Magnum blocks

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Dan the man

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There's a lot mention about the magnum engines being good for a budget build. So I started to do research on them and one issue that arises often is that the magnum blocks should be limited to a maximum over bore of 0.020" because of the block's being a thin wall casting, is this fact or fiction? I thought I read somewhere that the block's have a thin cylinder wall in order to save weight, that little bit of metal isn't going to save that much weight. If I was asked to design a engine I would have it to run as cool with a 0.060" over bore as with a standard bore size.
 
The main advantage is you can find good shape running Magnum fairly easy and they have a bit more cr and the stock magnum head responded well to cam 4bbl and headers. Once you start talking rebuilding the advantages start going away any 360 becomes a good candidate especially if hydraulic roller cam ain't a requirement.

I've heard of the 0.20" overbore limit never heard of anyone having a problem doing the standard 0.30-0.040" overbore.
 
MoPar said the same things about there LA blocks.
A sonic check solves all mysteries.
 
Both Blueprint and ATK stoker motors (long and short blocks) all show being .040” over Magnum block based. I’ve always wondered why they all bore to .040” as a standard instead of the typical .030” I can’t see used Magnum block cores being that bad as to need .040” to clean up. Maybe they get better pricing on the KB or Icon pistons in .040”? I don’t recall ever reading anywhere in their literature that the blocks are sonic checked either. Who really knows what is a magnum blocks overbore limit?
 
Same bore size as a stock 340. That might have something to do with it.
 
12many said:
Both Blueprint and ATK stoker motors (long and short blocks) all show being .040” over Magnum block based. I’ve always wondered why they all bore to .040” as a standard instead of the typical .030” I can’t see used Magnum block cores being that bad as to need .040” to clean up. Maybe they get better pricing on the KB or Icon pistons in .040”? I don’t recall ever reading anywhere in their literature that the blocks are sonic checked either. Who really knows what is a magnum blocks overbore limit?
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Probably cause the odd cylinder might need a 0.040" it's just easier $$$ to use the same kit when you mass produce.
 
I have never sonic checked one but know of a guy that had 2 mags done. He said they
were more consistant and better than the la. The D.C. Bible had a lot of wives tales about thin wall stuff that was debunked by I believe 440 source on big blocks. I do know magnums decks are flat and equal ,front to back and side to side on all the ones I checked. The magnum oil feeds to the mains are also right at 9/32, you won't get nothing out with your bit but I check them anyway.
The 5.9 blocks I have weighed are right at 10lbs heavier than a 360, crank sensor, and 3 to 5 more engine mounting lugs on each side, taller lifter bore casting. I am not sure if the actual bore has more meat or not. I have only seen one 5.9 that needed bored, it had a burned exh valve and must of been driven that way for awhile, most always they are in really good shape for a used engine.
 
Larry Shephard and a few others that wrote in the Mopar books about "Thin Wall" engines were either liars or idiots.
 
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