We're used to the unexpected from World Products--things like 454-cube small-blocks and big-blocks with cylinders large enough to warrant their own ZIP codes. But this is something altogether new and unprecedented--a traditional small-block-based engine topped off with LS cylinder heads.
Can't be done, you say? If you were to try such a combination with a standard GM small-block or even one of World's regular Motown small-block castings, you'd be right.
But World has gone and mixed with the natural order of the universe and redesigned the small-block to not only accept the LS head's bolt pattern, but match its water passage design. The result is a small-block on the outside that incorporates LS compatibility where it counts.
They call it the Motown LS. If your head is still swimming about this, consider the reasons for engineering such a hybrid:
* It allows the small-block to produce new, extreme levels of Streetable power that were almost unattainable with traditional small-block heads
* It offers a tremendous performance advantage to racing classes that demand a distributor-triggered ignition system
* Installation in older cars and race cars is a snap because the small-block oil pan and motormounts are unchanged
"As much as the small-block and LS are different, there are some key similarities that make it work," he says. "It's clear when you examine the LS engine that there is a direct path back to the SB2 engine--an extension of the small-block design."
Among the key enablers of this small-block/LS hybrid is one of the very details that GM instilled with the LS architecture: the small-block's 4.40-inch bore centers. That means the heads' combustion chambers are located perfectly above the bores.
Also, an LS-style camshaft fits inside the small-block cam holes. All that's needed is a distributor drive gear on the back of it and fuel pump lobe on the front. (World got Comp Cams to build one for the engine seen in this story.)
Surprisingly, what's remarkable about the Motown LS isn't what's new about the engine, but what is carried over from one engine or the other. That includes:
* Standard small-block crankshaft
* Standard small-block connecting rods
* Standard small-block distributor and timing gear
* Standard LS pistons (pinned to the SB rods without modification)
* LS hydraulic roller lifters
* LS valve springs and z rocker arms
And because World casts the Motown LS block with the standard LS deck height of 9.240 inches, off-the-shelf LS intake manifolds bolt on without a hitch. There are some unique pieces that make this combination work, of course. They include:
* A camshaft with LS lobes, but small-block-specific fuel pump lobe and rear distributor drive gear
* 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
Inside The Block
The key to making the hybrid engine work is World's Motown LS block, which is designed for the water flow characteristics and bolt pattern of the LS head. Check the accompanying comparison photos and you'll see the obvious differences: the deck of the Motown LS looks like an LS deck because of the water passages.
The block also incorporates important oiling circuit changes that World also bakes into its new Motown II casting--its "standard" small-block. Those changes include a redesigned, priority-main feed system; relocated cam journal oiling holes from the 6 o'clock position to a 5 o'clock position; and oil restrictors moved to the middle of the lifter valley.
World called Comp Cams to build a hybrid stick to match its hybrid engine. The details are, at first, a little confusing, so pay close attention: The Motown II/Motown LS block is designed to accept the larger, 55mm cam size of the LS, which seemed a natural for this engine. However, because of the large, 4.000-inch stroke, a smaller-diameter cam was needed, so Comp built a standard small-block-sized cam with LS lobe and small-block fuel pump lobe and distributor gear. Got it?
As for the cam's specs, it delivers about 0.650-inch lift on the intake side and 0.660-inch on the exhaust side, with duration of 250/255 degrees. With those high-flow heads and big, 427-inch engine displacement, a big cam was certainly needed.
With the camshaft 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 lower in the small-block than an LS engine, and the deck is significantly higher than a regular small-block, neither regular-length LS pushrods nor small-block pushrods are usable. The Motown LS uses 8.200-inch-long pushrods. Stock small-block length is about 7.800 inches, while stock LS pushrods are about 7.400 inches long.
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 small-block parts. The 6.125-inch-long rods don't even require machining in order to be pinned to the LS pistons.
Cylinder Heads & More
The heads used with the Motown LS block are World's Warhawk LS1 units (ported for the engine used in this story by noted Ford race engine builder Jim Kuntz). They bolt to the block in production LS fashion, meaning four bolts per cylinder. Although the Motown LS block has sturdy iron decks, the four-bolt pattern isn't the best for high-boost combinations. We'll just have to wait for World to make a block that supports its six-bolt LS7-X heads.
The cathedral-port, 15-degree Warhawk LS1 heads have 235cc intake runners and flow very well out of the box, but they really responded to the port work conducted by 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 unique comes into focus, something that has never before been built.
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 the small-block distributor simply drops through the valley cover.
Spark plug wires are not conventional, however. Because of the differences in spark plug locations between LS and small-block heads, standard small-block wires don't quite fit. And, of course, the distributorless LS ignition system uses only the shortest of leads between the coil pack and plug, so cut-to-fit universal wires are required.
The Motown LS uses the LS-style firing order of 1-8-7-2-6-5-4-3.
We didn't only document the first Motown LS engine during its assembly, we followed it into one of World Products' dyno cells and witnessed its very first test session.
After a brief warm-up/break-in period, the engine produced an eye-opening 629 hp/579-lb-ft result. That's about 70 hp more than one of World's regular Motown small-block 427 engines and about 15 horses more than their typical Warhawk LS combos.
Everyone on hand for the test was understandably impressed with the results, but surprised even by its performance over their Warhawk LS combinations with similar specs.
"I have to give credit to Jim Kuntz for working on the heads," said Bill Mitchell. "They flow great, but he has a lot of experience with the design, because it's so close to the Ford design."
As for the performance above and beyond a conventional small-block setup, it was pretty much what Mitchell expected.
"We've seen the difference between 427-inch Motown and 427-inch Warhawk engines, so the results are in line with what we predicted," he said. "It just proves that the LS design is head and shoulders above the small-block head design when it comes to airflow."
The implications for the Motown LS are far-reaching, particularly for racers who are required to run a distributor. As for street enthusiasts, it is performance that was virtually unattainable in a naturally aspirated small-block combination. In fact, the only small-block crate engine in World's arsenal that makes more power than this pump-gas, streetable engine is their 13.5:1, race-gas-sipping Drag Race 427 that is rated at 650 hp.
Considering the Motown LS made about 630 on its first pull, it's not out of the question that with tuning it would equal the Drag Race 427 with 10.7:1 compression and premium pump gas.
By the way, the Motown LS isn't merely a concept. World Products is ready to go with crate engines, engine kits and the like.
It's the ultimate hybrid.