Have an a12 block sitting in my shed just wondering how far you can bore them or the best way to go about it cheers

3-4mm overbore can be done but check your block out at your local machine shop before going 4mm as some castings may be too thin in some areas to go that far.

We used to get 4mm overbore, to get 1300cc.
I found that about 1 in 5 blocks would take it, you just need to line them all up and get them sonic tested (which aint that expensive)

The cores shift during casting, which leads to them being thinner on one side of the bore...you need to find one that hasn't shifted much....

have heard you can go to 79mm bore, thats 6mm oversize, but you need a custom head gasket for this. 78mm is largest for standard head gasket. I guess it depends on your particular block but this should be quite achievable. I know JTS has an A12 block over 1600cc reliably!

I bored one to 3mm over and used toyota pistons engine was 1270cc..

SLY OLD FOX.....

What clearancing would be needed to fit the a15 crank in? Just the crank or block as well?
I suppose thats whats needed to get 1600cc from an a12 right?
If so it means this particular a12 will need 79mm bores which is amazing.

bump

I'm sceptical of a 79mm bore in an A12 block....77 was the utter limit for me, like I say, it took 5 blocks to find one that would take it...
Someone here (dodgeman perhaps) has put an A14 crank in an A12A block, which is interesting from an engineering point of view, but seems like a lot of work to achieve what an A14 does anyway....

Chris`s a12 stroker is to avoid difficulties with non genuine mounts and engineering into a kb10. I have this problem with the a14 I have in my b10.

Quote:I am using a 1200 block, with an A14 crank that uses A12a rods to move the 77mm A15 pistons up & down.

I am doing this....
Because the A12 block fits the KB10 chassis without mods.
Because it still looks like a 1200 when finished. To the untrained eye, it may even be mistaken for the original A10.
Because the whole thing can be made to appear "factory."
Because it's relatively unique, as i'm sure that very few will duplicate it.
Because i can.

I see 77mm as a practical upper limit & my block is already at 76.5mm, so i guess that i will give it one more try.