390 x 2. Which block? Sonics attached.

[66FAIRLANE]

I have just sonic tested my two spare 390 blocks. One is STD one is .030 already. I have usable F2291 pistons at .030 & .040.

I was liking the look of my 030 block to go another 10 thou until I saw the thin spot at the bottom of number 7. Double, triple, quadruple checked. Its there. Not very big, maybe 1/8" or less but its there. It moves right back up to 120 all around it.

Apart from this are either of these blocks known for any strengths or weaknesses? Oil feed to the deck issues etc?

Any opinions on which one to use?

[jayb]

No reason you couldn't sleeve #7 if you are concerned.  That thin spot is not on a thrust side, and it is at the bottom of the bore, so you might be able to get away with using it as is.  However, putting a sleeve in it would give you some peace of mind.  Don't be afraid to sleeve...

[66FAIRLANE]

I was just having a think (dangerous I know). It is literally right down the bottom. How would an inch of hardblock affect a street motor?

[GJCAT427]

I was thinking that yesterday when I first read your post. It shouldn`t hurt anything as the main heat would be in the upper part of the cylinder bore.

[jayb]

Agree with Garry, an inch of hard block would cause no issues in a street car.  That would be a good solution.