Measured Power and Torque

Several members of the Tulsa Club (Fred Houston, Mike Bender, Bill Gent and Larry Young) recently tested several heads on a chassis dynamometer in Oklahoma City (see photos).  We tested a stock high head, a Waukesha-Ricardo head, a Riley Multi-Ford head and a Z head.  The Waukesha-Ricardo and Z heads were both milled 0.050 inches to reduce the clearance over the piston to 0.060 inches.  This modification produces a small increase in the compression ratio.  Modifications to the Riley head are unknown.  For these tests we used Larry Young's 1926 Tudor, which was used in all of the camshaft testing (see Dyno Results).  The only change to this car since previous tests were the installation of a Bosch 600 with a Pertronix Ignitor (see Distributors).   The dynamometer used in these tests was a different type from the one used previously, and is reported to produce somewhat smaller power and torque numbers.  Compared to our expectations from the previous tests, the peak torque numbers were in line with our expectations, whereas the peak horsepower numbers were about 10 percent less than we expected.  In order to compare performance numbers, the same dynamometer must be used.  Two runs were made with each head and in all cases the second run gave slightly better performance. 

The power and torque values are shown in the graphs below.  The results tend to correlate with the compression ratio of the head.  As one would expect, increased compression gives improved power and torque for all engine speeds.  Compared to the stock head, the Waukesha-Ricardo head produces a 14 percent increase in peak power and a 9 percent increase in peak torque.  The performance of the Riley and Z heads are virtually identical.  Each produces about a 42 percent increase in peak power and a 30 percent increase in peak torque.  These results are consistent with our previous dynamometer results, where we found that the Z head produced 45 percent greater horsepower and 33 percent more torque.  

The performance increases for all of these heads is more than one would expect from compression ratio alone.  For example, the graph "Theoretical Peak Power" suggests that a compression ratio of 4.2:1 should produce only a 6 percent increase in power, whereas the Waukesha-Ricardo head produced a 14 percent power increase.  A 5.7:1 compression ratio would theoretically produce a 25 percent power increase, and yet the Z head and Riley head produced a 42 percent power increase.  The greater than theoretical power from these heads is evidently due to their improved combustion chamber design.

We also tried to test the Green Engineering head, but encountered a near catastrophe due to the valves hitting the top of the head.  Luckily, the valves were wedged open and the car would not start.  This head would have to be modified in order to run a 280 cam and Chevy valves.

Tom Carnegie has recently tested several Model T heads on an engine dynamometer. The results of these tests are shown in the figures below. Performance curves for the 1918 tests made by Ford Motor Company (black lines labeled "Ford") are included for comparison. These results indicate that the Waukesha-Ricardo head has the best low end performance, while the Z head has the best performance at higher RPM. In fact, a Z head was found to be no better than a stock head below 900 RPM. These results conflict with our own experience.