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.