All of the aftermarket cam manufacturers build their cams to the middle of the range, under the red color code. If your engine is fitted with any other color-coded cams, you have a couple of options. Most mechanics will tell you that for engines fitted with stock cam gears one size on either side of red—that is, with blue or yellow codes—you can safely use the aftermarket cam without alteration. If this results in the cam gear being slightly loose, you'll likely have some gear noise that sounds like lifter clatter. If it's a bit tight, you'll hear some gear whine. Neither condition should be objectionably loud. For engines fitted by the factory with any of the remaining four color codes, you have two basic options: One is to have a competent machine shop press the gear off your stock cam and onto the aftermarket unit; the other option is to have the aftermarket cam manufacturer do the same thing. All of them will do this work, usually at no extra charge.