Originally Posted by patsmx5

Meh, it's not a ton. But it's a little. I did the math before. It's somewhere in the engine conversions forum. It's like 1.2% gain in displacement going with a .040 bore IIRC.

Originally Posted by levnubhin

So I guess its just a numbers game? Do I want to spend the extra $100 for a couple of HP?

Originally Posted by patsmx5

Guys .020 or .060 from the cylinder walls is NOT Gonna hurt the cylinder walls. It's a thick *** cast iron clylinder, you will never hurt it. It's the strongest thing in your motor. It's more displacement, which our undersquare engines can use. By increasing the bore .060, you could unshroud the combustion chambers that .060 as well, which helps flow. More flow and more displacement is...... desirable. Do the math but that's surely a few % more displacement. Boring it the minimum is ok so it can be rebuilt again. They do this for commercial equipment, where they would like to get several rebuilds out of the engine for maximum service life.

Sorry Rotornut but reread my post. You were asking stuff I outright already answered.

Originally Posted by patsmx5

Ok, using the factory specs of 3.2678" bore and 3.346" stroke, I get 112.25 cubic inches of displacement.

Let's punch this motor .020 over.
3.2878" bore and 3.346" stroke= 113.63 cubic inches (.000 to .020 displacement changed 1.378 inches)
1.23% more displacement then stock.
1.43 cubic inches larger than stock.


Now let's punch it .040 over
3.3078" bore and 3.346" stroke=115.01 cubic inches (.020 to .040 displacement changed 1.385 inches)
2.46% more displacement then stock.
2.76 cubic inches larger than stock


.060 over
3.3278" bore and 3.346" stroke= 116.35 cubic inches (.040 to .060 displacement changed 1.400)
3.65% more displacement then stock.
4.1 cubic inches larger than stock

Though insignificant, as bore size increases, area increases exponentially. This can be seen as the change in displacement is not the same for each .020 iteration. For example, look at the change in displacement for .020 and .040. The difference between them is 1.385-1.378=.007. However, this is not the case for .040 to .060. Here, the change is .015. Hence it's exponential by a factor of 2. This is because the formula for area is pie times radius squared times height.

An extra 4.1 cubic inches is 3.65% more displacement, or 3.65% more power. However, it will also allow you to unshroud the combustion chambers .060, which will increase flow. I would say the benefits of unshrouding will be greater than the benefit of the larger bore, but at the minimum, equal. If only equal, that's 7.3% increase in power.

That's my inexperience showing. Night night.