Using a Hughes cam with lobes designed for the large .904 Mopar lifter diameter, this str
Pick up any camshaft and it's pretty simple to see what it does. It turns, the little bumps come around and move the lifters, which-through the pushrods and rockers-open the valves. The truth is, there is no part of an engine's design as complex as that simple-looking bump on a camshaft. The trend in current cam design is to accelerate the valve more quickly off the seat and open the valve at a higher velocity than older cam designs. This results in more lift for a given amount of duration, which, in turn, offers better low-end performance and torque production for a given level of top-end power output. The limiting factor in how much velocity can be designed into a flat-tappet cam is the diameter of the lifter.
For example, if your lifter's diameter is comparable to that of a 55-gallon drum, it's not hard to imagine a monster camshaft lobe which could lift it a foot or more off the ground. On the other hand, if the lifter is the diameter of a pencil eraser, a similarly matched cam under it would be able to move it only a fraction of an inch without it binding on the lifter edges. These are extremes, but it doesn't take a huge difference in lifter diameter to make a significant difference in the velocity designed into a cam lobe. Mopar engines had relatively large 0.904-inch-diameter lifters from the factory, while Chevy small-blocks came with puny 0.842-inch lifters. So who cares about the size of a Chevy lifter? We hate to say it, but cam grinders do. Typical aftermarket cam lobes are designed to work with a Chevy-sized minimum tappet diameter of 0.842 inch, since a lobe designed for the smallest lifter will work in any engine with a lifter that size or larger. These lobe designs are transferred to masters on cam grinding machines, and the lobe is duplicated onto cam blanks, be it a Ford, a Chevy, a Mopar or an International. Sure, these "Chevy" lobes work well and make horsepower, but the potential advantage of the larger Mopar lifter is left untapped.
Steve Brule, the dyno operator at Westech, already had the 440 mounted to the Superflow 90
Luckily, there are a few cam grinders out there that have developed lobe profiles designed to take advantage of the higher velocity possible with Mopar's larger lifters. These 0.904-inch minimum tappet diameter lobes won't work with the smaller 0.842-inch Chevy lifters, or even Ford's 0.875-inch tappets, without the camshaft lobe catching the edge of the lifter. How much of a difference is there? That depends on how aggressively the lobe is designed, but a typical "Chevy" flat-tappet performance grind with 230-degree duration at .050 inch can deliver 0.480-inch lift at the valve with a 1.5:1 rocker. A lobe with the same 230-degree duration at .050 inch designed to take advantage of the higher velocity possible with a Mopar's 0.904-inch lifter will provide 0.515-inch valve lift. Hey, I'll take an extra .035-inch lift for the same duration any time!
It's true that just going up in duration, say to a 240-degree at .050-inch cam with a "Chevy" lobe, will bring that lift up to the 230-degree Mopar lobe's level. However, having to step up in duration has its price. Going up another size in cam will add to top-end power, but driveability and low-speed response will typically suffer. In theory, the timing of the valve events has more to do with the engine's idle quality and low rpm cylinder pressure than the max-lift figure. Put another way, duration and lobe separation specs will have the greatest effect on the idle quality and low-end power achieved with a selected cam. Therefore, if more lift can be built into a cam with otherwise the same specs, the potential is there to make more power, without giving up much, if anything, in terms of driveability and low-end output.