
But I'll tell ya, if I had to stay with a 318, not because of budget restraints, dang rights I'd pump it up! and, I'd run water injection too.
Edited cuz I screwed up the first time.
