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When looking for a 350 block for a 383 build are there any casting codes that are preferred? Are there any that you want to stay away from? I tried to go through as many of the 383 questions on this forum but I didn't really see this question. Most of them are about a block someone already has. I have found a few articles that said a one piece seal is preferred but it didn't really go into why.
 

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Rod...from a Chrysler?
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The one piece seal blocks usually have the bosses in the camshaft valley for factory style roller rocker set up. Aftermarket roller cams are expensive.
And of course, I've nver had my one piece main seal engine leak, but I have had every 2 piece seal on any SBC I've owned, leak.
Also look for 4 bolt main blocks.
 

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Hold out for a one-piece main seal block. Unless you want to use a flat tappet cam or electric fuel pump, make sure the block is machined for mechanical fuel pump, roller lifter "spiders" and cam retainer plate. Not all of them were. I have had very good luck with 880 castings. One was at least 15 years old and the bores cleaned up before +.010". The other was very old and nasty, but cleaned up before +.030". Neither needed to be line bored/honed.
 

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There are variations on the one piece seal blocks at the coolant pump mount where the old time pump bypass may or not be finished. Not a major item but something to check to be sure the selected coolant pump and block will not leak at this point if one or the other has the provision and the other not.

Pre 1996 blocks use the old time timing case cover so the right locating pins and faster er holes are there. 96 and newer production blocks used a plastic timing cover which while retaining the general pin and fastener pattern does not use the same combination so you may find it necessary to perform drilling and tapping operations which you certainly want to do before starting assembly, so check this out ahead of time.

You will find that starting with 95 blocks there is more space in the crankcase which reduces or eliminates clearance given along the pan rails, roof of crankcase and cylinder spigots where they extend the bore wall into the crankcase. Again this needs to be checkout early.

You will find that cap bolt rods provide more crankcase clearance than bolt and nut configured rods. This greatly reduces, if not eliminates, needed clearance grinding on the crankcase or on the rod for cam clearance. Again this needs to be checked out but generally the cap bolt style rod is much less an issue to obtain clearances.

For rods the 6 inch and its matching piston makes for a simpler balance situation. These even with a cast crank most often will internally balance a 383 allowing the use of standard one piece rear seal 350 flywheel or flexplate as the transmission type demands and a standard 350 damper. Getting into the shorter rods of 5.7 or the 400 rod of 5.565 inch length and their matching pistons usually require external balance using balance modification for the 350 flywheel or flexplate and the use of a 400 damper. So this is another up front decision as to direction to go in. As a general a daily driver street performance operated under 5600 RPM external balance is OK. However, for engines that get wound out frequently internal balance is easier on the bearings and crankshaft.

Aluminum head’s are another up front decision. This is an issue of piston crown to head deck clearance and its affect on squish/quench and potentially compression ratio. Here the standard GM spec of .025 inch from piston crown edge at TDC to the deck can be a problem with gasket selection which gets into a dimensional stack up that is thicker than the desired .035 to .045 inch of squish quench clearance. Aluminum head’s due their greater amount of thermal expansion than the cast iron block and steel faced gaskets ride better on a composite or MLS gasket such that the differential expansion rate is mostly absorbed in the layers of the gasket. But these gaskets tend to be rather thick the thinnest over the counter being .028 which added with the standard crown to deck of .025 clearance amounts to .053 inch. As this clearance gets wider cylinder turbulence reduces which enhances the likelihood of detonation occurring and generally reduces burn efficiency which reduces power output and increases fuel consumption. This doesn’t necessarily make for a bad engine, but certainly reduces advantages that can be had with attention to the details. Now FelPro makes a coated .015 thick shim gasket that nets at .040 inch thick. These work but do demand high quality surfaces and careful operating attention of avoid engine overheating, so while functional they are edgy to use especially where many if not most guys don’t put much effort or financial resources into the cooling system unless the engine cooks itself during some outing. Generally since composite or MLS gaskets offer a greater service range without failure risk the answer to the excessive gasket thickness some of which hit over .050 inch is to allow their use be decking the block or using raised crown pistons or some combination thereof to get the sum of the piston crown to chamber step clearances back into the .035 to .045 inch range.

In view of best burn while trading squish/quench clearances and compression ratio, it is well recognized that a flat top piston offers the best burn characteristics thus best power and lowest fuel consumption doing it. Since keeping the squish/quench clearance is critical to detonation resistance where the best available street fuel top out at 91 octane in most communities and 93 in a few places, this often drives the use of piston reliefs to adjust the compression ratio to the available octane. In this regard a D dish or a stepped crown piston where compression relief volume is placed under the valve pocket is far superior than the use of a circular dish that increases the squish/quench clearance under much of the chamber step. Another thought to be considered with striker builds is the use of 74-76cc chambered aftermarket head’s and a flat top piston. Aftermarket head’s with these larger chambers unlike factory production head’s retain the shapes of the Ricardo heart shape chamber for best burning characteristics. This to be differentiated from what the factories did by just making wide open 74-76cc chambers to drop compression ratios and intentionally slow the burn to reduce operating temperatures as a means of reducing NOx pollution at the significant cost of power and efficiency.

So in total these are some of the considerations you need to look at before committing money to parts.

Bogie
 
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