Several years ago a handful of Model T enthusiasts started a study of Model T camshafts. We call this study simply The Cam Project. The study was motivated by the frequent observation of low mileage, original Model Tís outperforming those with engines rebuilt using all the latest technology. The grind of the modern camshafts was the suspected cause of the difference in performance.
The first major step in the study was to gather information on the specifications for 26 camshafts. These included two stock T cams, one used prior to 1913 and the one used after, four antique high performance cams, various Model A and B cams, and thirteen of the available reground Model T cams. At the time of the study, no cams were available with a stock grind or any of the antique high performance grinds. Another noticeable difference between these cams is that the stock cams and antique performance cams had an intake valve duration of 225 degrees (seat-to-seat) or less, while the regrinds had an intake valve duration greater than 238 degrees, and more typically about 250 degrees.
Once the camshaft specifications were obtained, an engine simulator was used to calculate the engine performance for each camshaft. The results clearly indicated that the stock and antique performance cams were superior to all of the available regrinds (see Simulation). The modern cams tended to produce less low RPM power and torque.
Chassis dynamometer testing supported the simulation study (see Dyno Testing). Tests were run on a car with a modern cam (264 degrees duration) and again after a NOS (new old stock) cam was installed. The stock cam produced 10 to 15% greater power up to about 1300 RPM and essentially no difference in power above 1400 RPM. With stock gear ratios, 1300 RPM is equivalent to about 32 mph, which is a typical cruising speed for a Model T. With only two gear ratios available, this difference in low-end power is significant, since it helps to avoid the dreaded shift into low gear when climbing hills.
It would appear that Model T enthusiasts have become victims of a very common mistake, i.e. overcaming of the engine. Monroe* states that overcaming is one of the most common mistakes made when building an engine. The duration and lift of the available Model T cams are too large for an engine, which needs to develop power in the range of 500 to 2000 RPM. Monroe states that in order of importance, the six major parameters in a cam design are: (1) intake closing, (2) intake opening, (3) exhaust opening, (4) exhaust closing, (5) intake lift and (6) exhaust lift. Of utmost importance is the intake valve duration, which is determined by the first two parameters. In order to achieve good performance, the valve duration must be compatible with the RPM range of the engine. A low RPM engine like the Model T, should have a much smaller duration than a modern high speed engine. Unfortunately, most Model T enthusiasts appear to be fixated on cam lift, and pay little attention to the other more important factors in the cam design. In order to achieve high lift, many of the available Model T reground cams use a duration which is far too large. Given the relative importance of the various parameters, this approach is completely illogical.
In the Cam Project, we have focused on cams with a duration, which is appropriate for a Model T engine. Although more testing could be done, we are convinced that the ideal intake duration for a Model T cam is in the neighborhood of 218 to 225 degrees. The ideal exhaust duration is in the range of 218 to 245 degrees. If you look at Cam Design, you will find complete documentation of the original stock Model T cam, which has not been available previously. We also describe some of the numerous dimensional constraints imposed on the camshaft designs, and detailed specifications for the three new Model T camshafts. Simulations and dyno testing of the new cams indicate that relative to a stock cam, they will produce a small increase in peak power with essentially no loss in low end power.
*Monroe, Tom: Engine Builders Handbook, HP Books, New York, 1996.