AUTOMOBILE engines, Mr. Rabezzana declares, have reached a point where it is very difficult, by a single improvement, to render any decidedly better performance, adding that, in his opinion, any further worthwhile improvements in engine economy on a conventional engine will be made only by several well-directed moves concerning small details.
He points out that improvements in part-load economy can be obtained by using a homogeneous mixture and efficient ignition.
Multicylinder engines are the ones most affected by low economy at light loads, he maintains, and lists the following as the main disturbing factors inherent in the majority of them: non-uniform mixture distribution among cylinders; low mixture speed in the manifold at light loads; poor turbulence in the cylinder-head; stratification of the mixture; dilution of the mixture due to the valve timing overlapping the high exhaust back-pressure; poor scavenging around the spark-plug gap position; and improper mixture at the spark-plug gap.