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post #1 of (permalink) Old 04-17-2000, 04:09 PM
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convert 345 to 392

I was wondering, since most of the parts from a 345 are the same as the 392, and since you can even put 345 heads on a 392, is it possable to do a full convertion to the 392. Do you need to just bore it out or do you need the 392 crank as well.

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post #2 of (permalink) Old 06-13-2000, 10:51 PM
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Re: convert 345 to 392

The 392 block is different. The 345 heads only fit the early 392's. The 392E is an extra cooling block and the only heads that will fit are the 392E heads. The cranks are the same for the 304,345 and 392 as are the stock cams. The best solution is to find an early 392 put 345 heads on it. This will net you about 10:1 compression. Snyder and Comp Cams both make several good cams for these engines. Good luck! P.S. the 392 drops right in where the 345 used to be.

post #3 of (permalink) Old 06-14-2000, 12:13 AM
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Re: convert 345 to 392

I thought the 392 had a different crank and a longer stroke than the 345, but on earlier ones was almost identical.... correct me if im wrong... I also thought a 345 to 392 conversion had been done before by others... I am mostly familiar with the 345, so I may be wrong, its just what I recall from previous discussion in chat and on IHC digest...


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post #4 of (permalink) Old 06-14-2000, 12:43 AM
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Re: convert 345 to 392

The 345 and 392 have the same stroke ( 3 21/32 ), I don't know if the cranks are the same. The 304 has a
different stroke ( 3 7/32 ), so the 304 crank is different than the others. I've never heard of anyone successfully
converting a 345 to a 392.

Later,
Curt

post #5 of (permalink) Old 06-20-2000, 12:03 AM
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Re: convert 345 to 392

I stand corrected. The 304 crank is different.

post #6 of (permalink) Old 06-20-2000, 05:23 PM
 
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Re: convert 345 to 392

My understanding is the 345 and 392 cranks *are* different, but not by much.

Mostly it's a counter-balance thing since the 392 used 1/4" larger pistons which would naturally weigh more. You can use a 345 crank with a 392 (or vice versa) if you're having everything balanced during a rebuild.

My recently built 345 in my daily driver/trail rig sports a 345 crank, 392 rods, 392 (welded style) rocker arms, 345 (boat style) rocker shaft, 392 pushrods. 345's 2bbl intake and heads.. soon a different 345's modified 2bbl TBI intake and a ProJection.

To turn a 345 into a 392, you'd need to have the engine overbored .250 of an inch. Typically you can't buy anything larger than a .060 piston because the cylinder walls are too thin.

The block castings ARE different between the 345 and 392. If you DID punch a 345 .250 over and didn't run into a water jacket, you will certainly have sacrificed longevity and reliability for 47 cid.

Now, you could definitely take your current 345, and buy just a non-IC 392 *BLOCK*.. buy new pistons, and reuse the 345 crank, rods, heads, rockers, pushrods, etc. That is, if you have the later 345.

There was a change in the very early 70s. There WERE two rods used - a lighter rod for the 345, and a heavier rod for the 392. IH switched to a single common connecting rod for both the 345 and the 392 very early in the 70s (Eldon has posted the exact details on the Binder Bulletin FAQ). Thus, a later (definitely, say, a '77 345) 345's connecting rods should be up to serving in a 392.

Just after I had bought the pistons and they were being fitted to my 345 block, I was at the junkyard looking for a wide T19 when I found a 392.. it wasn't until a little after I realized I should have sent the 345 pistons back, bought the 392 block, and bought 392 pistons and had the 47cid for "free" - or just the price of a bare block and some extra cleaning.

Whoops.

-Tom

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