How to build a High Performance Shovelhead Engine

The following information for building a high performance Shovelhead engine was discovered in the archives of a Harley-Davidson dealership.  The list of modifications has been attributed to the HD Engineering Group responsible for XR-750 development in the late 70's or early 80's. While it is probably not possible to validate this claim, some of the ideas presented in the modification list are very interesting. Many of the recommend modifications are closely aligned with performance work being done in the 90's, not 1970's technology as practiced by many Shovelhead mechanics.

This does lead us to the conclusion that the originator of this document was familiar with advances in air flow technology as practiced by engine developers like Colin Chapman (Lotus Formula 1 racing, Cosworth Engineering) in the 60's. It is an interesting footnote that the concept of high velocity port design did not make it to mainstream Harley-Davidson performance engine modifications until the mid to late 90's. This Shovelhead modification document distinctly shows "D" shaped ports, optimized for high velocity over the more popular "bigger is better" philosophy that was used then, and unfortunately is still used today.

At least one Shovel engine has been built using many of the ideas present here, with excellent results. As a favor to the Shovelhead fans that frequent the Nightrider Performance Site, the original text and drawings are being presented. Changes used in the current Shovelhead engine build are also noted.

 With modification like this, it is quite possible for a Shovelhead engine to run with the EVO and Twin Cam engines.  We hope you find the information helpful.