The Rotating Assembly
Our plan was to build a short-block that would stay true to the high-compression race flavor of the original Max Wedge, but to use modern parts that are both economical and capable of handling 700 hp. With a little bit of searching, we quickly found a combination of crankshaft, connecting rods, and pistons that gave us 505 ci without breaking the bank.
We talked over the options with several engine builders and learned that many of the big-block stroker motors going together these days are using a 4.250-inch stroke crankshaft with 2.200-inch rod journals. The 2.200 journal is smaller than the stock Mopar journal so the rods weigh less and take up less room. A side benefit is the 2.200 journal works with standard Chevy big-block rods, which tend to be less expensive than the Chrysler rods since they are made in higher volume. The 4.250-inch stroker crankshafts with the 2.200 pins are available from multiple vendors, so availability is good and prices are attractive.
Once we had made the decision to go with the 4.250-inch stroke for the crankshaft, we had to pick a rod length and then find a set of pistons. We wanted a connecting rod that was long enough to keep the piston away from the crankshaft counterweights, but short enough that the piston didn't look like a hockey puck. With a little bit of research, we determined that a rod that was 6.800-inches long would fit all our requirements. The 6.800-inches length is fairly popular in the aftermarket (it was never a factory option), so there were plenty of choices that fit our budget. That 6.800 rod gave us a piston height of 1.790 inches, which is short enough to keep the weight low, but long enough to maintain good stability. We also considered using a 7.100-inches-long rod with a piston that was 1.490 tall, but our decision was made easier when we found out that Diamond Racing was getting ready to introduce a line of shelf pistons that were designed for the 6.800-length connecting rods.
We worked with Diamond Racing on our last stroker buildup and found them to be big Mopar fans. When we talked to them about this project, we found their standard flat-top piston for this 4.250-inch stroke combination would give us a compression ratio of 12.5:1. While that is a nice combination for a bracket motor, we had our heart set on duplicating the original specification of 13.5:1, so we had Diamond whittle out a set of custom pistons with a 6cc flat-top dome on top.
Picking a Camshaft
Once we had the basic parts of the short-block in place, we needed to pick a camshaft profile. One resource we consulted with was Buddy Rawls from Cross Section Engineering. He sent us a detailed questionnaire that covered many aspects of our engine design. Based on our engine parameters, Buddy was then able to provide us with a specific lobe and LCA recommendation. We also talked over the cam choice with Dwayne Porter from Porter Racing Heads. We've used Dwayne in the past as a camshaft sounding board and have always had good success following his recommendations. Interesting enough, those two independent sources provided us with almost identical recommendations, so we felt we were on the right track.
The camshaft we ordered from Comp Cams was a custom, solid flat-tappet design using what Comp calls their SQ lobe family. We went with a number 7265 lobe on the intake and a larger number 7267 lobe for the exhaust. These lobes gave us .300 degrees of duration on the intake and .304 degrees on the exhaust with .600 lift. The cam used in the '63 Max Wedge motor was .300 degrees of duration on both the intake and exhaust side with .509 lift, so our new grind was basically the same duration as the original but with a lot more lift.
Even with this big cam profile, we still had 225 psi of cranking compression. That much cranking pressure told us that we had better run some high-octane race gas, so we filled the tank up with 111 octane Rockett brand race gas. As a point of reference, the original Max Wedge cranking compression specification was listed at 190 psi in the service manual.
We were able to reuse the lifters from our 383 stroker motor since we are using the special Schubeck lifters with the super-hard face material. The Schubeck lifters were just cleaned up and dropped back in on the new cam without any break-in period required.