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Old 02-13-2020, 04:34 PM
chris slawski chris slawski is offline
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Talking 396 L78 block

Hey folks-
Can a L78 4 bolt block 69 vintage accept an over bore to 4.250 for 427 displacement or will it become unstable?

asking for a friend
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  #2  
Old 02-13-2020, 06:05 PM
dustinm dustinm is offline
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Pull a soft plug and see if you can stick a pencil between the cylinders. I believe this block will be too new and it will fit, but that is the easiest way to see if it is even a candidate.
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Old 02-13-2020, 09:40 PM
JRSully JRSully is offline
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I know the 854 70 L78 blocks can take a big bore job, they are actually 30 over 396's (402) from the factory
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Old 02-13-2020, 10:20 PM
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The cylinders are going to be awful thin if you do.
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Old 02-13-2020, 10:31 PM
Salvatore Salvatore is offline
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If you are looking for performance not sure the 427 has much over the L78 configuration to risk that bore.
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Old 02-13-2020, 11:52 PM
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A 69 big block of any C.U. Or horse is worth more with as little overbore as can be done to clean up the block, imo. A heavy overbore diminishes any 396 or 427. With so many gen.4 454 blocks available, there is no need or reason to bore a 396 out that much, if it can even safely be done.
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Old 02-14-2020, 01:05 AM
wvhylander wvhylander is offline
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Bore it .060 buy a set of UEM Pistons($650) and a Scat 4" stroker crank and you have a 434ci. motor. Step up to Ross pistons ($1100) and a 4.25 stroke crank you have a 461ci. from a 396 block.
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Old 02-14-2020, 05:43 PM
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As JRSully said,if the block is one of the late 1969 production & really a 402cid,you should be fine.
Easiest way to identify one is if it has a 3 letter Suffix code on the machined pad beginning with the letter "C"...example CJD or CKF,as opposed to just JD or KF.
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Old 02-15-2020, 03:45 PM
L78steve L78steve is offline
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The early 65 Fang 396 block has lots of meat also.
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Old 02-15-2020, 05:13 PM
plumL78 plumL78 is offline
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I have a 65 396 punched to a 427 bore. we used hard block to stabilize the cyls. been in my car for many years but its an early block
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