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UJOlrll ... Since the da ys when Chrysler engineers intro­duced the industry's first generation of mod­ern, high-compression engines, they have made engine improvement a continuing program. Each year we see new refinements which make our engines more efficient and longer-lasting.

Generally speaking, engine improvements are gradua l and stem from the availability of better fuels, engine materials and manufacturing processes. Many changes in materials and dimensions are made without fan fare because they do not affect service procedures. H owever, the accumulation of these improvements has given us sturdier, more efficient engines than we had only a few years ago.

Actually, we've been servicing the latest gen­eration of engines s ince the middle 1950's. Higher octane fuels, improved lubricants, bet­ter bearings, and generally stronger engine parts have permitted the engineers to substan­tially ra ise the compression pressures and power output of these engines. But, as you might expect , such engine improvements a lso require si.m ilar improvement in servicing prac­tices. For example, the t rend toward h igher operating pressures and stresses makes the need for accurate settings and service adjustmen ts more critical than ever before.

Tech had all this in mind when he suggested the subject for this session. He felt that all Master Technicians would better understand the importance of precise servicing adjust­ments if we took a close look at the complete combustion process in a typical engine of today.

To help in our explanation, we'll first review the basic combustion process by going through the four-stroke cycle. Then, we'll describe the changes in fuel mixture and ignition timing which normally occur under different engine operating conditions.

TABLE OF CONTENTS:

INTRODUCTION .................... . . . ... .. . 1 HIGH COMPRESSION COMBUSTION ............ 2 FULL-RANGE M IXTURE ANO TIMING EFFECTS .... 9