The car used in this test was the same 1926 Tudor sedan, which previously received a NOS cam in place of a long duration regrind (see Stock vs Regrind).  Here we swapped the NOS cam for a new 280 Super-Power cam.  During the one and a half year period between the two cam swaps the car was driven about 2000 miles.  Total mileage on the engine at the time of this second swap was about 4000 miles.  During the interim period between the two cam swaps, the car was modified with the addition of a high compression head (a Z head) and modern bearings throughout the drive train (from Stoltz).  Other than these modifications the car was completely stock.

Before the cam swap the car was dyno tested using both a commercial dynamometer and our Cheapo Dyno.  You may download Cheapo Dyno for free.  The results from these two tests are shown below.

The commercial dynamometer gives greater horsepower and torque at low engine speeds.  This trend was observed in previous tests, and we have no explanation for the difference.  However, since both methods are self consistent, either can be used for comparing camshafts.  The chassis dyno is probably somewhat more precise, but Cheapo Dyno uses measurements from the actual acceleration of the car.  As with previous tests, both methods will give fluctuations in the results from one run to the next.  Differences of less than one half horsepower are not considered significant.

Comparing this figure with the previous results (see Stock vs Regrind) shows the improvements achieved by the installation of the high compression head and modern drive train components.  The peak power increased by a dramatic 7 hp or 45%.  At 1000 RPM the power and torque increased by 33%.  The Z head is advertised to produce a compression ratio of 6:1 and a power increase of 35%.  However, we found that the head produces a compression ratio of only 5.3:1 (see Heads for additional technical information).  Our Z head was milled 0.050 to reduce the squish space over the pistons to 0.060 inch.  This also increased the compression ratio to about 5.7:1.  Increasing the compression ratio from stock (3.8:1) to 5.7:1 will theoretically produce a 23% increase in power.¹  

At first we thought the 45% power increase could not all be attributed to the head, and possibly some of the increase was due to reductions in drive train friction losses.  However, a year later (see Heads) we retested the car with the stock head and found the high compression head gave a 30% increase in torque and a 42% increase in horsepower.  This result suggests that the drive train components contributed very little to the increase and that the Z head achieves a significant portion of its power increase from improved combustion chamber design.

These performance improvements are in addition to the almost 15% increase in low-end power obtained by swapping the reground cam for a NOS cam.  The installation of the NOS cam, Z head and modified drive train resulted in a 54% increase in power at 1000 RPM and a 45% increase in peak power.  The dyno results confirm our seat-of-the-pants appraisal that the car was running extremely well - an opinion confirmed by those that have driven behind it on tour (see testimonial by Becky Bell and Hill Climb Results).  These improvements are truly wonderful, especially when one considers that the car is completely stock except for the head and drive train, and unlike the addition of distributors or modern carburetors, these changes do not alter its appearance and unique features. 

All of the research in this project has shown that an unworn stock Model T cam is an excellent cam.  Unfortunately, after 75+ years of use, there are not many unworn stock cams around.  If you have one, you should use it and consider yourself truly fortunate.  The new cams were introduced to provide a source of good replacement cams. For the three new cams, the simulator predicts an increase in peak power of only 3 to 12% relative to a stock cam, with little to no loss in low end power (see Simulation/New Cams).  The only reason for swapping the NOS cam for 280 Super-Power cam was to confirm that we have designed a cam which is at least as good as a stock cam, with perhaps a small increase in peak performance.

The basic procedure for swapping cams is the same as that described in the Model T maintenance manual (the blue book that used to be green).  This procedure was followed to install the 280 cam.  The NOS cam, which we removed had the later style short front bearing, so we used a new babbit long front bearing for the 280 cam.   In our case, modern keepers and adjustable lifters (Bob's 3 wrench lifters) were installed when the engine was rebuilt.  The base circle radius of the exhaust lobe on the 280 cam is slightly smaller than a stock cam, while the intake base circle is about 0.050 larger.  Since we did not have the necessary adjustment available with the lifters, about 1/32 inches was ground from the stems of the intake valves.  This caused the keepers to extend beyond the end of the valve stems.  This problem was easily fixed by using keepers that sit further from the end of the valve stem.  This problem could also be fixed by turning a new groove further up the valve stem.

There has been some concern about the lifters (Bob's lifters) interfering with the travel of the intake lobes.  On the 280 cam, the distance from the center of the shaft to the tip of the intake lobe is 0.081 greater than for a stock cam.  The lifter must be able to rise this additional distance.  These lifters have a taper near the foot which may prevent this additional travel on some blocks.  On our 1926 block, we found no problems with the lifters.  There was easily 0.050  inches of travel beyond that needed for the 280 cam.  It is possible that a problem could occur for other blocks.  If so, the only solutions are to switch to the improved stock grind, switch to different lifters, or remove some material from the block.

The valve clearance on the new cam was set at 0.010 in accordance with the specifications.  We made the mistake of setting the clearance after the valve springs were installed.  With springs installed, the valve clearance is difficult to set with 3 wrench lifters, because the valve must be up to adjust the lifters, but it must be down to measure the clearance.  Since these are new precision ground cams, the clearance was set using a dial indicator on the top of the valves, and by adjusting the lifter until the maximum lift was 0.270.  Spot checks of a few of the valves showed that the clearance was indeed 0.010.  We also performed a few checks with the "Freebie Degree Wheel" from the Montana 500 website.  Although this is a fairly crude degree wheel, we found that the cam centerlines and the durations were all within about one degree of the specifications

During the swap, we found a considerable amount of carbon in the combustion chamber and asphalt-like deposits on the underside of the intake valves.  This was surprising, since the car had only been driven about 2,000 miles since the previous cam swap.  The carbon and deposits were removed.  However, we do not know how this removal may have effected the cam comparison.

Once the cam swap was completed, we found that the car was not running smoothly.  It was sputtering, occasionally missing, and did not feel like it was making full power.  After some work on the ignition system we obtained the following dyno test results.  Each of the Cheapo Dyno results are an average of the best four runs.  The chassis dyno results are an average of three runs.

We could not detect much difference between the magneto and battery by our seat-of-the-pants appraisal.  It felt like the car produced a little more power on the magneto, but it was smoother with a 12 volt (or in some cases 18 volt) battery.  However, the dyno indicated better power was produced by the battery.  After recharging the magnets, chassis dyno runs were made with both battery and magneto ignition.  The peak power was about the same with both, but the battery produced smoother power curves (show above).  All of the runs with the stock cam were run on magneto, which seemed to produce good, smooth power.  It is too late to run the stock cam on battery power. Due to the troubles with the ignition system, it is difficult to make strong conclusions from the results.  It is clear that the 280 cam produces at least as much power as the stock cam, but the dyno tests do not clearly show that it produces more.  The dyno tests indicate an increase in peak power of from zero to 5% and the peak torque is essentially the same.  The simulator indicated that the peak power should increase by about 7% with a slight loss of peak torque (see Simulation/New Cams).  These differences are apparently too small to measure in a test of this type.

In retrospect, it would have been better to run all of these tests with a distributor rather than the quirky and temperamental stock ignition system.  Although I have no desire to permanently run the car on a distributor, performing the tests with one would allow us to concentrate on the performance of the camshaft.  We will consider the use of a distributor in future tests.

To go with these tests, here is some anecdotal performance data.  The top speed of the car appears to have increased from about 49-50 mph up to 50-51 mph.  The discussion of Power and Torque indicates that it would take about an 8% power increase to achieve a one mph increase in speed.  I also found that the car can now climb the Chandler Park Hill in high gear (see Testimonials) - a feat I have been trying to achieve for more than 10 years.  If you are familiar with this hill, you can appreciate the difficulty of this challenge, especially with a heavy sedan.  After installation of NOS cam, Z head and drive train bearings, I made one unsuccessful attempt to climb the hill in high, but this took place some time ago.  Based on the dyno results, I suspect that on a good day, it would pull the hill with the the stock cam too.

References

¹ Roger Huntington, "Souping the Stock Engine", pp 67-68, Fisher Books, 1950

² Milt Webb and Carl Amundson in Vintage Ford Vol. 12, No. 3, p.43.

³ Bill Cannon, "Effects of Rear Axle Ratio on Antique Car Performance - Part 1", Skinned Knuckles, vol. 25, no. 2, Sept. 2000.   Data originally from Yale Univ. published in "Internal Combustion Engines," by Robert L. Streeter and Lester Clyde Lichty, McGraw-Hill Book Co., New York, 1929, p. 271