318 cylinder limits?
 

Ive decided to take an old presmog 318 for my duster build. I know pretty much exactly what Im going to do to it, but I was curious if any of you know the limits to boring a 318. I know .40 is acceptable, but is going .60 safe?:confused:

I mean bigger is bigger unless its not safe. I noticed that I can get the KB 167's in .60 over and thought "WHY NOT". But figured Ide ask first.

ive seen people bore it 060 over but that is the logical limit for the 318. youd be better off boring 40 and then if you ever do another rebuild you can use the same block.

agreed

watch how much you mill the deck and heads too because youll have to mill the intake as well. whats your choice for an intake and carb?

my honest opinion is that i wouldn't bore it at all unless you had to to get the taper out of the cylinders. if you bore it to .040 or .060 if something happens to mess up and for example a piece of a valve breaks off then its junked, if you don't bore it you don't get 5 extra cid i dont think its worth it but thats just my thoughts

From what I've read, some of the early 318 LA engines from 1967-1969 (and the earlier polysphere engines) can be bored to 4 inches. Careful testing of the cylinder bores with a sonic tester is definitley required and only about 40% (less?) will pass. At sometime in 1969 (supposedley) the castings were modified and the 318 cylinder walls were made thinner. The '69 and later blocks should limited to only a .040 overbore and only .030 from about 1982 and up.

Anyway, I would stay with the .030 oversize pistons. If you want to see how thick your cylinder walls are, your machinist can check them if he has the equipment to do so. Yes this will cost some money, you've got to weigh your options.

I have heard of an early polysphere engine that a guy built that went all the way to 406 cubic inches with a 4 inch crank and 4.020 bore. {torquey!!}

Enjoy!!:D:D

I've always told people to only bore if you have to. If you have to only bore what you have to as well. The more wall you take away, the hotter it can run so you need to make sure that you have a really good cooling system for it. .030 is ok, .040 is my limit (and there has to be a good amount of wall left for that even), and .060 is just too much in my head, but that just me.

the polyshpere can be bored out more than a regular block because the walls were a lot thicker.

Don't be scared little Timmy, .060 over won't make you fall in the well.
hahaha

The 1972 dated 318 block in my Scamp was bored .060 over back in 95 when it was rebuilt, I have had zero issues with it, plus it's guzzled at least 15 bottles of nitrous oxide to boot!

hahaha