The Motown LS requires a custom...
The Motown LS requires a custom camshaft-a hybrid of an LS hydraulic roller design that works in the SBC cylinder block and actuates the LS valvetrain. And to satisfy the big heads, it's a hairy one, spec'ing out at 0.650/0.660-inch lift and 250/255-degree duration.
The block also incorporates important oiling-circuit changes that World also bakes into its new Motown II (conventional SBC) casting. Those changes include a redesigned, priority-main feed system; relocated cam-journal oiling holes (from the 6 o'clock to the 5 o'clock position); and oil restrictors moved to the middle of the lifter valley.
Advantages of the changes include:
* Camshaft oiling is not affected by high valve-spring pressure
* The distributor is fed at the end of the oiling cycle, reducing the chance of oil-pressure loss through distributor O-ring leakage
* The relocated oil restrictors can be changed without removing the transmission, converter, or clutch
The Motown II/Motown LS block is designed to accept the larger, 55mm cam size of the LS. However, because of the large, 4.000-inch stroke used on our 427ci test engine, a smaller-diameter cam was needed. World called on Comp Cams to build a standard SBC-sized cam with LS lobes, along with a small-block fuel-pump lobe and distributor gear.
A standard LS cam (top) is...
A standard LS cam (top) is shown here with the custom bumpstick from Comp Cams. Note the redesigned rear end, where the distributor drive gear is grafted. At the front is a fuel-pump lobe.
With the cam and heads in place, the rest of the engine combination falls together quite easily. The Motown LS block is designed to use LS lifters, which slip into the block small-block-style rather than the pocketed style of production LS engines.
Because the camshaft is mounted lower in the small-block than in an LS engine-and the deck is significantly higher than a regular small-block-neither regular-length LS nor SBC pushrods are usable. Instead, the Motown LS uses 8.200-inch-long pushrods.
Inside the block, LS-style dished pistons are matched with the Warhawk cylinder heads. They use production-type metric piston rings, which appear to work very well in the small-block, with minimal friction. The connecting rods and crankshaft are off-the-shelf SBC parts. The 6.125-inch-long rods don't even require machining in order to be pinned to the LS pistons.
High-flow heads
The heads used with the Motown LS block are World's Warhawk LS1 units, with production-style four bolts per cylinder. Their cathedral-port, 15-degree design has 235cc intake runners and flows very well out of the box, but they really responded to the port work conducted by Jim Kuntz.
Off-the-shelf forged LS pistons...
Off-the-shelf forged LS pistons for the 4.125-inch bores are used with LS-type metric rings. Compression is a pump-gas-compatible 10.7:1. The connecting rods are standard SBC fare.
Just as important to the engine is the unique valley cover that mounts the top of the heads. It's when the heads are bolted onto the small-block and valley cover that the picture of something truly unique comes into focus.
The remainder of the assembly process is pretty much like buttoning up a standard LS or small-block. A regular LS intake manifold bolts right up, and a standard SBC distributor simply drops through the valley cover. You could even install electronic fuel injection if you wanted.
The spark-plug wires are not conventional, however. Because of the differences in plug locations between LS and SBC heads, standard small-block wires don't quite fit. And, of course, the distributorless LS ignition system uses very short leads between the coil packs and plugs. As a result, cut-to-fit universal wires are required.
By the way, the Motown LS uses the LS-style firing order of 1-8-7-2-6-5-4-3.
Here, the LS lifters are lowered...
Here, the LS lifters are lowered into the block SBC-style, rather than the pocketed design of an LS engine. The block was designed for the LS lifters; this wouldn't work on a standard small-block.
On the dyno
Along with documenting the assembly of the Motown LS, we took in the inaugural dyno test. After a brief warm-up/break-in period, the engine produced an eye-opening 629 hp and 570 lb-ft of torque. That's about 70 hp more than one of World's regular Motown small-block 427 engines and about 15 horses more than a typical Warhawk LS combo.
The significant jump in power over a conventional small-block didn't surprise anyone, but the degree to which it over-performed did.
"We were really pleased with it," Mitchell says. "It validates our idea and proves the airflow of LS heads is superior."
 This unique valley-cover plate...  This unique valley-cover plate is one of the key components of the Motown LS assembly. It secures the upper portion of the heads and provides a mounting location for the distributor. The valley cover has a removable top section that allows easy access to the lifters. |  Here's World's Warhawk LS1...  Here's World's Warhawk LS1 heads being installed on the small-block. Port work was handled by Jim Kuntz, who's a whiz with Ford Windsor-style heads, which mirror the LS design in many ways. The heads are bolted to the decks and the unique valley cover. |  Production LS valvetrain components,...  Production LS valvetrain components, including the rocker arms, are used, but the combination requires custom, 8.200-inch pushrods because of the non-LS cam position. |