Dave Stribling
March 2, 2016

What Cam Is It?

Can you tell me where I can take my cam and find out if it is the solid lifter cam that came in my Boss 302? I mixed it up with a hydraulic I was using and want to be sure I don’t damage my engine. I got my heads back from the machine shop and want to use my springs. If I have to, I’ll get another cam with no more than 0.290-inch lobe lift, as all the cam companies use the 1.6:1 rocker ratio and most are too much for my stock springs.

Marty Schill
Via the internet

Figuring out which cam is the original for the Boss 302 is easy. It is marked “AEX” with the A upside-down. This mark is located at the end of the camshaft, and a Ford logo is stamped 180 degrees on the other side of this mark. The end farthest from the timing chain also has a white paint daub. The Boss 302 camshaft specs are 0.290-inch lift, 290 degrees duration. The factory yield with stock 1.73:1 rockers is about 0.501 inch, less valve lash. With your 1.6 rockers your lift will be 0.464 inch. The stock rockers will lift the valve more than the aftermarket rockers. If you are running the stock valve springs you should be OK, but have your engine guy check.

Checking the lobe lift on your camshaft is very easy. If you have an inexpensive set of dial calipers, you can measure the camshaft base circle against the lobe lift and get a fairly accurate number. The base circle is the smallest part of the egg-shaped cam lobe, and the lobe lift is the additional amount at the top of the egg-shaped lobe. The example I have here is a Ford Racing Z303 hydraulic roller cam. I measured the lobe base at 1.330 inches (image 1) and the lobe lift at 1.675 inches (image 2). Subtract the base from the lift and you get 0.345 inch. Now multiply this number by your rocker ratio (stock 5.0L rockers are 1.6:1) and viola! You get 0.552 inch of lift, just as Ford advertises.

Camshaft duration is a little harder to measure easily, as it deals with the number of degrees of rotation of the crankshaft, not the camshaft. It can be measured, but you can get your Boss cam picked out by checking the lobe lift minus the base circle at 0.290 inch of lift.

The base circle on a camshaft is the smallest diameter of the lobe before it starts rising.
The lobe lift is the additional rise in the lobe that lifts the camshaft lifter. Subtract the lobe lift from the lobe circle and you get the lift of the camshaft. Multiply this number by the rocker arm ratio and you get the total lift of the camshaft.
The end of an original Boss 302 camshaft will be marked “AEX,” with the A upside-down (highlight for clarity). The opposite side of the camshaft will have the Ford logo. There will also be a white stripe on the end. Special thanks to the Cunningham Archives.