Solid-roller cams demand stability...
Solid-roller cams demand stability on the pushrod end of things, which is why they chose these superbad dual-taper pushrods from Trend. Lightweight components on the valve end of things evens out the formula.
They used a Milodon adjustable gear drive to motivate the cam and were pleased with how much it helped in terms of being able to make changes quickly. "It was a beautiful thing for quickly indexing the cam on the dyno-just to see how much that moved the curves around. Lo and behold, like everyone else, we found that we seemed to have the best averages when we kept advancing it, pretty much until we ran out of positions. It was really eye opening at how convenient the gear drive made that."
Another weapon available to the team was a pair of Edelbrock Victor cylinder heads. The big "E" is known for having exceptional castings and leaving nothing on the table when it comes to quality components. "I had never used the Victor heads before so it was kind of a learning curve." Using a SuperFlow SF1020 flowbench as his guide, Robinson spent countless hours sizing the ports and finessing the curves in the heads. He had a target minimum crosssectional area (MCSA) that he was shooting for to get the flow numbers that he wanted while keeping the runners high and tight. That combination makes for ports that build a ton of velocity quickly in the rpm range and add to the torque curve. It is a fine line that experts like Robinson tread between building velocity and making the runners so small that they won't let the engine build power up top. Experience, science, and art all combine to make it happen correctly. "I measured a lot, but I was very concerned with pushrod clearance because every time I opened the intake ports at the pushrod pinch or the flange, flow would pick up quite a bit but I felt I was running out of pushrod room and I didn't want to make a hole." Regarding how the stock style big-block heads are located on top of the cylinders, Robinson let us in on a little secret: "In the past I've actually reverse angle milled them with great success. I thought about doing that, but to be honest, time just ran out."
A little detonation down low...
A little detonation down low put the Mahle/Clevite rod bearings to the test but they passed with flying colors. The pistons are a basic enough shelf stock design that anyone can buy to repeat this combination.
The open chamber design of the Victor heads was only modified to the extent that the intake side was laid back a touch. That modification was not only good for flow but placed the fuel mixture more evenly in the chamber for a good burn.
"I used a 5/16-inch stemmed Ferrea valve on the intake side and I experimented with a 50-degree seat, but I just couldn't get it to work with that port and chamber configuration so I abandoned that and went back to a 45-degree seat. We actually went from 2.3-inch back down to 2 1/4-inch valves where I got my best results." The lightweight valves also allowed them to run lower spring pressures and cut some frictional losses. Since the Victor heads were designed as a true bolt-on, they used a 1.880-inch spring height which slightly limited the amount of lift they could run with the available springs. Even so, the guys were able to get a solid three quarter inch of lift!
SKMFX team members Ron Maclean,...
SKMFX team members Ron Maclean, Joe Rutters, and Jesse Robinson were proud of their Commando in black, and were relieved that they didn't have to declare this WMD as they crossed the border back to their homeland of Canada.
To the chagrin of the Blue Oval and Brand X camps, Mopar designed its engines with shaft rockers from the factory. T&D Machine built the rockers for the SKMFX engine, and they fit perfectly on the Eddy heads. For years some complained that aftermarket big-block shaft rockers had problems with the aluminum side spacers locking up when the engine was hot and creating a condition similar to valve float. The aluminum locators would expand and sandwich the rocker arms where they couldn't move. T&D addressed this by making their lateral locators from a composite material. Robinson said their rockers worked perfectly.
Since the Challenge was fairly open as far as intake manifold rules, Robinson's team went for the kill and chose a Weiand tunnel ram. Careful searching on eBay led them to their quarry where they were able to pick up their intake for pennies on the dollar. The used manifold and the engine block were toted over to the SKM powdercoating shop for a slick black finish. Naturally the valve covers were treated to the traditional Mopar wrinkle finish but with the SKMFX logo CNC machined in the top.