While rebuilding the 401 V8 from my ’77 Wagoneer, I found that the camshaft it had (which appeared to be aftermarket, since the measured lobe lift was higher than stock on many lobes) was quite worn. Since I had the engine completely torn apart anyway, now was the time to get a new cam.

Choosing a cam can be one of the most critical aspects of engine performance. A cam that’s too “small” won’t allow your engine to reach its full power potential. A cam that’s too “big” won’t idle well (or at all) and won’t accelerate at low RPM. An excellent description on cam theory and how to choose a good cam can be found in David Vizard’s book How to Build Horsepower, Vol I. COMP Cams has provided a good, basic tutorial on valve timing.

The torque converter on my TH400 tranny (non-lockup) stalls at about 1200 RPM, according to the shop that rebuilt my tranny. A stronger engine will increase the stall speed somewhat. Doing a little math told me that my tranny will be spinning 2400 RPM at 60 mph, or 3200 RPM at 80 mph (interstate speed limit is 75 around here). When you figure in roughly 10% torque converter slippage, the engine will be spinning 2640 or 3520 RPM, respectively, when cruising. When accelerating to pass somebody or when towing my Wrangler up a steep hill (8000-lb total vehicle weight), the RPM could be even higher. I therefore decided that a good power range for my cam would be 1500-4500 RPM. Conveniently, this is the exact RPM range provided for most RV/towing cams. FYI, the red line for the rotating assembly in most AMC V8’s is just over 6000 RPM. This cam should cause the valves to float and my engine to lose power long before I’m in danger of throwing a rod.

Stock-ish AMC engines are generally safe using valve lifts of up to .500″ before you have to start worrying about the valves kissing the pistons. The stock 401 cam has .458″ of lift for both intake and exhaust.

The lobe center angle (LCA) determines how much overlap there is between the exhaust and intake openings. A wider LCA provides a wider and flatter (but also somewhat lower) torque curve than a narrower LCA, so I shot for LCA’s of 110 or, preferably, 112 degrees. My calculations show the stock 401 cam as having about 115.8 degrees LCA and the 304/360 having 111 degrees, but that could be wrong (I assumed the lobes were symetric about the centerline).

The final, most critical, and also most advertised specification on a camshaft is the valve-open duration. Based on the RPM range I need and the cam usage descriptions provided by the cam manufacturers, the ideal cam for my application will have around 205 to 215 degrees of duration at .050″ of lobe lift. This translates to about 260-275 degrees of advertised duration. Since there is no standard way of measuring advertised duration, duration @ .050″ lift is the best way to compare cams from different manufacturers. The stock 401 cam has advertised durations of 296 (intake) and 303 (exhaust). Dual-pattern grinds like this, which give more duration and often more lift to the exhaust valves, are not uncommon. I’m unclear as to what their real benefit is, though.

Here, now, are links to my short list of cams to install. I’m leaning heavily toward the Crane H-260-2.

For comparison, here are the stock AMC V8 cam specs taken from my
1977 technical service manual: