The EngineEven with the great e.t.'s I'd found, I wanted more performance. It was time to look deeper into the bottom end. I was instantly inspired by the 4.00-inch stroker crank from Mopar Performance. When I saw that Diamond Racing had stepped up with pistons made specifically for this crank, I knew this combo had a home under the hood of my truck. With that decided, I developed a plan for an engine that had "street warrior" written all over it. Ingredients would include a 360 Magnum block, the 4-inch stroker crank, a set of Eagle SIR rods, and Diamond Racing's slugs. I called Ron Beaubien at Diamond and told him what I wanted to do and how I wanted to accomplish it. Ron informed me that Diamond's machine shop could ship me a balanced rotating assembly that included the crankshaft, pistons, wrist pins, connecting rods, piston rings, and main/rod bearings.
Sold!Next, I located a good donor block, which I took to my friend Randy Williams at Triangle Auto and Machine. Randy magna-fluxed the block, resurfaced and squared the deck, bored the cylinders .030-over, and honed the bores to the specified piston clearances. After Randy finished cutting the block, I called Ron with the deck height and the bore diameter.
Before the MP cranks came out, we had to resort to custom cranks that priced most of us out of the small-block stroker market. Now Mopar enthusiasts have an option to go up in cubic inches without a serious downturn in wallet thickness. For about $350 you can get a nodular cast crank from Mopar Performance with four inches of throw, available for all small-block Mopar engines. These are made to fit different variances of the Chrysler small-blocks over the years.
You'll want to determine the components you plan to use ahead of time in order to get the right crank for your application. For example, I chose to go internally balanced with 360 mains in order to utilize the stock 318 harmonic balancer and flywheel. The crankshaft is a nice piece for the money. Knife edges are cast onto the counterweights, followed by shot-peening, then radiusing the fillets during the machining process, and finally chamfering the oil holes and giving the journals a good polishing. The extra holes drilled in the rear flange are a GM pattern. In the end, Diamond's machinist added three pieces of Mallory metal to balance this crank; so plan to have it balanced.
Now a word about the pistons. Diamond offers a lightweight forged piston to use with the 4-inch stroker crank in either 360 or 340 blocks. Your choices vary between a dished (9.5-9.75:1) and flat-top (11.5:1) version for the stroker motors, with both versions carrying deep valve reliefs. I chose the dished version since I planned on using the cast iron heads from my 318. The deck of the piston is still thick, even with the deep valve reliefs. The ring grooves are cut at 11/416-inch, and you can get them with smaller wrist pins. The pistons are a full-floater design, so there will be some upgrades involved in the connecting rod area. These pistons require only .004 inches of clearance to the cylinder bore. The only tricky part is orienting the valve reliefs when you assemble the engine. Since I am using nitrous, I fully massaged the machined edges from around the dish and valve relief areas and filed the piston rings to the gaps specified by the ring manufacturer.