The Viper series are the world's smallest commercially available spark plugs. The Z1 was originally engineered to meet the demand for high-tension miniaturization necessary to build smaller V8s, V10s, and V12s. As we build smaller and smaller engines the need for smaller spark plugs is unavoidable. Vipers were designed produce a hot spark and fit within the confines of our micro-creations- while maintaining scale effect.
The Z1 is the longest of the series with its insulator designed for the higher voltage systems and a deep reach for clean operation. The long insulator is perfect for multi- cylinder engines where the spark plugs must be significantly recessed into the head. It burns hot and is an excellent choice for both high performance and low performance engines.
Sometimes the same performance is required, but from a plug that would be a little more esthetically pleasing from the scale effect. The Z2 has a shorter insulator outside, but retains the same deep reach and internal features as the Z1. It will maintain the same operating characteristics as the Z1, but in many cases may look more realistic in smaller engines.
The Z3 utilizes the same insulator outside as the Z2, but has a shorter reach. It will perform as well as the Z1 and Z2, but accommodates those engines that do not need a deep reach or do not have the head thickness for longer threads. Although it appears to be a cooler plug don't let this one fool you. It has been used extensively in both high performance and low performance engines and it performs flawlessly for many, many hours at a time.
We discovered, in most cases, the shorter outer insulators in this series would operate at the same higher voltages without shorting to ground outside of the engine. Many of the Z3 plugs are operating on very high voltage CDI systems without shielding. This will vary depending on the proximity of the metal surrounding your plug however.