Shown in the image on the left is a four-bolt main from a stock 400 block, and on the right is our Dart unit. The main difference is that the stock unit utilizes a straight-down, parallel fastening configuration for the main caps, which puts a ton of load on the block's main section. The Dart unit utilizes a splayed fastener on the outer portion, putting stress into the more beefy area of the casting, creating a stronger clasp and deterring the main cap from walking (moving under load).
To anchor the foundation, we called upon Dart Machinery in Troy, Michigan. The professionals at Dart suggested the Little M block, which is a high-performance block that can be used with standard off-the-shelf (stock-type) SBC components. The Little M is cast from high-strength iron and beefed up in critical locations where a stock block would normally fail. We opted for the 4.125-inch bore with SBC 400 mains. Now all we need are the components to aid in assembly of the bottom end.
For the rotating assembly, we called upon the folks at Lunati in Olive Branch, Mississippi. Lunati has been known for years for providing racers with quality crankshafts, connecting rods, camshafts, pistons, and valvetrain components. Lunati is under new ownership, vowing to return to its roots, supporting racers like never before. After conferring with the technical specialists at Lunati, we decided to build a 400ci small-block. For this we will employ Lunati's fully machined 5.7-inch connecting rods, Pro Series-4340 forged steel crankshaft with 3.75-inch stroke, and a custom set of forged Pro Tru Wiseco pistons with a -20cc reversed dome (dish) for lower compression. Blower engines require a lower engine compression to operate safely. Forced air into the cylinder can create disastrous results due to higher cylinder pressures if the combination is not correct.
As with any build, camshaft selection is critical-more so when you are looking to make over a thousand streetable horsepower. After discussing camshaft options with the staff at ProCharger, it was suggested that we give Steve Morris Racing Engines (SMRE) in Muskegon, Michigan, a buzz. Steve builds some crazy ProCharged combinations that lay down serious horsepower. It is not uncommon for SMRE to build a 1,000-plus-horsepower ProCharged SBC to run on pump gas with hydraulic lifters.
With this kind of knowledge and experience building ProCharged blower combinations, we decided to score a custom solid roller bumpstick from SMRE with a conservative lift of 0.668-inch on the intake and 0.672-inch on the exhaust. Duration checked in at 264 on the intake and 272 on the exhaust. Normally one would think the more lift the better when making power levels as such, but with the progression of camshaft technology, that is not the case.
DiSomma now checks the diameter of the crankshaft mains via a micrometer. This is critical when determining the main bearing clearance, as well as checking the uniformity of the crankshaft grind. Once the crankshaft is measured, a bore gauge is employed to measure the main bore, but not before the main bearings are installed and the caps are torqued. Once the measurements are calculated, the bearing clearance can be obtained. We are looking for a main bearing clearance of 0.0030-0.0032-inch. While this is slightly larger than the standard passenger car, it will be fine for our blown mill, which will utilize a thicker oil than normal. Thus far all measurements have checked within range.