LA blocks

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The 360 in my Dart is bored .070 over, but it is best to sonic test the block to make sure of how far over you can go.
 
63SplitWindow said:
What is the max bore size for a 360 LA block? Would that be the same for a 318 block?
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I would say that you need to get any block sonic checked to be sure.
Usually, most blocks can go 30 thou over bore without any trouble, and any more than that, you are pushing it unless it's sonic checked.
For sure, I wouldn't be buying pistons for anything unless I knew where the block's at for thickness...
 
I've been looking for a source for quite a few years now, of something I read a long time ago. In the late 80's, early 90's there was an article or book about someone sonic checking 318's and boring them .090" over. Might have been Bob Mullen. They were doing that and welding up cranks for a 4" stroke. Obviously much easier nowadays.

Tha answer to your question - is it depends. Most any block can go .030 with no worries. A very rare few blocks have bad core shift and .060 can be a problem. And the opposite is also true, some have perfect cores and you can go .070. A 318 is 3.91 bore, and would need careful checking to go .090" over by someone who knows what they're doing. A 360 is 4" bore. Rumors have persisted for years about early blocks w thicker jackets.
 
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What year of 360 block? You can get some idea if you take out the center core plug and look in between the cylinders The pre 1975 casting date block cylinders nearly touch between cylinders, but I have a 1975 truck casting block that the cylinders touch in as well. Even in the thick blocks, it’s probably still best to sonic test in case of core shift or casting inconsistencies, and I’ve found that running a cell phone bore camera down the coolant holes in the deck to look for pitting beforehand after the block is cleared isn’t a bad idea either.
 
63SplitWindow said:
What is the max bore size for a 360 LA block? Would that be the same for a 318 block?
Click to expand...

the answer to your question is that 99% of the time a 360 is going to have a bigger bore because it starts way bigger
318= 3.91 factory
360= 4 inch factory
huge difference
 
I have my own sonic checker and I Dont even check my LA 360 blocks at .030 over. For personal reasons and how hard I run them at .040 over that’s as long as I will run that block. In my mine it’s lasted 3 plus rebuilds and many years of abuse so I retire it to my scrap pile. If it not damaged I offer it up for free if someone needs it for a milder build but the blocks are tubed so they wouldn’t work on hydraulic cam applications. And no I dont deliver. Lol
 
Years ago the "book" ( How to rebuild your small block Mopar) stated max .040 over bore on LA engines. I do believe after that the sonic testing comes into play. Best to ask a machine shop guy like said it was years ago the book can be wrong my memory can be off etc.
 
63SplitWindow said:
What is the max bore size for a 360 LA block? Would that be the same for a 318 block?
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I would like to point out(not trying to start a pissing match) that a 318 technically cant be bored that big. Its a different casting than a 360 although people will tell you because they look identical in appearance that the 273/318 blocks is the same as 340/360 it really isnt . same with the head castings. An astute student of small block Mopar will learn to go with a 360 or 5.9 magnum. It gives back the most dividend in power in terms of investment than a 318. Simply meaning for the same effort that you would put into a 5.2/ 318 you'll get more back from a 5.9/360
 
B3422w5 said:
the answer to your question is that 99% of the time a 360 is going to have a bigger bore because it starts way bigger
318= 3.91 factory
360= 4 inch factory
huge difference
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My question was more about how big can I go safely with an LA 360 block. I picked up a block that was already machined and prepped for rebuild with a .040 bore.
 
63SplitWindow said:
My question was more about how big can I go safely with an LA 360 block. I picked up a block that was already machined and prepped for rebuild with a .040 bore.
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Until you sonic check it, you won't really know. What do you really get by boring ninety thousandths? Besides a short stroke 360. Ask yourself why a cylinder needs boring out. Valve to block interference? Don't run X heads on a 273. I don't really know if the valve would hit the deck as it opens, I am being deliberately ridiculous to make a point. Pick the right parts and things will work. Does the block need boring to clean up scrapes and rust?
How about just going crazy-stupid, remove the factory cylinder walls, and throw in some super-strong thin wall, large diameter Inconel or some other amazing modern metallurgy sleeves for maximum bore?

Or give the small block the finger and pick up a 400 B block.

Seriously man, a few thousandths won't give you a noticeable difference. What is the percentage difference in displacement? Keep the cylinder walls as thick and RIGID as possible. You will have bigger gains with heads and intake and carb and exhaust tuning. Put your car on a diet too. Put your big block dart on a diet
 
.040" should be fine, but I always sonic-check a block these days.
I had a standard-bore 318 that wouldn't have safely withstood .020" halfway down #2 in the 9 o'clock position. Otherwise, it would've gone .060" easily. A few years ago, one of the Engine Masters Vintage class entries was a Poly 318 that used an LA block (he couldn't find a proper Poly) and the builder claimed .090" was rarely an issue on 318s through '76 or so. Would I do it? No. I agree with the others that have stated keep the walls as thick and rigid as possible. A couple of cubes will not make up for wall flex. The 340 for my Challenger is only .020" over because it was clean there.

If you're hanging around the kind of people that refer to their 350 and 400 Chevrolets as "355" and "406" just because it's been bored .030", find smarter friends (or more confident in their manhood). I've never heard a Mopar guy say he's got a "four-forty six" unless it was immediately followed by "pack". :p A .040"-over 360 is still a 360 to me.
 
63SplitWindow said:
My question was more about how big can I go safely with an LA 360 block. I picked up a block that was already machined and prepped for rebuild with a .040 bore.
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I took your question at face value. Part of it was….is the 360 bore more than a 318. I answered that pretty clearly.
the 360 bore is much bigger.
everyone else already mentioned how big a 360 bore can be before a sonic check was required/ reccomended
 
NoCar340 said:
.040" should be fine, but I always sonic-check a block these days.
I had a standard-bore 318 that wouldn't have safely withstood .020" halfway down #2 in the 9 o'clock position. Otherwise, it would've gone .060" easily. A few years ago, one of the Engine Masters Vintage class entries was a Poly 318 that used an LA block (he couldn't find a proper Poly) and the builder claimed .090" was rarely an issue on 318s through '76 or so. Would I do it? No. I agree with the others that have stated keep the walls as thick and rigid as possible. A couple of cubes will not make up for wall flex. The 340 for my Challenger is only .020" over because it was clean there.

If you're hanging around the kind of people that refer to their 350 and 400 Chevrolets as "355" and "406" just because it's been bored .030", find smarter friends (or more confident in their manhood). I've never heard a Mopar guy say he's got a "four-forty six" unless it was immediately followed by "pack". :p A .040"-over 360 is still a 360 to me.
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I have a .030 over 340 is that a 346? almost a 350 ! LOL! but seriously I agree. Best way I can describe how I see boring is go over just enough to clean up the cylinder. If you keep sharpening a pencil eventually you will have to throw it out and get a new one right? basically don't go over any more than needed save some for later.
 
NoCar340 said:
If you're hanging around the kind of people that refer to their 350 and 400 Chevrolets as "355" and "406" just because it's been bored .030", find smarter friends (or more confident in their manhood). I've never heard a Mopar guy say he's got a "four-forty six" unless it was immediately followed by "pack". :p A .040"-over 360 is still a 360 to me.
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I'm not sure why some guys get so bothered about people stating the actual cubic inches of an engine, after all that's what the factory did. It's not like they "named" a 340 or a 440, they just simply stated the actual cubic inches. With that logic all stroker engines are what the block started out as, and although I know a lot of guys (mostly street racers) that subscribe to that it doesn't go over over well in class racing or when trying to pick the correct camshaft lol. To the op I have built quite a few small blocks .060 over (with no sonic test) with no issues but the only way to know for sure where a block is at is to sonic test it.
 
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On the other hand one could just say "it's a 340 bored .030 over..." which really is more to the point.

The stroker guys are the ones with the oddball cubic inch claims in conversation. Just my $.02
 
"It's just a 360 small block" ; eyeroll

20230108_103703.jpg
 
63SplitWindow said:
What is the max bore size for a 360 LA block? Would that be the same for a 318 block?
Click to expand...
Sonic check it! I had a 340 block that was paper thin, under .030 with a .030 overbore already done to it. Once it’s done, then you know! Plans can be made.

I can’t remember the place, but they are sonic chexking 318 blocks (stock bore at 3.91) and boring them out safely to 4.00 and popping in 4.00 stroke cranks. Yep! That’s right! Safely removing .090 of cylinder wall! YIKES!

There was a time I’d call a person a lier for that statement.
 
The story goes that the early 360 had more cyl wall thickness because the early 360 was a 340 mold with 360 mains?????
What i do know is that my 68 340 block was bored .060 over and my stupid arss shove a intake valve thew the cyl wall.............the hole reviled a paper thin........ok ok maybe .010 to .015 thow thick.
Eng over headed easy
new block bored over 30 and all else the same (Different head, but both 360 heads) and no over heating issue anymore.......coincident?
 
lead69 said:
I'm not sure why some guys get so bothered about people stating the actual cubic inches of an engine, after all that's what the factory did. It's not like they "named" a 340 or a 440, they just simply stated the actual cubic inches. With that logic all stroker engines are what the block started out as, and although I know a lot of guys (mostly street racers) that subscribe to that it doesn't go over over well in class racing or when trying to pick the correct camshaft lol. To the op I have built quite a few small blocks .060 over (with no sonic test) with no issues but the only way to know for sure where a block is at is to sonic test it.
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I had originally written it in my post but must've deleted it at some point: Strokers are a different ball o' wax. That's a sea change in displacement, not five or six measly cubes.
 
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