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."
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.)
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.
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.
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.
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.
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.
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."
But what about the power increase over World's own LS engine? It wasn't all due to a simple port job on the heads. Mitchell reminded us of the differences between the SBC and LS cylinder-block designs. The LS block has a deep-skirt design (also known as a "Y" block"), while the small-block casting extends only to the crankshaft centerline.
The LS block design enhances overall rigidity, which is particularly helpful with OEM aluminum castings, but it creates considerably more crankcase windage than the small-block. The Motown II block is plenty stiff to begin with, with thicker-than-stock key features (bulheads, "China" walls, and more) and four-bolt mains.
"Windage makes a huge difference," Mitchell says. "With this combination, you've really got this best of both worlds-an affordable, performance-oriented bottom end and the great breathing of LS heads."
The implications for the Motown LS are far-reaching for street and racing enthusiasts-and exciting. Just imagine this monster in a C3 or C4 Vette.
World Products deserves an achievement award for the Motown LS, and enthusiasts everywhere are the beneficiaries of the company's progressive attitude toward building big power.