Upgrading the performance of a BMW Si engine

Abstract

This report was prepared at the University of Balamand as a result of research done over a period of two semesters. Our project is divided in two parts. The theory part was accomplished by using software and then the experimental part by working on the engine. The objective of this project is to upgrade a stock SI BMW 6-cylinder in-line, 12-valve engine without using a turbocharger or supercharger, using simulation software and hardware, to study the effects of every part upgraded on engine performance. This operation will lead to raising the horsepower and torque in a safe and cheap way. Before we made any changes, we did many simulations using the "Engine Analyzer Pro" software on many parts with different measurements to find the appropriate ones to get the power needed. To make the engine more powerful, we increased its capacity from 2.5 to 2.8 liter by replacing the original crankshaft, which had a 74 mm stroke, with a crankshaft of 84 mm stroke. In addition, we replaced the original pistons, which have 71 mm length by pistons, which have 53 mm length and different surface form. In addition, we changed the original 249° camshaft by a 324° one. Finally, we used a bigger manifold than the original one, which allowed more air and fuel to enter the engine. Due to these changes, the maximum brake horsepower increased from 167 HP to 273 HP and the maximum brake torque increased from 175ft.lb to 247ft.lb.