Cam Velocity-Advantage Mopar - Mopar Cam Dyno Jam

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.

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.