The success of the small-block Chevy, as a street engine and a reliable, all-out racing powerplant, has been documented in the pages of magazines, such as SUPER CHEVY, and on the trophies of drag-race and circle-track competitors since the mid-1950s.
In the decades since the small-block was introduced, backyard mechanics and professional race engine builders alike have exploited the engine's tremendous potential, but even the venerable small-block has its limits. As with many engines, overboring the small-block can present water passage concerns if the builder really wants to hog-out the cylinders. And while the strength of a four-bolt-main block is universally desired, cores are getting harder to find.
Despite these challenges, engine builders have worked around the small-block's limitations and made great power. But now there is a new small-block on the... uh, well, block--one that improves on the admittedly few shortcomings of the standard Chevy block.
Welcome to MoTown
World Products' all-new four-bolt-main MoTown block is a brand-new casting based on the venerable Chevy small-block. World Products cut their casting teeth in the early '90s with the Merlin block. Based on the Chevy big-block, the Merlin block has become a staple of serious racers, both on pavement and on water.
"We learned a lot on the Merlin block and transferred it to the MoTown," says World Products President, Bill Mitchell. "The features that made the Merlin stronger than the regular big-block, we applied to the design of the MoTown."
Although not a structural feature, the casting process for the MoTown (and its sister, the Merlin II big-block) is just as important as the finished product. Why? Because it significantly impacts the enthusiast where it counts--the wallet.
"When we started with the Merlin, we could only pour one block at a time," Mitchell says. "But now, we've got the tooling to pour two blocks at once. This greatly reduces the end cost to the consumer."
The tooling for the MoTown block is a cast-iron behemoth that, according to Mitchell, "is bigger than my office." To maintain OE-type tolerances and specifications, the MoTown blocks are cast in high-density 2800 Gray Iron, including .05-percent of nickel--just like the tin blocks the General used to make. The nickel content makes for harder and stronger cylinder walls. Also, the manufacturing process utilizes only two fixturing operations, which means tighter, more consistent tolerances for every block cast. The whole process conforms to OE-supplier, QS-9000-quality specifications.
The MoTown blocks, while cast with some significant changes compared with the standard Chevy block, are designed to accept any aftermarket small-block part, as well as all Chevy accessories.
"We put in every bolt hole that General Motors ever did to the small-block," says Mitchell. "Some of them, I don't even know what they're for. I think one was designed only for a spark plug loom on a truck application, but we put it in."
Despite its faithfulness to the original small-block's mounting locations, a close-up examination reveals the MoTown's unique features. The most obvious is the bulged cylinders, which were designed with more "meat" around them to accommodate generous overbores.
The MoTown is available with either a 4.00-inch or 4.125-inch bore. Well, that's not quite true. The blocks are delivered with bores .010-inch undersized, requiring some final honing by the builder to reach the desired bore. Mitchell says the bores will safely expand to 4.200-inches, but there aren't many options when it comes to head gaskets for such cavernous cylinders. "A 4.175-inch bore will work with existing Fel-Pro gaskets," he says.
Even with a 4.200-inch bore, there's still a .250-inch wall thickness between the cylinders. The extra iron around the cylinders provides ample water-jacket room, and the head bolts go in "blind"--meaning they don't go into water, thereby reducing the risk of leaks.
There's added thickness to the front and rear bulkheads, too. "Think about it," Mitchell says. "These are the weakest parts of the block, what with the holes for the cam and crankshaft. I've seen some Pro-Mod guys disassemble motors that, once the oil pan and intake were removed, fell into two pieces."
To shore up the new small-block's rigidity, an inch of iron was added to each bulkhead. The extra metal adds inner dimension to the block, but not so much that it interferes with the crank's counterweights. In fact, even with the added bulk of the meatier cylinders and thickened bulkheads, the MoTown block has just about the same exterior dimensions as the standard Chevy block, so clearance in tight engine compartments isn't a problem.
The added bulk of the block doesn't mean it's overweight, though. The MoTown tips the scales at 190 pounds with the main caps installed.
Speaking of the main caps, the MoTown small-block employs four-bolt nodular iron caps, located with dowels as its preferred method of holding up the crank. World Products will deliver the block with splayed, billet caps, if desired, but Mitchell says the nodular caps are the hot setup.
"Nodular caps require more expensive tooling to manufacture, but are less expensive to the consumer," Mitchell says, "But they're stronger than billet caps. There's elasticity with them, too, which billet doesn't have when the block heats up. That extends the crankshaft's life."
Locating the nodular caps with dowels in the block, rather than a splayed bolt pattern promotes truer roundness of the mains.
"We examined the engines that Caterpillar builds, and they've got nodular caps located with dowels," Mitchell says. "Those are huge motors with lots of stress that are designed to run almost forever. Those are the design characteristics we were looking for."
The MoTown block is full of other high-performance, high-endurance features, including indexed lifter bores, which ensures accurate cam degreeing on both sides of the engine; priority oiling, whereby the crankshaft receives oil first, then the camshaft; wide, solid pan rails that can be clearanced for stroker cranks up to 4.250-inch without hitting water; integral bosses, front and rear, for front-feed and dry sump oiling systems.
World Products will deliver the blocks either completely bare or prepped with cam bearings, freeze plugs, block-plate honing and a thorough wash. Of course, complementing the MoTown block is a range of MoTown cylinder heads, and World Products has even introduced a 415ci crate motor based on these products.
In future issues, we'll delve inside the MoTown heads and even follow the build-up of a 415 crate motor. In the meantime, check out the accompanying photos and captions, which provide more of the MoTown block's interesting details.
It seems hard to believe, but after 46 years, the small-block is all new.