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THE MOTOWN II A world of difference

If you are a fan of the venerable Chevy small block, or as it is known the “mouse motor”, then you know there are plenty of aftermarket versions of the original GM-designed cast iron version. If you have the need and the bucks you can get cast aluminum versions or carved out of a solid chunk of billet aluminum that will allow the user to build an engine any size he wants or needs up to 500 cubic inches.

General Motors, Dart and World Products are the acknowledged standards when it comes to the manufacturing and design of aftermarket cast iron Chevy small blocks. In this tech feature we are going to take a look at the newest offering from Bill Mitchell’s World Products foundry.

For almost 25 years Mitchell’s World Products have offered enthusiasts a variety of cast iron versions of both the basic 350 and 400 Chevy blocks. In 2008 the tooling used to produced those blocks reached the end of their wear cycle and had to be replaced.

These “tools” ain’t cheap, brother. Ordering and making new ones cost Mitchell’s company north of a half-million bucks, so Bill figured if he was going to have to spend that kind of cash he should not just duplicate the blocks he had been producing up to last year but, instead, make new tooling that would deliver a block with all of the problems they had found with the block over the last 25 years solved or improved.

So they re-designed their Motown small block, called it the Motown II, and recently started delivering them.

The new block has improved designs that include a priority-main bearing oiling system that provided better lubrication to the main bearings, cam bearings, and valve lifters.

In case you may not understand the science behind a priority oiling system here is a quick explanation: The small-block Chevy ignition distributor is located in the passenger side oil gallery. That galley supplies the oil to lubricate the valve lifters. Because the distributor shaft requires rotational clearance, that clearance creates a drop in oil pressure when it fills with oil. The oiling system of a small-block Chevy is located at the back of the block.

Oil is delivered from the pump in the oil pan up to the oil filter and from there through the main feed passageway that on an OEM block crosses over in the back of the block and feeds the lifter gallery. If the distributor shaft O-ring is damaged or the distributor itself is out of alignment because the intake manifold (which holds the distributor) is crooked allowing more oil to bypass the O-ring, engine oil pressure could be further reduced, especially when the oil gets hot and thins out. 

To try and solve this issue relating to stock block design, the oiling system routing of a World Motown II block has been changed. Instead of feeding the lubricant into the lifter oil galleries first, it is directed to a new passageway cast high into the middle of the World block. From there it crosses over to both sides of the block forming an H pattern and, finally, to the distributor. Though World has the same distributor “leak” as everyone else, all the important components, the main bearing, rod bearings, cam bearing, and lifters, have received their oil under the right pressure.

Also, should you wish to alter the size of the blocks’ oil restrictors to equalize oil distribution, on the Motown II block you can access them by simply removing the intake manifold. On some Chevy blocks you have to remove the transmission, the bell housing and the flywheel before you can access the oil restrictors at the back of the block.

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