Overbore and intake valve size

[House of Darts]

'79 AMC 304/2 125/180- is there any advantage to boring .060 with a small(1.79) intake and 2BBL carb or will a .030 overbore be sufficient??

[Bob Mulry]

Well,

Just looking at an engine as an air pump.....

With a +.030 overbore the displacement is 308 ci

With a +.060 overbore the displacement is 314 ci

With a +.080 overbore the displacement is 318 ci

If you make 1 hp/ci you would gain 6 hp going to +.060 plus the additional compression.....

Just my thoughts,

PS:
Don't forget to stroke the crankshaft for additional displacement and compression
With a +.060 bore and a .013 stroke you end up with 315 ci

[junior barns]

Is there any affect of over boring if the intake cant flow any more air?

[Bob Mulry]

Originally Posted by junior barns

Is there any affect of over boring if the intake cant flow any more air?

Most likely.....

But shouldn't you build your combination around what you run and more cubic inches can't be a bad thing???????

[junior barns]

yes most definitely,it was just a thought. If you went from 030 to 060 and car slowed down with no other changes could intake actually slow it down in this case?

[SSDiv6]

In addition to more cubic inches, it will unshroud the valves and chamber which it is a plus for engine flow.

[House of Darts]

Thinking out loud....the extra weight of the piston is of any concern? The cylinder fills to capacity regardless of any restrictions(valve size, head design)?

[Mark Yacavone]

Originally Posted by House of Darts

Thinking out loud....the extra weight of the piston is of any concern? The cylinder fills to capacity regardless of any restrictions(valve size, head design)?

The piston has a spec weight, regardless of over- bore size.
Everything helps on a small motor, but make sure you concentrate on minimizing the deck height.

[jmantle]

Originally Posted by House of Darts

'79 AMC 304/2 125/180- is there any advantage to boring .060 with a small(1.79) intake and 2BBL carb or will a .030 overbore be sufficient??

If you are having pistons made, first make sure you can get rings for the bore size you pick. Any bore size up to .080 over is legal even if its metric.

Jim Mantle V/SA 6632