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Old 10-02-2012, 03:47 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by ss396si View Post
ive never built an engine before and looking at other options rather than buying a crate motor. If I try my luck at a big block junkyard special. Id be saving money. but its still a risk because its a junkyard motor and i could be throwing my money away. Another option would be buying a short block and putting the heads,rockers etc etc together. First start up is another nail biter..
Not that I'm opposed to junk yard engine's but you really don't know if you have a rebuildable block till it's been stripped, cleaned, and Magnafluxed. That happens before you even put it on the table to check the alignment and dimensions. So by the time you find out; first, is it even a candidate you've put in a fair amount of effort and some cost. Second comes the dimensional inspection where you find out if the bearing bores for the crank and cam are straight or not, whether the cylinder bores are perpendicular to and centered on the crankshaft, and whether the head decks are equadistant from and parallel to the crankshaft also how flat and square they are. And more inspections if youre hunting big power like how centered is the cam, do the lifter bores meet the cam at the correct angle. Etcetera! This leads to what will it cost to correct the imperfections.

So there's a lot to be said for the purchase of a remachined block from the major hot rod catalogs as much, if not all, of this has been done for you and the cost is pretty reasonable as this is what they do en-mass so you save money because they can make specific inspection and remachine set ups that do blocks in quantity at each station.

The good news is that 350-400 horsepower and foot pounds of torque from a 350 is not difficult to acheive. This doesn't tax the engine structure all that much if this is a mostly hot street and occasional strip engine so the vast majority of SBC blocks are up to this. Certainly if you do enough of them you'll hit the exception and maybe the hobby builder will hit one but the odds are way in your favor that statistically you won't hit a bad block either a new GMPP or a remacined from a reputable source.

Going racing is a somewhat different propisition because compared to the street the engine is being used on the high side of its power output all the time, it sees big and sudden changes in power settings and when mounted ahead of a manual transmission has to absorb all the clutch pressure changes as it's engaged and dissengaged buy way of reaction this thrust load out of the crank at the thrust cap and putting it into the block. So racing is a situation that will quickly find marginal strength areas and bust them. Automatics are somewhat gentler in this regard but that depends on how aggressivly they are set up.

An unmolested post 1974 used block should take a .030 to .040 without having to sweat out the wall thickness even for a mild racer but especially for a good hot street motor that isn't being blown or juiced. If going to .060 I do recommend sonic testing as these things are thin wall castings. The pre 1974castings are thicker some of the early blocks like the 283 and some 307s will safely bore .120.

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