Only ten years ago the two-stroke engine was widely and quite understandably thought to be a reasonable alternative to the four-stroke only when minimum weight and manufacturing cost were all-important considerations. The two-stroke was recognized as having substantial theoretical promise, as it delivered a power stroke for each 360 degrees of crankshaft rotation but the hard reality was that each individual power impulse was too feeble to amount to much when totalled at the output end of the crankshaft. A very few engines had begun to appear in which some of the theoretical promise was realized however, and this encouraged engineers at MZ, Yamaha and Suzuki to persist in their efforts to wring competitive power output from the racing two-stroke engine. To say that they were ultimately successful would be gross understatement.

Those engineers were motivated by the need to demonstrate that the two-stroke engine, per se, was worthwhile — as that would stimulate sales of their companies' ordinary touring models. My own interest in the two-stroke, which had reached the level of an obsession by 1963, was generated by comparative poverty. I like to tinker with engines, and the complexities of the poppet-valve four-stroke make modifications very expensive. One may think that a change in valve timing wold do wonders for a four-stroke’s power, but getting a camshaft made to order costs hundreds of dollars. In contrast, a two-stroke engine’s valve timing may be altered

simply by reshaping the holes in its cylinders, and its power output markedly changed by utilizing inertia and resonant effects in its intake and exhaust tracts. None of these modifications are costly.

On the other hand, while the two-stroke engine does not commonly require large dollar inputs to raise its power output, it does require an in-depth understanding on the part of the man doing the modifications. In an attempt to acquire that understanding I began a study of the high-speed, high-output two-stroke engine that has led to the collection of a minor library of text books and SAE papers. And to an endless series of experiments, some of them illuminating and many others raising more questions than they have answered. At this stage I have arrived at more or less satisfactory explanations for most of the gross phenomena, such as the general behavior of expansion chambers and port time-area values, and 1 flatter myself to think that Just that much is an acceptable excuse for writing this book for the guidance of the layman experimenter. If it will not supply all of the answers it will at least take care of the fundamental problems and prevent the worst mistakes.

My special thanks to Mr. John Brooks, of McCulloch Engineering, who has done much to dilute my once pure ignorance (but should not be held accountable for the residue found herein). Also to the late Henry Koepke, who mistakenly assumed that I knew something about two-stroke engines and supported my early research; to my old friend Joe Parkhurst, who started me working on this book nearly ten years ago but never got it; and finally to Tom Heininger, who wheedled, needled pleaded, complained and cajoled until I hammered my file of notes into publishable form.