Has anyone ever turned the block upside down and grouted only the upper part of the cylinders ? Maybe 1 or 2 inches ?

You would have to use a block deck plate, then when finished drill through the grout for the coolant openings.

Why distort the cylinder walls now?
When you say "Grout" what brand and type are you thinking of using?
I won't consider using any block filler due to the different temperature of the cylinder walls were there is "grout or cement filler" versus where there is coolant
With the better market now on new thicker race blocks why not start with a better block instead of trying to patch up an old stock block

That’s the LAST place you want block filler. That’s where most of the heat is dumped from the piston though the rings. I think that’s a really bad idea.

I would not want the top half of my bores to be that much hotter than the lower half.

I'm going to assume you have a block that has been heavily decked. Aftermarket blocks have very thick decks like you're trying to achieve, but they can get away with it because of cast iron's ability to transfer heat. Your typical block filler works much better as an insulator for heat transfer rather than a conductor. If you were trying to save a hemi block or something, maaaybe you could get away with molten aluminum poured in since it would be a little better for heat transfer, but I'd only want to try it on block that would be junk otherwise.

Disclaimer: I'm no expert, just speculating.

Not directly related to your question but...

If I remember correctly is the past we managed to split cylinder walls on stock small blocks that were grouted, one a half fill the other a full fill.

These were very high compression engines, I think one was 16-1 the other 15-1.

No problems with R blocks.

I would believe it I sleeved a small block at 4.28 outside and there was pin holes

I'm not planning on doing this grout work with any block I have. No current need.

I was just thinking. I have read that sometimes the cylinder walls will sonic-check thin up at the top, which is where the pressure is highest.

True, it's also where you need cooling the most.

I have no experience with the stuff, I don't know how rigid, or strength-enhancing, it really is.

I agree, a true heavy duty block would be much preferable.

You can't drill the cooling passages out from the water pump openings, you'll run right into #1/#2 cylinder. I know because we overfilled a block and I tried everything from acid to drilling it out. Lesson learned, make sure the guy watching the pour has his glasses on cause once it's in there it ain't coming out.

A39, I never thought of that !

If I were going to do that, I would fill the whole thing. Not advisable for a gasoline powered, bracket application. I've filled them to the bottom of the water pump holes in the past.

It's a bandaid. Something else is going to move or break at some point. We're just trying to keep the cylinders round.

As a39 Coronet said you can't redrill it in that way. and if you do fill it conventionally TOO HIGH, you'll block coolant flow thru the block at the blind headbolt bosses. Maybe that is what's been conveyed and understood in his reply?