Over boring a 330FT block

[bsprowl]

The following is based on a 15/64 drill bit test on 330 FT block:                       
4.63 bore spacing.  Subtract the drill bit diameter, 0.219, leaves 4.411 inches.                     
Allowing (subtracting) for two 1/8th inch (0.125”) cylinder walls leaves 4.161.                       
This is just over a 0.030 over bored 428 cylinder.  The 428 has a 4.13 bore; with a 0.030 over bore the bore is 4.16.                       
So if there isn’t much core shift I should be able to bore this block to use 428 pistons.                     

Or am I mssing something?

[blykins]

Bob, I wouldn't even take time to mess with drill bits.  Find a local machinist/engine builder with a sonic tester and have it tested, and even then, keep your fingers crossed.

You can't see all the places behind the cylinders where it can be thin/pitted.

In addition, the cylinder wall thickness is paramount to ring seal.  You're better off with a thicker cylinder wall than a thinner one.

[bsprowl]

I agree about the thicker wall.  And the sonic check before boring.

I thought and 1/8th inch wall would be more than enough.  Probably use a 4.13 bore so it could be overbored later.

[frnkeore]

I have a late 330 block, with side ribs. I did the same test and found that there was a fairly big difference, between the top of the cylinder and the bottom.

The bottom (from memory of 3 years ago) was 3/16, while the top, under the deck, was 9/32. Also, my block doesn't have the third rib in the skirt.

[bsprowl]

My block is dated Jan 16 1970 and doesn't have the ribs. 

The drill bit barely goes in near the center and won't move up and down more than an inch. 

It has the reinforced mains.

[frnkeore]

As I remember, my block is a '72. I think they started the ribs close to '71.

With good sonic map readings, you should be good to at least 4.13.