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.
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?
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.
