From the J&P Cycles Blog Archive

Trying to select a cam can be frustrating and downright confusing, so let’s see if I can shine some light on the frequently asked question, “What cam is right for me?” Hopefully I can answer this question and at the same time give you the knowledge to know what you are talking about when it comes time to select and buy your cam.

Obviously there are several factors that need to be looked at when talking about power. Head design, valve size, stroke, compression ratio, carburetion, ignition and exhaust all add up to create horsepower and torque in addition to the cam. But for now, we will just talk some cam tech.

A lot of the more popular cams you hear about out there may not be the right cam for the kind of bike you have, or the style of riding you do. For instance, if you ride a bagger and tote the wife with you, or if you ride your bike in town and do a lot of stop-and-go riding, you want a cam that will give you more low-end torque. If you have a light bike like a Dyna or FXR, a midrange power cam will give you a lot of top end power.

If sending your motorcycle to a machine shop, buying all the special tools, or one of the many other engine modifications that it takes to run some cams isn’t in your budget or know-how, there are some bolt-in cams that you can go with. Keep in mind that I say the words “bolt-in” loosely. This doesn’t mean you can pop the cam cover off and just throw it in. There are some minor checks you need to do and your service manual can walk you through them. Otherwise, a quick call to the J&P Tech Support line would be good. We are always willing to lend a helping hand. Also remember that if you decide to go with a bolt-in, it would not be a bad idea (but not necessary) to add a set of less restrictive exhaust pipes. Do a little re-jet on the carb and give the ‘old gal a high-flow air cleaner. All that being said, let’s look at a couple of factors you will need to know when looking for your cam.

Camshafts with duration under 250 degrees and lift below .500 inches of lift can be considered bolt-in cams. (Cams with over .500 inches of lift and over 250 degrees of duration require hop-up compression and heads to work best.)

By installing a cam, you can expect certain power gains in certain areas such as low end, midrange and top end. To achieve that, we use the cam to manipulate or tell the valves what to do. The cam tells the valves what to do through the “valve train.” (Cam to lifter, lifter to pushrod, pushrod to rocker, and rocker to valve.)

The amount of time the valve is told to stay open is the duration we talked about. The higher the duration, the more air/fuel mixture is allowed into the combustion chamber. The cam also tells the valves how far to open (off its valve seat on the head) to achieve the same effect. This is the degree of lift we talked about.

As a general rule cams that have 220-235 degrees of duration produce good low-end torque. Motorcycle cams with 235-250 degrees of duration work well for midrange and cams with over 260 degrees work best for top end power.

Many manufacturers make bolt-in cams that perform. Remember that there are many other ways and combinations of things you can add to achieve power gains. The cam is but one part of the vast power spectrum. Don’t think that by throwing in a bolt-in cam, adding a carb and a set of pipes that you are going to turn your bike into a pavement eating 100 hp monster. Getting that stock 80 to throw 100 hp at the rear wheel takes a lot of time and money, but a well-tuned engine combination of a bolt-in cam, a decent exhaust, and a little carb ticklin’ is very capable of smokin’ your buddy’s off the line.