Bore the 655 348 block to 409 ?

[oldskydog]

Maybe this is common knowledge but I believe there is a quick (not scientific) way to tell if you can safely bore the 655 348 block to 409 specs as has been rumored.

In early 66 Corvette production there were a few documented 427 blocks with a 961 (396) casting number instead of the 942. Apparently some early blocks were cast with the 427 cylinder wall cores before the casting nujmber was changed and the quick way to tell if a 961 block had the thicker walls was to remove the center freeze plug on the side of the block and try to insert a pencil between the cylinder walls in the water jacket. If the pencil would go then it was a 396 core and couldn't be bored to 427. If the pencil wouldn't fit then it had the 427 core.

It occurred to me that the same test might apply to the 655 348 block. Since I don't have a 655 I can't do the test but one of you guys that have 655's can. I checked my 962 (63 cast) 348 and the pencil went easily between the walls. I checked my 61 409 block and the pencil would not fit between the walls.

I realize that the only way to tell for sure is to have it sonic checked but this might give a quick indication if it might be feaseable.

 

[1958 delivery]

All the early (1965) four bolt 396 blocks (961 cast) were cast with thick walls that would usually bore safely to 4.25".

 

[chevymusclecars]

The 961 block is a two bolt main, the 962 is a four bolt main.

Bill

 

[1958 delivery]

The 961 block is a two bolt main, the 962 is a four bolt main.

Bill

You're right about the 962. The 961 came in both 2 and 4 bolt configurations. Every 1965 396 4-bolt I've seen was of the thick wall variety. But this has nothing to do with 409's!

What was that 655 348 out of, 1965 trucks?

 

[jim_ss409]

That's an interesting idea. Hopefully someone with a 355 block will check it out.

 

[boxerdog]

sonic check 655

One of the W's I am working on is a 655 block, I believe from a 1965 truck or piece of farm equipment; we sonic checked it and it would have easily gone to 409 bore. I think Aubrey talked me out of it, said "save it for the next guy" or something to that effect.

So it is going .060 with a 427 crank and 6.385 rods. It is a really neat block with much heavier main webs, etc than a normal 348.

I wish I had another one, but shipping iron all over the country gets pricey.

 

[djohnson1937]

I tried this test on my 655 block (replacement truck block) and was able to fit a pencil between the walls.

Does anybody have a bigger pencil?

 

[Impalaguru]

I had a 655 that was bored to std 409. It ran well for me. It was in a car I sold almost 5 years ago. I assume it's still running OK. The person I bought the engine from did have the block checked first. Not sure if I would ever do it myself, though. At the time it was an affordable way for a 20 year old kid to get a w-motor.
Ross