Have a 502 BBC that I am confused on. Block Casting #10237300 Side of block cast 8.2 6 Bolt timing cover GM Performance Aluminum Heads This should be a gen VI block according to the above, but has no fuel pump boss like a Gen V. Problem is the engine runs real hot, and the last shop it was at, re-did the heads and installed what I think are the wrong head gaskets Fel Pro #502SD, which is for Mark 4. From what I gather, the GM Performance Bow Tie heads will work on all big blocks, but have to use different head gaskets if used on a Gen V or VI. Where I am confused is all that I See is Gen VI blocks had the fuel pump boss reinstalled. So what is this block?? Help! Bill
Google is your FRIEND ! Gen 5: General Motors made substantial revisions to the Mark IV engine, and the result was christened "Gen 5" when it was released for the 1991 model year as a 454. There were 502 cu. in. versions, but never installed in a production vehicle, the 502s were over-the-parts-counter only. Changes to the Gen 5 as compared to the Mk IV included, but are not limited to: rear main seal (and therefore the crankshaft and block) were changed to accept a one-piece seal, oiling passages were moved, the mechanical fuel pump provisions were removed from the block casting, the machined boss for a clutch bracket was eliminated, the cylinder heads lost the ability to adjust the valve lash, and the coolant passages at the top of the cylinder block were revised. The changes to the coolant passage openings meant that installing Mk IV cylinder heads on a Gen 5 block could result in coolant seepage into the lifter valley. Frankly, the changes (except for the one-piece rear main seal) were all easily recognized as cost-cutting measures which also removed some quality and/or utility. All told, the Gen 5 engine was not well regarded by the Chevy enthusiasts because of the changes to the coolant passages and the lack of an adjustable valvetrain. As always, the aftermarket has provided reasonable fixes for the problems. The Gen 5 lasted only until 1995. Gen 6: GM recognized that it did not make any friends when it designed the Gen 5, and so they chose to revise the coolant passages again when designing the Gen 6, allowing the older heads to be used without coolant seepage problems. The boss for the clutch bracket returned, but was generally not drilled and tapped. The non-adjustable valvetrain remained, as did the one-piece rear main seal. Some but not all Gen 6 454 (and not 502) blocks regained a mechanical fuel pump provision. Production engines installed in pickup trucks got a high-efficiency cylinder head, still canted-valve, but with a modern heart-shaped combustion chamber of about 100cc. The intake port has a "ski jump" cast into it to promote swirling of the intake air flow. All production vehicles with a Gen 6 used a 454 version, but over-the-counter 502s are available. The Gen 6 is sometimes referred to as the "Gen Fix" because it fixed a number of issues that disappointed enthusiasts when the Gen 5 was released. As an added bonus, most if not all Gen 6 engines use hydraulic roller lifters.
OH CRAP ! I am NOT squirrel...…. Just a Mangy Flea Bitten Junk Yard Dog ! so NFM the last post...……… LOL
that's all right, I don't know the story with the later engines, I have only messed with the Mark IV big blocks. I'd have to google it, and find the answer that you've already found. (on the road, in Las Vegas right now, visiting friends)
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