The Situation
We are currently in the process of building a 505-inch big-block using a set of Indy EZ heads and the new Mopar Performance cross-ram intake. While we were waiting for some custom parts to be finished, we decided it would be a good idea to toss the cross-ram onto the flow bench and see how well it would-or wouldn't-do. The results had us scratching our heads, so we unboxed a pile of big-block manifolds we had sitting on the shelf and tested several combinations. When the dust settled, we had just about wore out our wrenches by testing twelve different intake manifolds, but we also learned a thing or two that you might find interesting.
Indy EZ heads
All the tests were run with the intake manifolds bolted to one of our new Indy EZ heads. These relatively new heads from Indy Cylinder Head are the answer for engine builders who want to make some serious power while keeping the exhaust ports in the factory location. While most aftermarket heads have the exhaust ports raised for better flow, the guys at Indy figured out how to get a decent exhaust port into a stock location on these heads. These EZ heads can be ordered in several different configurations from Indy, including a standard port version and three different versions that have Max Wedge-size intake ports.
Our heads came from Indy in the standard port configuration, but after some dyno testing last year we sent them off to be CNC ported by Jeff Kobyiski at Modern Cylinder Head (MCH). Jeff is fairly well-known in SS/AA circles as the guy who makes Hemi heads really flow, but he also has CNC porting programs for various wedge heads, including the Indy and Edelbrock parts. The CNC program that Modern Cylinder Head uses for the EZ heads resulted in a finished intake volume of 308 cc and a maximum flow of 351 cfm at .700-inch lift.
Testing Procedure
The first issue we had to deal with was how to mount the cylinder head to our flow bench in order to get repeatable results. We have an older SuperFlow 110 flow bench, which is fairly small, and while it easily accepts a big-block cylinder head, it didn't have any method to properly position the head in a single, precision location. We found if we moved the head around during testing, the intake flow numbers would change as the intake valve was moved towards the center of the cylinder bore. Since we wanted accurate numbers, we came up with a machined plate that has the same dimensions as the deck of an engine block, including the dowel pins that hold the head in the proper location over the cylinder bore.
Once we had the head in the proper location, we ran a quick flow-test of the intake ports on our cylinder head. The first numbers that we came up with were about 305 cfm at .700-inch lift, which was 45 cfm lower than what the flow sheet from MCH showed. We had run these first tests with no inlet radius around the intake port, and the turbulence caused by the sharp edge around the intake port was really hurting the numbers. We knew most head porters use clay around the intake port to smooth out the flow, so we stole some Play-Doh from the kids and built up a little radius around the port. That improved the flow up into the 340-cfm range, and we knew we were on the right path. Since we were working with a CNC port, we figured we would go ahead and machine up a precise flow plate with a full .750-inch radius and try that. Once we fabricated an inlet flow plate with a nice large radius, the head flow picked up to the 351 cfm at .700-inch lift that we were expecting.
The lesson we learned here is that the flow numbers can vary quite a bit depending on how the head is positioned on the bench, and what type of inlet flow plate is used with the head. Those are both potential reasons why the flow numbers on a particular head can vary from bench-to-bench and operator-to-operator.
Flowing the Max Wedge Cross-ram
Once we had the baseline curve for the cylinder head nailed down, we were finally ready to see what flow numbers the big Max Wedge manifold would produce. We were a little shocked to see that the big cross-ram manifold limited the total system flow to 281 cfm, while the bare head would flow 351 cfm. Basically, we were losing 70 cfm of flow capability by bolting the cross-ram manifold onto the head. This was a large enough drop in flow that we began investigating what the flow results would be like with other manifolds in an effort to help us understand the results. All the flow results are listed in the graphs, so we won't go over the details here, but will point out a few of the trends that developed during testing.
The first manifold we tested after the cross-ram was the big 440-2 manifold from Indy. The 440-2 is flanged for a standard 4150 carburetor, and it posted the best numbers when using a 4150 to 4500 adapter as an inlet-flow smoother. The best number posted from this big Indy manifold was 339 cfm, which told us the intake manifold doesn't have to be a big restriction on overall flow. Since there was such a big drop-off from the Indy single plane to the MP cross-ram, we kept investigating other manifolds.
As we tested more and more manifolds with Max Wedge-size ports, we saw a trend develop, with the RB version of the manifolds flowing better than the B engine versions. Evidently the smoother radius of the longer runners on the RB manifolds outweighs any extra wall friction, and the overall numbers are a bit better for the taller manifolds. Also, as one would expect, the single-plane manifolds flow quite a bit better than the dual-plane manifolds.
Once we had tested all the large port manifolds that we had, we went ahead and tested a few standard port manifolds, just in an effort to see what happened to the flow numbers when the port size changes. As you would expect, the manifolds with the smaller ports typically had lower flow numbers than the large port manifolds, but the Victor 440 manifold was an exception to this rule. The standard port Victor actually had better flow numbers than the Max Wedge cross-ram with a difference of 14 cfm at .700-inch lift. Our assumption is that even though the Victor runners are smaller in size than the Max Wedge runners, the Victor runners are shorter so there is less wall friction.
We also dug up some old classic manifolds, such as the Edelbrock DP4B and the CH440, as well as an original '67 440 HP manifold.
None of these old classic manifolds did very well on the flow bench in relationship to newer, updated intakes, but it was still fun to give them a try. These older manifolds will work just fine on a street car, but their day is over for serious street and race applications.
Observations And Conclusions
We learned some basic facts about flow testing that will certainly help us on future projects. The big-block head fixture will come in handy for other projects, as will the nicely machined radius flow plate; now we know how important these tools are in getting good repeatable results.
We're not quite sure how to explain the low flow numbers from the cross-ram manifold, and how those will relate to power output on the engine dyno. We'll be testing this 505-inch motor on the dyno within the next few weeks, and then we'll know if the flow bench numbers predict power output, or if there is more to the story. It does seem logical that the 100-cfm difference between the flow numbers from the '67 HP manifold and the Indy RB manifold are significant. And it would seem perfectly logical there would be a large power difference between those manifolds on a race motor. But the cross-ram design has been a proven performer for many years and works on a different principle than just flow, so we think it might just produce more power than the low flow numbers predict.
We talked about some of the results with Jeff at Modern Cylinder Head, and he pointed out that the flow bench can't replicate the dynamic environment seen inside the intake manifold on a running V-8 engine. He stressed that items such as the runner length, as well as the amount of taper and curvature of the runners, will have a large impact on the power output of the engine combination. flow is important, but it isn't the whole story.
Hopefully, we'll get some answers to these questions once we get this engine on the dyno. We're planning to run the cross-ram as a baseline setup and then swap over to the big Indy single-plane manifold. The flow difference between those two manifolds is almost 60 cfm, which could result in a difference of over 100 hp of output given the standard rule of 2hp-per-cfm of flow. We've already heard from some Max Wedge lovers that the cross-ram will do better than the flow numbers predict, but others tell us that the single plane is the only way to go. Either way, you'll be the first to know the numbers once the dyno session is over.
