EngineLabs: What design and structural features on the World Products Motown II Raised Cam cylinder block make this block stronger than stock or other race blocks?
Jack McInnis: The camshaft location is raised in the block by .134-inch, which offers several advantages without the need for a lot of special parts. This block features a standard 9.025-inch deck height and is cast in the USA from World’s high-density iron alloy. It comes with either 3.995-inch cylinder bores to finish at 4.000-inch, or 4.120-inch bores which finish at 4.125. You also have a choice of 350 or 400 mains with either nodular or billet steel 4-bolt caps. The main caps have splayed outer bolts which strengthen the bottom end by tapping into the pan rail area of the block which has more material than the main webs themselves.
One of the recent updates we’ve made to this block is to change the main cap studs from 1/2-inch to 7/16-inch diameter. This feature strengthens the main webs because the holes are smaller in diameter and also their depth is reduced by .150-inch, leaving more material (and strength) in the main web. We felt this was a beneficial change because it is very rare to see a main stud failure in a small block, and the added material in the webs just makes the whole bottom end that much stronger. We also use high quality ARP fasteners to improve the bottom end strength.
Some of the other features which increase the Motown’s strength are the .600-inch thick decks with blind tapped head bolt holes, and the siamesed cylinder walls which are nominally .250-inch thick at the 4.125 bore diameter. This feature not only adds critical strength, but can actually increase horsepower due to the improved ring seal which results from a more rigid cylinder wall.
EngineLabs: What are the benefits of raising the camshaft location?
McInnis: The primary benefit of raising the cam location in the block is that it provides increased clearance between the rotating assembly and the camshaft. This allows you to use much more robust components which provide higher strength and stability. For example, using a 4.000-inch stroke crankshaft to increase displacement in a small block to 427 or 434 cubic inches has the potential to produce a substantial gain in power. In order to feed the larger displacement enough air/fuel mixture a more aggressive cam profile will be required, and to hold things together a stronger rotating assembly will be needed. The problem is that when you increase the stroke, the rod journals of the crankshaft will swing much closer to the camshaft at the top of the stroke. Consequently, you have to find ways to prevent the big end of the connecting rods from making contact with the camshaft – this means using rods with a smaller big end profile and using a small base circle cam. The smaller rods are going to reduce the ultimate strength, meaning your expensive big-inch engine is at greater risk of blowing itself to bits. The small base circle cam is also less rigid and coupled with the higher valve spring loads associated with an aggressive cam profile, the cam is subject to flexing and twisting. This means the valve train is not actually achieving the correct lift and valve timing events it was designed for.
Raising the cam location alleviates these issues. Now instead of requiring a smaller than stock cam, we can use a larger than stock BBC cam core, or a 50mm. This not only increases the rigidity of the camshaft, but also allows much more effective lobe profiles with improved ramp area to provide better control over the valve train. At the same time, we can use larger H-Beam connecting rods for increased bottom end strength. It’s a win-win situation.
EngineLabs: A raised cam also means some special parts are required. Can you explain?
McInnis: With the Motown II RC, you will need a different timing set to accommodate the .134 increased distance between the crank and cam centerlines. Other than that, all the normal small block stuff will fit. A standard SBC style oil pan, oil pump & filter, timing cover all fit. This keeps costs down compared to the “Rocket Block” style raised cam blocks which raise the cam by .391-inch, and require special timing sets, special oil pans, remote oil filters, etc.
EngineLabs: What other features about this block will engine builders appreciate?
McInnis: The fact that the block is machined with a BBC cam journal opens up a wider variety of choices in available camshafts and helps the engine builders to offer their customers an even more affordable package. Raising the cam location prompted us to fit the block with lifter bushings as well, in order to ensure proper oiling system performance. We use high quality American made flanged bushings in standard .842-inch diameter, or you can order the .904-inch upgrade at no extra cost.
Some of the other features that will appeal to the engine builders include World’s priority main oiling system which lubricates the main bearings first for high-rpm reliability. The water jackets are enlarged for better cooling capacity and a standard style oil filter pad and fuel pump boss are provided.
EngineLabs: What are the targeted markets for this block?
McInnis: This block will appeal to small-block drag racers and circle-track racers, as well as serious street performance enthusiasts. It offers some significant improvements without breaking the bank.