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Where's the Boss?Why doesn't the ZZ502 crate motor from GM have the fuel-pump boss machined into the block? The 454 H.O. has the boss, and from what I can gather it's also a Gen VI block like the 502. What's the deal?Gary CooperRancho Cucamonga, CA
We spoke with Kevin McClelland of Flowmaster, who was involved in the development testing of the Gen V and Gen VI Chevrolet big-block engines. He explained that the 454 and the 502 are each unique castings, not differently machined versions of the same casting. When the Gen V was introduced (for 1991), neither the 454 nor the 502 had fuel-pump bosses. These engines were intended for then-current applications, which all used electric fuel pumps. At the time, the older Mark IV engines were still being serviced with new Mark IV blocks. However when the Gen VI was developed, the fuel-pump boss returned to the 454, as you've observed. This was done because the Gen VI 454 also had to serve as a service-replacement block for all previous 454-equipped vehicles, many of which had carburetors with mechanical fuel pumps. Since the 502 was never intended for production use, the boss was left off.
Misguided RockerI've been reading a lot in your magazine and others about GM Vortec cylinder heads and the performance advantage they offer over other GM heads. I may be able to get my hands on a set that came off a low-mileage engine that was replaced under warranty. However, I'm confused about one issue. I understand that a specific intake manifold is needed, but what's the deal with the rocker arms? Most articles written on the subject say that later "guided" rocker arms are needed, but why? All of the small-block Chevy engines I've worked on operate without guided rockers or any sort of pushrod guideplates, so why the sudden need? Couldn't I just transfer the original rockers from the '76 350 in my '68 Chevelle to the Vortec heads? I don't plan on running a big cam or turning high rpm, so what's the problem?George WestfieldBoulder, CO
Actually, the small-block Chevys you worked on did have pushrod guides, just not the type you're accustomed to seeing. True, there aren't bolt-on guideplates on stock small-blocks, but the holes in the heads that the pushrods pass through act as guides. Take a closer look at an older set of heads and you'll see that the holes are not round, but slightly oval with flat sides. In later years, engineers decided to make the pushrod holes round and larger so as not to interfere with the pushrods at all. To replace the guiding function, the rocker arms were redesigned with a grooved tip. The grooved, or guided, rockers look nearly identical to earlier unguided examples except for the tip. You will definitely need them if you upgrade to Vortecs, but a set of 16 brand-new arms, complete with new fulcrum balls and locknuts costs only around $40 from GM. If you're really scrounging, check late-'80s/early-'90s small-blocks in the local boneyard or machinist shop core pile, as some of these also used the guided arms.
Spare Parts, Part OneI am currently in the process of rebuilding a '77 350 for my '64 Impala SS. When I was comparing '68 327 rods and pistons to those of the 350, I found them to be exactly the same. Is it possible to use these 327 rods and pistons in a 350? Would there be any problems?Matt CroxtonValley Head, AL