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How big can you comfortably bore a LA 360 Block? #2010085
02/11/16 08:35 PM
02/11/16 08:35 PM
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Graham, WA
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Polarapete Offline OP
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I have been storing some engine cores that I have acquired in the "dirty side" of my shop and yesterday I finally opened up the LA 360 truck motor that I have had for a couple of years. I was told it was rebuilt and it has to be because at least one of the pistons is marked .040. The bores are smooth with almost no ridge with the exception of one and there is some pitting in the top of that bore about 1.5" down, so I am guessing it may require a bore but I may be able to get by with honing, particularly if I go with a forged piston.

The object of this exercise is replace the existing LA 318 in my daily driver with a fresh engine and more power. I also have a LA 318 pass core that I know is original and I could use that block with the "974" 360 cylinder heads if they are not cracked for better breathing.

I did the same kind of a swap years ago in a '74 D 100 with a 360, a new truck pan and a B&M flex plate so it is nothing new, but that motor was a virgin and I put .030 cast pistons in it.


1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction
1998 Ram 2500 QuadCab, new daily driver.
2008 Honda Element
2014 Carry-On 7x14 Cargo Trailer
Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010203
02/11/16 11:21 PM
02/11/16 11:21 PM
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Lincoln Nebraska
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RapidRobert Offline
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If I was boring to 60 I'd likely be on the safe side & sonic check it esp as you are going to subject it to some spirited driving. If just honing out for forged I'd likely go as is (if it will clean up).


live every 24 hour block of time like it's your last day on earth
Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010258
02/12/16 12:44 AM
02/12/16 12:44 AM
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MI, usa
dvw Offline
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The 360 block out of my 76 Volare has been .060" over for 20 years. Makes around 450hp.
Doug

Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010584
02/12/16 05:49 PM
02/12/16 05:49 PM
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Paul_Fancsali Offline
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Early 360s can go 60 over easy most new can too. Myself if the pits are not too bad I would bottle hone the block and put it together with new rings Bad if you can catch finger nail in pitt

Re: How big can you comfortably bore a LA 360 Block? [Re: Paul_Fancsali] #2010603
02/12/16 06:13 PM
02/12/16 06:13 PM
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Graham, WA
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Polarapete Offline OP
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I have been doing some reading in the Mopar Engine bible for another issue and found that the '76 and earlier 360 can be bored to .060 as they used the 340 casting molds, but the '77 and later 360s used a lighter weight casting. So I may be good to go with this block and because it came with the truck pan it was a good buy at $100.00 for the long block. Now I just hope the "974" heads are salvageable...or I will turn in my winning $5.00 Mega Millions ticket for another winner and go nuts on this build.


1986 Dodge Ramcharger 440 2wd, Bracket Racer Under Construction
1998 Ram 2500 QuadCab, new daily driver.
2008 Honda Element
2014 Carry-On 7x14 Cargo Trailer
Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010814
02/12/16 10:57 PM
02/12/16 10:57 PM
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Florida
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mopar346 Offline
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If the pistons are good, fine another block. bore it 40 over and have at it. Block and bore cheaper than bore and pistons. twocents


Careful, your character's showing!
Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010878
02/13/16 12:47 AM
02/13/16 12:47 AM
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Lake Orion, MI
goldduster318 Offline
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Lake Orion, MI
The motor I used to have in my Duster was a 360 that was bored +0.040 over already and had some wear.

I was picking up my 340 from Mike at MRL Performance and casually mentioned that I thought my old block was just a scrap heap junker being a 1977 model block and being +0.040" already.

He didn't seem phased so after I pulled it, he bought the block from me. Turns out after sonic checking it was plenty thick to go 0.060" over so they did so and the engine made 420hp. So get it sonic checked.


'70 Duster 470hp 340/T56 Magnum/8 3/4 3.23 Sure-Grip
Re: How big can you comfortably bore a LA 360 Block? [Re: goldduster318] #2010904
02/13/16 01:54 AM
02/13/16 01:54 AM
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Granite Bay CA
Kern Dog Offline
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Granite Bay CA
Mopar Action magazine did an article on this several years ago. My memory isn't 100% accurate on the details but this is what I do recall:

The 1971 360 2 barrel engines were cast using 340 core molds. This is why the 360 uses the same motor mount lugs on the block as the 340s do. The 340 had a 4.040 bore size and if core shift was minimal, those 340s could have gone .060 over to a 4.10 number. Since the 360 was shipped with a bore size of 4.00, it stands to reason that a 1971 360 could possibly be bored out to 4.10 of the walls show no thin spots during sonic checking. The article clearly restated the mantra of the magazine that it isn't big inch engines that make power, it is solid cylinder walls that do not flex or distort during operation. The few HP from boring an engine to the limits can be lost if the pistons and rings don't seal well.

Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2010952
02/13/16 04:41 AM
02/13/16 04:41 AM
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Leucadia, Ca.
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vdriver Offline
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FWIW:

DSCN4025.JPGDSCN4024.JPG
Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2011396
02/13/16 10:33 PM
02/13/16 10:33 PM
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Georgetown de usa
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Eggman Offline
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Georgetown de usa
my 86 block is .060

Re: How big can you comfortably bore a LA 360 Block? [Re: Polarapete] #2012453
02/15/16 02:50 PM
02/15/16 02:50 PM
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Columbia, CT
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moper Offline
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Columbia, CT
The books don't take into account the cruddy casting that was done and for the most part those are myths that have been debunked over time. Core shift which can limit the bore thickness ALL blocks should be sonic tested if you are going to non-factory strokes or they are going beyond .030 over. It would stink to have the work done and have a problem with your result because you failed to drop the extra coin on a sonic test. If you had one at .040, I'd either not sweat the pits, ridge ream it, and run it or get another one that's std bore. They are very plentiful and fairly cheap - even in Magnum form where you can use the roller cams in them.


Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.






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