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  #1  
Old 03-13-2010, 09:21 PM
Duster_340 Duster_340 is offline
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Default Early 318 Casting Block Same As 340

I have been told by a reliable source, that the early 318LA 1967-1968 were cast from the same mold as the 340's, for a time. This would allow for a 340 bore using the junkyard 318. Does anyone know if this is a fact, and if so, how many years did this go on. I've been told 1967-1968 for sure.
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Old 03-14-2010, 12:21 AM
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pishta pishta is offline
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Its more often heard that the early 360 blocks were based on the same water jacket cores as the 340 so you could get decent overbores in the early 360 blocks, not just the std .040 as published.
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Old 03-14-2010, 12:46 AM
70AARCuda 70AARCuda is offline
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to get a 318 to a 340 that is a .130 bore....

you will need to sonic check the block to get anywhere near that overbore
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Old 03-14-2010, 01:07 AM
fat 360 fat 360 is offline
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It's been done tho,even car craft just did a 4inch bore on a 318.
I'd believe your theory,but yea,sonic check 4 sure!
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Old 03-14-2010, 02:18 AM
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bulldog426 bulldog426 is offline
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i've heard about being able to bore the late 60s blocks as far as .090, and they have a high nickel content, and thick cylinder walls
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Old 03-14-2010, 05:31 AM
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cageman cageman is offline
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Your thinking wrong, the 70 360 block was used on the 340 casting, thats why they share motor mounts, unlike a 340 to 318.
Now being able to bore em standard, Ill find out soon, my uncle just bought a sonic tester, and I have been saving every 67 318 block I have ever came across. I busted a crank out of a rusted up 67 318 last year. I then took a hammer and busted out the cylinder walls, it was the same thickness as my 78 360 block I dropped avalve in, and that was 200 thou thick. Now take 130 thou, divide by two and subtract that from 200 and you are left with 200-65=135, plenty thick. Now this was one cylinder. all it takes is one to be core shifted that it wont work. Thats why I plan on sonic testing them.
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Old 03-14-2010, 05:35 PM
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Ray Bell Ray Bell is offline
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We've had a lot of experience with this sonic testing of 318s...

Poly blocks, admittedly, but the purpose of the LA was to go to thinner wall castings, so I would assume they'd be less of a chance.

Our results?

We went through no fewer than a dozen blocks before we found one we could safely bore to 4.0" without going off-centre. Core shift in all the others, up to 0.140" or so difference between one end of the bank and the other.

Mind you, we're asking for a fairly good block when it's done, so we're probably erring on the side of caution (it's for a race engine). Ben wouldn't have a thrust side wall less than 0.165" at a 4.0" bore. Trust me, however, a lot of them came up with a potential for well under this figure if bored on line.

One cylinder in one block was already down to 0.110" on the thrust side after a 0.030" overbore.

Whether the LAs were much better I couldn't say. Presumably the need to keep things more accurate in the core laying so that thinner castings could result would lead to less core shift. But you're asking for 0.030" greater bore than we were, and as I said, from a block that was ostensibly less 'meaty' to start with.

cageman... you mention that 0.135 is 'plenty thick'... is it really? Could Ben safely go to 4.030" with the block we've found? Minimum wall will be 0.040" at that bore IIRC. In other words, what revs would such thin walls be good for, and what power?

Ben does a lot of race Holden engines and he's sure he loses power to wall flex blowby losses because everyone goes to 0.060" in these.
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Old 03-14-2010, 06:12 PM
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bulldog426 bulldog426 is offline
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think i'd rather just use a 340 block to start with, by time you take the chance of boring the 318 block that much, and spend that money putting them race parts in it, to just blow an engine then thats money gone down the drain, i wouldn't want to take that chance
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