GM's LS engine is a powerhouse, thanks to great-flowing heads that enable tremendous horsepower and high-rpm performance. But while the LS is becoming a more popular swap choice for earlier, pre-C5 cars, it's not a direct bolt-in.
Wouldn't it be great, then, to marry the power-building capability of the LS engine with the bolt-in ease of the classic small-block Chevy? World Products' Bill Mitchell thought the very same thing.
"Our 427-inch Warhawk LS crate engine makes about 50 more horsepower than our comparable Motown 427 small-block with essentially the same induction system," Mitchell says. "The basic design of the LS head is really that much better than the small-block design, and we wanted it for the small-block."
The first piece of the Motown...
The first piece of the Motown LS puzzle is World Products' redesigned Motown II LS cylinder block, which adapts LS heads via the water passages and bolt pattern. It also mounts a mechanical fuel pump, has sturdy four-bolt mains, and uses an early-style two-piece rear main seal.
For just about any other engine builder, such details would be insurmountable obstacles, but World Products isn't just another engine builder. The company manufactures its own cylinder blocks, heads, and more, so it's in the enviable position of being able to direct the design of its products. And that's just what it did, redesigning the SBC casting to accommodate LS heads.
The result is the Motown LS.
It's difficult to overemphasize the engineering feat this mill represents. If you're familiar with the basic specs of the SBC and LS engines, you know the small-block's water jackets don't remotely match the water passages in LS heads, and let's not forget the incompatible head-bolt arrangement. Also, the deck height of the small-block is much lower than that of the LS, making intake-manifold installation problematic.
World Products addressed all those issues, and the finished product performs beautifully. We know-we saw the first one assembled go on the dyno and make nearly 630 normally aspirated horsepower.
Of course, World approached the project methodically. Bolstering viability was the fact that GM designed the LS with the same 4.40-inch bore centers as the original small-block. As a result, the LS combustion chambers would align perfectly over the SBC cylinders.
"As much as the small-block and LS are different, there are some key similarities that make it work," Mitchell says. "It's clear when you examine the LS engine that there's a direct path back to GM's SB2 racing engine, an extension of the small-block design."
Also helpful was the fact that an LS-style camshaft fits inside the small-block cam holes; in fact, the journals align almost perfectly. All that's needed is a distributor-drive gear on the back of the cam and a fuel-pump lobe on the front. (World got Comp Cams to build one for the engine seen in this story.)
These comparison shots illustrate...
These comparison shots illustrate the significant water-jacket differences between the Motown II LS block (bottom) and the conventional Motown II (top). An LS-style water pump is required.
To adapt the LS heads, World redesigned the small-block's water jackets to match the newer design. The company also raised the deck height to an LS-spec 9.240 inches-enabling standard LS intakes to bolt on without a hitch-and redesigned the block's valley to accommodate LS lifters.
Perhaps most remarkable of all is the number of off-the-shelf parts that can be sourced from either a small-block or an LS, including:
* Standard SBC crankshaft
* Standard SBC connecting rods
* Standard SBC distributor and timing gear
* Standard LS pistons (pinned to the SB rods without modification)
* LS hydraulic roller lifters
* LS valve springs and rocker arms
Of course, there are some unique pieces that make this combination work. They include:
* A camshaft that combines LS lobes with an SBC-specific fuel-pump lobe and rear distributor-drive gear
* A top-of-engine valley-cover plate that mounts the top of the heads and the distributor
* Custom-length, 8.200-inch pushrods
* Adapter plates that bolt to the front of the heads for production-style accessories and water-pump mounting
Block and cam details
Examine the accompanying comparison photos closely and you'll see the obvious differences between the Motown LS and a conventional small-block. Most notable are the decks, which look like LS decks.
A look at the block's valley...
A look at the block's valley reveals the redesigned lifter bores, which were configured to match the configuration of production LS components. The block also incorporates the oiling-system changes of World's conventional Motown II block, meaning the oil restrictors are moved from the rear of the block to the valley for easier access. The cam-journal oil holes also are relocated to ensure adequate flow with high spring pressures.
A standard SBC crankshaft...
A standard SBC crankshaft is used without modification. In the case of this first Motown LS build-up, it's a 4.00-inch stroker that will complement 4.125-inch bores to deliver a 427-cube displacement. The reduced windage of the SBC design over the LS deep-skirt block frees up horse-power, enhancing the Motown LS' output.
More inexpensive SBC parts...
More inexpensive SBC parts on the bottom end include the oil pump and pick-up. Because an off-the-shelf crank and oil pan are used, nothing exotic is required for their complementing parts. It also means installation in a car already equipped for a small-block is a no-brainer.