Building 340 short block

Vs29H1B said
Really need to think about these questions and ask yourself what your usage and purpose intended for this build. Using sleeves may be your best bet if you are only thinking about building the 340, as opposed to the 360 roller build suggestions?

Also are you aware that the max overbore limit for a 340 block - according to the factory service manual specs - is .040 overbore? Going further with overboring increases your chances of overheating, among other things?

The max bore of the block should be determined by the cylinder wall thickness. NOT what the book will say. The past limits were printed for a reason and so is the current thinking and working measures of going beyond the past printed limits.

Overall, it will depend on power level sought by the builders wants.

1970Duster said
If its for the street, no way I'd fill the block.
Why not just sleeve the cylinders? Or use a different block. All that said I know it been said before, why not use an LA 360 roller block? You'd be miles ahead with a roller and 360s are easy to find plus cheaper.

Sleeveing the cylinder or cyclinders can be expensive over a cheaper block filling. Cooling will never improve with this method but it is not impossible to have a high HP engine running well in the street with half a block filled. Improvements in the cooling system maybe needed.

To the OE poster, what kind of power are you seeking?

The hyper-U slugs are fine for a lot of builds. $1200 is way to much for slugs. As said above, you can have a 1 off custom set of forged slugs made cheaper.