Specification (spec) race engines are intended to reduce costs and increase the competitiveness in many racing classes. However, engines prepared by the best race engine builders routinely outperform truly ‘standard’ engines or engines prepared by less experienced tuners. This paper describes how engines can be modified to increase their power output and discusses various spec engine preparation techniques. Experimental and computational evidence is used to quantify the potential benefits that can be expected from each of the modifications discussed. By combining several relatively small improvements, a well prepared engine may be expected to enjoy a 5-8 % power benefit over an ‘average’ race engine, and perhaps as much as a 14-17 % benefit in power versus a truly standard production engine off the assembly line. This analysis also reveals the claims of much larger power improvements by some high-performance engine tuners can not be substantiated unless further modifications are made.