T Camshafts Testing, Part 2 

Test Method Details

Several years ago, I began working on a book on Model T Speedsters. One of the things I wanted in the book were performance comparisons of T Speed equipment, especially OHV heads. The rarity of Model T Speed Equipment these days makes it very difficult to assemble and dynamometer test engines with various configurations of T Speed equipment. Of course, the second problem is finding an engine dynamometer. After reading about how drag racers were predicting engine performance using computerized engine simulators, I began to think that maybe I could do the same with the Model T engine.

I learned of an inexpensive engine simulator program and told my wife about it. My wife is very good at picking up on hints, so at Christmas (1996) I found the simulator all wrapped up under the tree. Several weeks later I mentioned to Fred Houston that I had this program and what I wanted to do with it. He thought that was a great idea and wanted me to immediately do a comparison of Model T camshafts. He announced with great enthusiasm "We must do cams!" Over the next few days I worked with the simulator and discovered that it would not record data below 2000 rpm. Also, it would not accept the stock Model T cam timing. It was clear that the program might be useful in simulating a hot OHV engine, but it wouldn’t simulate a stock Model T at 1600 rpm.

Fred was disappointed when I told him about the problems with the simulator. I put the program away. I felt it could not be used to 'do cams', but that it still might be useful when I write the engine chapter of the book. A few months later I got an enthusiastic phone call from Fred telling me he had "Found the answer to my cam problem!" At this point, I knew my fate was sign, sealed and delivered. Fred’s ‘cam problem’ was also my ‘cam problem’ and I was about to help him solve it!

I’ve known Fred about 20 years and know that he doesn’t give up easily on a problem. I didn’t realize at Christmas time just how fired up Fred was about finding a way to compare cams. After talking with me he began telling everyone he knew that they had to find a way to test cams. It seems that Terry Shaffer, a mutual friend of both Fred and I, had found another simulator program that they thought would simulate the Model T engine. Terry bought a copy, and he and Fred began experimenting with it. After their initial experiments they decided this simulator would work, and that I could use it to solve ‘my cam problem.' So, before the phone conversation was over I had resigned myself to "doing cams" for the next few months.

The first step was to collect data on Model T and Model A cams (a Model A cam can be modified to fit into a T and is a good option if running an OHV head). I soon discovered that nearly all the cam timing data available was given in 'seat to seat' measurements. The simulator program required that the cam timing data be in .050 inches measurements. Luckily, one of the cams I had researched had the timing events listed in both types of measurements. I found that I could calculate the .050 inch measurements by subtracting 11 degrees from the opening and closing events in "seat to seat" measurements. Using this information I converted all the cam information to .050 inch measurements. It is likely that this conversion has introduced some error into the timing events of some of the cams. If the acceleration ramp angle of a cam being converted is different from the cam I had dual measurements for, then subtracting 11 degrees would not be correct. However, I do not think the amount of error is significant.

By this time you are probably wondering what the heck is 'seat to seat' and .050 inch' measurements. "Seat to seat" means the timing event beginning and end is being measured when the valve begins to move from the valve seat until it rests on the seat again. Unfortunately there are no universal ‘seat to seat’ measuring standards. Cam manufacturers were using different measuring standards when advertising their cams. This meant that it was very difficult to compare cams, and was causing much confusion among cam buyers. To clear up some of this confusion the cam manufacturers established a new standard of publishing cam timing data. The new standard requires that the crankshaft degrees listed for valve open and closing events be stated when the valve is .050 inches above the seat.

In 1919 Ford published in the Service Bulletins horsepower and torque curves for the stock Model T engine. The text published with the curves implies that the curves were created from an engine dynamometer test. I decided that I should try to duplicate these curves using the simulator software. I felt that duplicating these curves using the stock cam would add some validity to any curves generated using different cams. After carefully entering all the required engine data, I made the first run with the simulator. The curves were within one percent of the originals from 1500 to 2000 rpm. However at 500 rpm both curves were about 40% higher than the 1919 curves. After some discussion with Fred, we decided that the only thing that would effect horsepower and torque equally was internal friction. We felt that the simulator was not accurately calculating the internal friction caused by the heavy planetary transmission, and flywheel magneto assembly (You must remember that this simulator was designed to simulate modern engines with just a light flywheel). We think the internal friction of a Model T engine decreases as rpm rises to 1500 rpm then begins to increase at about the same rate as a modern engine. We think the internal friction decreases as the oil in and around the transmission is thrown out to the sides of the hogshead by centrifugal force.

To fix this problem I entered the results from the simulator into a Lotus 123 Spreadsheet Program. In the spreadsheet, I wrote a program that increased the internal friction in the lower rpm range until the simulator curves matched the 1919 curves. All the torque and horsepower numbers shown have been adjusted as outlined above.

Because of the assumptions and adjustments required it is unlikely that an actual engine dynamometer test would exactly match the results from the simulator. In actual practice, it is almost impossible to get the same results from different dyno tests of the same engine. However, it is important to note that the simulator tests were run with exactly the same configuration except for cam timing and cam lift. Any differences in performance can only result from differences in the cams. Although a dyno test may not produce exactly the same numbers as the simulator, the differences in performance trends between cams should be similar. While comparing the simulator results with an actual dyno run would be interesting, it is not critically important. Because it is so much easier to control the variables that affect performance on the simulator, I think the simulator does a better job than the dynamometer of showing the subtle differences between cams.

The tables under the buttons at the left are the horsepower and torque results for the 26 cams tested in each of the four different engine configurations.