Highly Turbocharging a Restricted, Odd Fire, Two Cylinder Small Engine - Design, Lubrication, Tuning and Control

This paper describes the mechanical component design, lubrication, tuning and control aspects of a restricted, odd fire, highly turbocharged (TC) engine for Formula SAE competition. The engine was specifically designed and configured for the purpose, being a twin cylinder inline arrangement with double overhead camshafts and four valves per cylinder. Most of the engine components were specially cast or machined from billets.

A detailed theoretical analysis was completed to determine engine specifications and operating conditions. Results from the analysis indicated a new engine design was necessary to sustain highly TC operation. Dry sump lubrication was implemented after initial oil surge problems were found with the wet sump system during vehicle testing. The design and development of the system is outlined, together with brake performance effects for the varying systems.

Tuning an odd fire engine with an intake restriction and upstream throttle location was explored together with varying injector locations and manifold geometry. To improve engine efficiency, turbocharging and specific engine downsizing were employed in conjunction with a lean burn strategy at low brake mean effective pressure (BMEP). This engine package and tuning strategy resulted in the Melbourne University Formula SAE vehicle being very successful in competition, finishing first in the fuel economy event at the 2004 Australasian competition. Peak BMEP values of 25 bar, believed to be the highest recorded for small engines on pump gasoline were also achieved.