The OEMs haven't put a flat-tappet cam in their engines for 20 years, so why should you? If it were still an affordable way to do things, the cost-conscious OEMs would've stuck with flat tappets forever. The larger the lifter diameter, the faster it can rise up the lobe, so consequently, imaginative racers have been putting bigger lifters in their engines to "cheat" the system for years. Lifter friction, shape, and diameter can all limit the opening rate a cam designer can grind on his lobes for a flat-tappet cam. There are a lot of reasons for this-not the least of which is that flat-tappet lifters can cost you horsepower. Flat tappets are becoming increasingly harder and harder to find, and their prices keep going up. But, they were cheap, and that kept them popular in all circles-until now. And the good-old flat-tappet cams of the past were never the most efficient ways to move a lifter, either. It's much more difficult than you might think. First of all, keep in mind that the cam's lobes are designed to do only one thing: push the lifter up smoothly to open the valve, allowing the lifter to follow the lobe back down to close the valve without bouncing it off the seat. There is actually a lot more to camshafts then we could ever explain in these few pages, so that's why we're going to mostly concentrate on solid roller cams this time.
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