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Sixties or seventies ?

budascuda

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Hi folks,
Could someone please tell me if a 1968 340 block is compatible or as good as a 1970 340 block?
Thanks in advance.
 

340challconvert

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Looking at a 340 block, be aware if the block is standard bore, or has been bored. General consensus is a 60 " bore is the max. Sonic check any a block u are considering. Street use, the engine should be ok with a 60" bore or less. People have bored them out to 80" w/o trouble but I would avoid them.
Just my thoughts!
 

budascuda

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Looking at a 340 block, be aware if the block is standard bore, or has been bored. General consensus is a 60 " bore is the max. Sonic check any a block u are considering. Street use, the engine should be ok with a 60" bore or less. People have bored them out to 80" w/o trouble but I would avoid them.
Just my thoughts!

Thanks Paharamia, I didn't know you could have 80" over bore on a 340, but I too would pass on 80" over.
The owner says it's 30" over and just recently back from machine shop. However, I did forget to ask if the shop did a Sonic test. that is a very very good point. I just took for granted the fact that the shop could have machined the block without checking for cracks in it, Just the thought, gives me the chills! Thanks for the heads up.
 

aussiemark

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All 340 blocks are equally good they just went cheap with the cast cranks and small valves in the latter engines, the T/A blocks are thicker around the pan rails for 4 bolt main conversions so they are the best production car block then you had the X block of the late 70's this was the best block of all.
 

budascuda

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All 340 blocks are equally good they just went cheap with the cast cranks and small valves in the latter engines, the T/A blocks are thicker around the pan rails for 4 bolt main conversions so they are the best production car block then you had the X block of the late 70's this was the best block of all.

Very interesting, I thought "high performance" was a thing of the past by the late seventies. what engine had the X block ?
 

budascuda

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I just found this on one of the chat sites;
The "X" block was produced in the late 70s as a race block. The features/differences from a stock block are:

They were standard deck height, accepted all standard components and could be interchanged with a stock block.

The are high nickel content, have added material around the main webs, oil pan rails, block deck, front of the block and thicker cylinder walls. This is to prevent(or reduce) block flex under high HP/torque loads. The blocks weigh about 225 lbs. but can be severly lightened to about 172-174 lbs. Standard bore size was 3.910". The blocks actually have 318 markings on the size but have a large "X" on the right front of the block.

They came with both 2 bolt and 4 bolt mains. All can be machined for 4 bolt mains.

They can be decked down to 9.200" but most stopped at 9.300".

They can be bored to 4.100" for oval track, 4.125" for drag use. These are very safe bores.

They have provisions for front oiling(in addition to standard rear oiling). Most serious engines oil from both ends.

They are excellent blocks, better quality than the "R" series, and I would rather have an "X" than the equivalent "R1" with 59 degree lifter bores. And, they have aged naturally rather than the chemical aging used on the "R".
 

aussiemark

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The more recent ones were P5153743 and P5153478AB both Siamese and P5007552 AB full water jacket all have 4 bolt mains on the 3 middle tunnels not sure if they are around anymore but if I was going to spend this much on a block I would put a bit more in and get a 2nd gen Hemi block.
 

budascuda

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Hey aussiemark, what is this "naturally aging" a block?
 

aussiemark

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Natural aging is when the block is put aside for a long period of time sometimes outside in the elements until the casting stabilises normally a new casing will keep moving around for some time after it is made so if it is precision machined the measurements and geometry will change until the casting stabilises. This is the reason a lot of engine builders choose a used (seasoned) block instead of a new one this way the casting has finished moving around and is seasoned so it will hold it's shape and any machining done will stay the same after repeated heat cycles and thrashings.
 

budascuda

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So is it necessary to line bore the crank tunnels ?
 
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aussiemark

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A lot of people do it for no reason you only need to line bore if the tunnels are not straight, or you have to fit new or not original caps to the block for what every reason. The easiest way to check is get your crank checked for straight and machined if needed then install the crank into the block with new bearings and the correct clearance if the crank turns nice and free you are good to go and line boring is not needed. The more times a block is line bored the closer the crank will get to the cam and the timing chain will get slack you can get special shorter timing chains but if you don't need to do it it's better not to.
 
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