The most you can bore a 305?

[Carfreak18]

What is the limit on a block of how much you can bore it?..and I still quite dont understand the difference between port n polishing,balancing,and of course boring out the engine....sounds very vague but all the info. would help thanks...

[hotrod_chevyz]

Port and polish is talking about the heads. It helps them flow. When you balance your motor, it means each rod/w piston weighs exactly the same. You can use several different methods in wich to do this. Boring out an engine means your increasing the diameter of the whole where the pistons go. I wouldnt go past .060 bore on any SBC engine. After that throw them away and go find another one. Even at .060 your looking at blowing head gaskets, overheating, or the cylinder getting out of round where its egg shaped. They run real good at .060 tho.

[Carfreak18]

Oh, my friends 305 is bored over .030 and I heard thats about a 310?

[MrPbody]

As said, .060 is considered the practical limit. One could have the block sonic-tested if you wanted to go further. You must have at least .120" left on the "thrust" side of the bore to avoid cylinder "collapse". Cooling systems can be overtaxed by too much boring, as well. 305 has marginal performance potential. The bore simply isn't large enough to let the "good" heads flow like they need too, to make the big power 350 is capable of. We recommend you only bore it far enough to "clean" (the bore is now "fresh"). Little or no power will be gained by boring, until CID is increased significantly. The advantage to boring is it leaves you with a fresh cylinder.

The math to compute CID (cubic inch displacement) is high school geometry.

Pi x R(squared) x H x number of cylinders, where:
Pi = 3.14159
R - bore x .5
H = stroke

There are other methods to compute CID, but this is simple math, regarding the volume of a cylinder, not necessarily tied to an engine. It is the most accurate.

EXAMLE: a 305 has a "standard" bore of 3.75". It has a stroke of 3.48". So...
3.75 x .5 = 1.875
1.875(squared) = 3.516
3.516 x 3.14159 = 11.05 (rounded up, area of the circle)
11.05 x 3.48 = 38.54 (volume of one cylinder)
38.54 x 8 = 307.6 (CID)

It comes out to 307, but Chevy already HAD a production 307, so they rounded down instead of up, and arrived at 305. One can add the amount the block is bored, and using the same formula, arrive at the current displacement.

Helpful?

Jim