The History
We all know the Max Wedge is an all-time classic that roared out of Detroit in 1962. With that big, honking, dual-carb, cross-ram intake, the upswept exhaust manifolds, the radical cam, and the high-compression pistons, the Max Wedge motors made a reputation that has lasted over 40 years. The Max Wedge cranked out 425 hp back in the day when daily-driver motors were barely making half of that, and you'll still find them screaming down the quarter-mile at most any Mopar meet today.
We've wanted to recreate one of these legendary motors for some time, but the special parts required were just a little too expensive for our pocketbook. So when we discovered that Mopar Performance released a reproduction of the original cross-ram intake manifold, we jumped at the chance to finally build our own Max Wedge. Of course, we couldn't leave well enough alone, so while we were at it we made our version bigger and better. By the time we finished, we had 505 inches and 625 hp in our hands.
The Plan
The goal we had was to make a modern version of the '63 Max Wedge. We wanted to maintain the big cross-ram with the dual AFB carbs, the 13.5:1 compression, the Max Wedge ports, and the big flat-tappet cam. But we felt the improvements made in cylinder heads over the last 40 years, as well as the newest options for crankshafts, connecting rods, and pistons, should also be incorporated. So our final plan was the old-school look filled with modern parts.
Our plan for the short-block was to stuff an original RB block with a modern stroker crankshaft since the additional cubic inches is an easy way to make more power. Either a 413 or a 426 block would have been more correct, but we decided to use the more popular 440 block as our foundation. Both the 413 and 426 blocks suffer from a smaller bore size, which really starts to limit the cylinder head breathing. The original Max Wedge engines also need to have notches cut into the cylinder block to provide clearance for the large exhaust valves, but that isn't required when using the larger 440 bore size.
What really made the Max Wedge different from all the other big-block wedge motors was the size of the intake ports. The MW used a super-size intake runner that is almost 30-percent larger than the standard port. These large-port heads were only available from 1962 to 1964, and then that port size disappeared from production. The Max Wedge cylinder head became a legend due to track performance, but since the only intake manifold available was the dual-carb cross-ram, these large port heads didn't really become very popular with the street crowd.
While the factory heads never became popular, the aftermarket recognized a good thing when they saw it. Over time, several vendors, such as Indy Cylinder Head, introduced aluminum heads and intake manifolds based on the large MW port design. The Indy heads differ from the original heads since they have raised intake runners and longer valves, but we felt they were a natural evolution of what the factory engineers started back in 1962, so we chose them for this engine build.
The new intake manifold from Mopar Performance is a fairly close reproduction of the original right down to the lettering and part numbers cast into the top. We couldn't locate a pair of original carburetors since they are few and far between, but once again, the aftermarket has stepped in with a solution. Edelbrock is currently making several new and improved versions of the old Carter carburetor, including a larger 800-cfm model that we decided to run. The throttle linkage on the new Edelbrock carb is a little different than the original Carters, but Mancini Racing carries a special cross-ram linkage kit that fits the Edelbrock carbs. So with that final part in hand, our induction setup was complete.
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.
Indy EZ heads
If you followed the story of our 383 stroker motor, you will be familiar with the CNC-ported Indy EZ heads that we're using here. These heads were ported by Modern Cylinder Head and have a 308cc intake runner with a 3.65 square-inch cross-section. The last motor we had these heads on was 431 ci, and the peak torque with a similar cam was 504 lb-ft at 6,000 rpm. So we were curious to see what would happen on this motor which is about 17-percent larger.
One of the standard formulas for predicting torque peak given the cross sectional area (CSA) of the intake is RPM = CSA * 700,000/CID. In our case, the formula predicts the torque peak will be at 3.65 * 700,000/505 or 5,100 rpm. In comparison, a standard port head has a CSA of only 2.88 square inches, which would result in a torque peak at 4,000 rpm with 505 ci. The moral of the story is that you need to pay attention to the cylinder head volume and cross section when building a stroker or you might end up with a tractor motor rather than a race motor.
On the Dyno
According to the service manual, the power output of the high-compression '63 Max Wedge motor was 425 hp at 5,600 rpm and 480 lb-ft of torque at 4,400 rpm. that was the benchmark we were going to compare ourselves against for our testing.
One thing that had us worried was the carburetor jetting. The original service documentation showed the carburetors should be heavily cross-jetted. For example, the AFB 3705 carb is supposed to be set up with a .089 secondary jet on the throttle side and a .063 jet on the choke side. Our Edelbrock carbs were square jetted with .101 jets on each secondary. So we were 12 jet sizes larger on the throttle side and 38 jet sizes larger on the choke side! That didn't feel correct, but we couldn't find anyone else who had run the Edelbrock carbs on this manifold, so we crossed our fingers and fired up the motor. Much to our surprise, the wide-band sensor told us we were right in the ballpark for average A/F ratio, and the individual cylinder EGT probes showed only moderate differences from cylinder to cylinder.
Since the out-of-box carb jetting appeared to be within a reasonable range, we proceeded to make some full-throttle pulls. The best numbers we recorded over the course of several runs was 625 hp at 6,300 rpm and 610 lb-ft of torque at 5,400 rpm. That gives us a nice 200hp gain over the original Max Wedge motor-not too shabby! No doubt the larger displacement is responsible for a big part of the increase as are the high-flowing Indy heads.
This motor has a nice broad torque curve with more than 500 lb-ft. of torque available from 4,500 rpm to 6,500 rpm, so we're pretty sure it would move a race car down the track in a hurry. In fact, with that big broad torque curve, this combination would actually make a pretty decent street setup if the compression and cam were toned down a bit.
The Indy Cross-Ram adds 80 hp
While we had the motor on the dyno, we decided to do a quick swap over to a cross-ram that Indy Cylinder Head sells. The Indy cross-ram looks like a big box since the runners have been shortened and straightened. The carburetors sit in-line on the Indy manifold rather than being offset, but the runners inside the manifold still crossover the motor from side to side.
We bolted the Indy intake to the 505 motor and swapped the same Edelbrock 800-cfm carbs over from the MP cross-ram without making any jetting changes. The first dyno pulled showed 694 hp, but the A/F ratio was a little lean so we stepped up to 104 jets in the secondaries. The next run showed 705 hp at 6,100 rpm and 640 lb-ft of torque at 5,400 rpm. The jetting was still lean on this final run, but we were out of time with our dyno session. Given a little more time we're pretty sure we could've found a few more ponies by sorting out the jetting. It appears from the EGT readings that the carbs would need some cross-jetting to get the cylinders all running the same temperature.
Wrap up
So there you have it. The Mopar Performance reproduction manifold will easily crank out more than 600 hp and 600 lb-ft of torque when bolted to some modern heads on a big-inch short-block. And if you don't limit yourself to the factory intake, you can easily move up to the 700hp neighborhood with just a quick swap over to the Indy cross-ram. You just have to love how easy it is to make big power these days with the stroker kits and heads that are available for the venerable big-block Mopar.
