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  #1  
Old 11-19-2010, 01:58 PM
daryl2399 daryl2399 is offline
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Default 360 La blocks

Planning a new build. Probably about 14 to 1 on the compression. What year blocks have the thickest walls? Will a stock block hold this?
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Old 11-19-2010, 02:16 PM
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JVMopar JVMopar is offline
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If I remember right the stock block will hold 500-600 hp before it splits the cylinder walls open. I'm thinking it was closer to the 500 hp but don't remember exactly what the article said.
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Old 11-19-2010, 04:21 PM
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I have a 70 360 block and a 78 360 block, they both sonic tested the same.
Better order up some cometic head gaskets with compression like that
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Old 11-20-2010, 03:59 PM
daryl2399 daryl2399 is offline
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WAS going to have it sonic checked just thought some of the earlyer blocks might have thicker walls. Got 3 or 4 to chose from here. Plan on running w2 heads. ran them on a stroked 340 with that kind of compression without a problem
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Old 11-21-2010, 09:11 PM
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my dad has a cuda with a magnum 360 on alcohol and it has like 13.5
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Old 11-21-2010, 10:49 PM
daryl2399 daryl2399 is offline
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Wow Have heard the walls on the magiums are not near us thick as the old LA blocks
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Old 11-22-2010, 12:06 AM
moparracer moparracer is offline
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I personally had a 360 with 13.5:1 compression in a dirt tracker. I used Fel-Pro blue head gaskets with head studs, and had no problems at all.
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Old 11-22-2010, 12:10 PM
daryl2399 daryl2399 is offline
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Ran alot of high compression engines with out problems unless u get them hot. Always use arp studs. Thinking bout a 4.04 bore which would make it a 368. Have also heard that the early blocks have thicker walls. Anyone no for sure?
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Old 11-22-2010, 04:28 PM
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Very early 360's used the 340 water jacket castings, but I would trust cageman as he has hard numbers saying they are the same. I would use the later block as they made revisions throughout the years, usually for the better, but the theory of core shift with higher casting numbers has pretty much been debunked on 440source.com testing.
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Old 11-23-2010, 02:45 AM
DartGT66 DartGT66 is offline
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Copied from Shady Dell speed shops page, they hava a lot of experience with SB mopars and it's pretty much the only engine type they build:

How far can I safely bore my block?

I'm often stumped why people ask this question, because unless I have ESP or some other psychic ability, I can not answer this question definitively. SONIC testing is the only definitive way to know what your specific blocks cylinder walls look like thickness wise. HOWEVER, I will give you some generalities, just because so many people want to know. Do not take the following as gospel - only the sonic tester knows for sure.

318 blocks don't like large bores PERIOD. .030" over is about the maximum I will go before sonic testing a 318 block.
340 blocks: any year, 1967-1973, 4.04" is stock bore, and .030" over is generally very safe. .040" over I would have no qualms generally doing. Going .060" over to a 4.10" bore on a factory 340 block IMO is pushing it, and I would only do this knowing my sonic #s. Largest known running 340 block that I know of is at 4.125" bore.
360 blocks: and here we get into certain years being felt to be better than others. Generally yes, any 360 block up until 1974ish is considered a little better block. And the above rules for a 340 apply. 1975 and later, I will go .040" over with no qualms. I have also seen many blocks from the late 70s go 4.07" or more and be used as successful race blocks for many years. However, I'd sonic test the newer stuff if going much over .040".
X block, R block, R1, R1As: These are all non Siamese bore. MP recommends a max overbore of 4.08" on these blocks, however most people find that this is erring on the side of caution. Many of these blocks can go 4.10", 4.125" or even larger bore on occasion. My personal feeling is anything over 4.10" on these and we sonic test. Up to 4.10" I would not generally do it. Largest running non Siamese bore X, R, R1, R1A, or R2 I know of would be 4.155"
Non Siamese R2/R3s, the above rules apply. Largest running non Siamese bore R3 I know of, is at 4.165"
Siamese Bore R2/R3 race blocks: 4.180" is a common bore size to run on these blocks, and many will run 4.22" as well. I personally would run up to 4.22" without sonic testing. Over 4.22" and I would sonic test. Largest bore running R3 engine that I personally know of, is at 4.25" bore.
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  #11  
Old 11-23-2010, 05:24 AM
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Ray Bell Ray Bell is offline
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I wouldn't have expected any change much in wall thickness from the time the 360s first arrived...

The move toward 'thinwall' castings was a thing of the early sixties (most outstanding being the 221 Ford V8) and all that development, I would have thought, would have been completed by 1970 or so.
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Old 11-23-2010, 01:48 PM
daryl2399 daryl2399 is offline
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Thanks guys learned something today. First block I looked at here the numbers say its 71 to 74. Probably take it down an have it sonic checkrd tomorrow
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