Sportster Detonation

Performance and Technical information on ignition for
Harley-Davidson Sportster motorcycles.

Solving Detonation on Sportster Engines

Detonation in Sportster engines is a very common complaint. From stock 883 through extensively modified 1200's, the Sportster engine is prone to detonation. Can the problem be eliminated or minimized?

The detonation problem with Sportster engines seems to stem from an improper advance curve. In Buzz Buzzelli's book on Sportster Performance, he describes the problem in detail. It seems that the Sportster engine runs best when full advance is reached at 3200 RPMs. The advance curve in various HD ignition modules gives full advance around 2500 RPMs. This leaves about 700 RPMs where the engine could be over advanced, leading to mild detonation. The recommended ignition settings and advance curve for Stock, Stage I and II engines (883 and 1200) is:

Initial advance 10-12 degrees
22-25 degrees advance at 2000 RPMs
28-30 degrees (full) advance at 3200 RPMs (recommend 28)

Not even the Screamin' Eagle ignition modules completely meet these requirements. The only ignitions that are able meet this criteria are some of the new programmable ignition systems like the V-Thunder. It must be noted that the programmable ignitions require a computer in order to modify the advance curve to meet Sportster requirements

Although the Screamin' Eagle ignition module does not exactly meet the advance requirements as recommended in Buzzelli's book, he does indicate that the SE Racing Module for Sportster and the early Sportster module (part number 32410-87) are acceptable in most engines.