Technical Max overbore expectation on 60 and 62 389 Pontiac blocks.

Hey all,
I know there is no definitive answer sort of having the bores sonic tested but looking for guesses based upon past experiences. I've got a 1960 4 bolt 389 block and a 1962 replacement 389 SD 4 bolt block. I believe both are .60 over already. Don't see any pitting in the cylinders but they are solid surface rust.. Figuring the 60 block is probably meatier in the cylinders but the 62 block is the main one I'm hoping to be able to go further out without sleeving all 8. Not that custom oversized pistons would be cheap. May start shopping around and dependent upon pricing get the 62 block checked out. 60 block would be secondary concern.but again,dependent upon price have done at a later date. Again,basically looking for general consensus as to whether to get my hopes up or not.

 

.060 OS pistons are all that I see available so that should tell you what the maximum recommended overbore should be.

 

Well,,,,I’m not sure,,,but don’t give up yet .
Abone on here is a big Pontiac guy,,,,he probably has an idea .
Flamedabone is his handle here,,,,pretty sharp guy .

I’m sure it could probably go .070 ,,or .080,,,if need be .
Custom pistons are not cheap,,,but not out of range either,,,,look them up .
Good luck man .

Tommy

 

As far oversized 389 pistons are concerned 400 pontiac pistons will also work starting .030 larger so a .040 or .060 over 400 piston would equal a ,070 or .090 over 389,you just have to make sure they have both sets of valve reliefs so they will work with the earlier heads.

 

You have some rare and desirable blocks there. I would just spend the money to have them sonic checked to know for sure how far you can go. I agree that the ‘60 block seems more likely to take a .070-.090” overbore but you never know, that ‘62 block may still have thick walls.

 

@flamedabone may have some advice.

 

What Bob said (sonic test), is the ONLY way to know how far that you can go with a particular block.

Mike

 

Rather than going for expensive custom pistons, I'd look at getting the cylinders sleeved.

 

Thanks all. Guess I'll make use of some of the down time at work due to the snow and make some calls for some quotes on sonic testing. And probably a few other related services. Been on the fence with whether or not to spend the $$ since I'm not gonna end up using these parts. I'd just rather be able to have an honest ***essment of what they will need to make serviceable again for the next guy. So at least I can say 1 way or another they'll either take another overbore or require sleeves in all cylinders. For run of the mill blocks I'd have coughed twice and p***ed,not even consider shelling out the money to have checked. Been procrastinating long enough,time to get something done.