hi
I would like to think that my math was correct when calculating the bore of a 390 with additional boring that was done to a short block. I found a short block on craigslist (many out there) and the block looked fine until I measured the bore size. It was more than 4.050 (103.678, if I am correct). My best educated guess was that it was bored once before because the number showed close to 4.08++(with digital ruler). My question - what is allowed or rather recommended bore size or how many time can you bore .30 to a 390 block? Some say .60, others .90. So if the original size is 4.050 if bored once will it put it to 4.080. How does that measure.

Any help is appreciated.
Nick

 

4.05 + .030 = 4.080.

You can probably go .060 if need be. Over that maybe have it sonic checked unless you feel lucky. Always go with as little an overbore as you can.

Your 103.678mm converts to 4.0818, just about right.

You can mic those cylinders up and down and see if there is a barrel shape to them or any other irregularities. If not, you can probably have some 4.080 pistons fitted to them with the proper piston clearance and away you go.

 

I found a 390 block for dirt cheap, but it was bored once. It has little rust all over otherwise great block. Could it be used without boring it again? I thinking 445 stroker. My guess is not but could be wrong.

Nick

 

if you're spending the $$ on the stroker kit don't cheap out on the block , find a stock bore block that you can have bored .030

 

Such a block has to be sonic checked before boring imo. If there is rust in the bores, it is probably deep enough to prevent simple clean up with a hone.

Is this the block that you listed the measurements for?

The 360 and 390 blocks are identical BTW.

 

Yes it is the block I listed the measurements for.

And yes, you are right. Bored .30 block with rust inside the bores would need to be bored again to take rust off. I am not building the racing engine, but having .60 on the block and putting together a 445 stroker is not a bright idea. (but again it was dirt cheap... I mean dirt cheap) Guy was selling 390 block, 390 crank (machined and ready to install), 390 pistons with rods, Edelbrock Performer intake (very clean), 390 heads (d2's) with springs rockers and rods, 390 chain with gears, oil pump, and some other minor engine parts all for $100.
I grabbed everything except the block. Should I have grabbed the block as well?