Lemonhead wrote:
Thanks Marcus, that is good info on cutting up a block, well done.

I have done 79mm blocks before without a problem, admittedly not boosted.

In my opinion, all of your turbo boost pressure will not be putting high expansion (compression) pressure on the sidewalls of your bore until I'm guessing about the last 25mm (I'm guessin here - ok) of your compression stroke.

All of your ignition and power takes place around here, i.e 25mm down the bore to TDC depending on your set up.

This is a pretty strong area on the A-series block.

So, to sum up my point, go for the 79mm bore, what's the worst that can happen, split a bore? I've never heard of one splitting at the top due to high compression, they have always been mid stroke due to very thin sidewalls, and hey what if you do split one...throw it out and start again.

Nothing ventured nothing gained.