A premium ignition upgrade using 21st Century Technology!

PERFORMANCE: Any Performance Engine builder and Racer will tell you the advantage of having advanced timing in the Lower & Mid RPM range. They will also tell you Advanced Timing quickly turns into a disadvantage as RPM increases, as cylinder pressures and combustion chamber temperatures increase. Imagine the advantage your engine would have if the timing was automatically RETARDED as the RPM progressively increased!

Well, you no longer have to imagine!

DESIGN BACKGROUND: The Thunderbolt replacement has been in the works at HewTech Electronics for nearly 3 years. Early design attempts offered no Performance advantage over the stock units. Although we viewed the attempt as a technical failure, that wasn’t actually the case. The original Thunderbolt ignition was a very good CDI & represented the state-of-the-art system from the 1970’s. Even today, it’s better than most factory units. Our disappointment was due to no noticeable Performance gains over the stock CDI. We knew our effort was more reliable (better technology), but we wanted the same Performance gain that all other FIREPLUG CDI’s offered. We held off, while other CDI projects took precedence, but we never gave up thinking about the Thunderbolt replacement CDI.

August 2004; An idea occurred, which seemingly was ideal for the Liquid Kohler / Mercury Twister engines. The concept allowed increased timing control over the entire RPM range. This is a necessity for Hi-Performance / Hi-Revving engines; Advanced timing at Lower & Mid-RPM for performance, while Retarding timing at upper RPM’s for control of detonation and increased heat in the pipe for higher RPM’s. The stock THUNDERBOLT retards the timing approximately 4~5-degrees over the RPM range. Additional range would be a significant advantage!


Our concept proved to be everything we expected. We developed the FIREPLUG A.R.C. (ADVANCE RETARD CONTROL) knowing that a wider range of timing control would be an advantage over the original Thunderbolt CDI system. We discussed the “ideal” RPM/Retard range with engine-builders from both drag racing and oval racing. We determined the ideal system would retard the timing 1-degree for every 1000 RPM’s. For Example: If your engine runs from 3000 RPM’s to 11,000 RPM’s, you would see approximately 8-degrees of retard at 11,000 RPM’s. This is nearly 70% more timing range than the original Thunderbolt system.

Another advantage is NO BATTERY required! The FIREPLUG A.R.C. plugs directly into your harness, no additional power required. A 100% stock replacement with all the ADVANTAGES!


The advantage is PERFORMANCE! Racers and Engine-builders alike can now take advantage of increased initial timing (stronger hole shots, mid-range pull, throttle response) without the worries of detonation at the higher RPM’s, because the FIREPLUG A.R.C. retards your timing automatically!

The FIREPLUG A.R.C. is 100% compatible with ALL Thunderbolt CDI systems, and will operate in place of any existing Thunderbolt CDI, with the advantage of more energy and higher reliability. When replacing the Thunderbolt used on the Kiekhaefer Engines (Black-hood Mercs & Bolens), the timing profile will be similar to stock. The Advance Retard Control for timing requires other Liquid Twister ignition components to perform this function.



Advancing the timing will make the power band hit harder in the mid range but fall flat on top end. Advancing the timing gives the flame front in the combustion chamber, adequate time to travel across the chamber to form a great pressure rise. The rapid pressure rise contributes to a power band’s “Hit”. In some cases the pressure rise can be so great that it causes an audible pinging noise from the engine. As the engine rpm increases, the pressure in the cylinder becomes so great that pumping losses occur to the piston. That is why engines with too much spark advance or too high of a compression ratio, run flat at high rpm.

Retarding the timing will make the power band smoother in the mid-range and give more top end over rev. When the spark fires closer to TDC, the pressure rise in the cylinder isn’t as great. The emphasis is on gaining more degrees of retard at high rpm. This causes a shift of the heat from the cylinder to the pipe. This can prevent the piston from melting at high rpm, but the biggest benefit is how the heat affects the tuning in the pipe. When the temperature rises, the velocity of the waves in the pipe increases. At high rpm this can cause a closer synchronization between the returning compression wave and the piston speed. This effectively extends the rpm peak of the pipe. (See Eric Gorr’s website for all his 2-stroke performance insight)

ALL FIREPLUG CDI’s are manufactured using the best industrial-grade components available. The FIREPLUG is not a high-volume / mass-produced imported device. Every CDI unit is manufactured at HewTech Electronics LLC in Michigan, tested and shipped directly to you. It doesn’t exist until an order is received. Ask anybody currently running our FIREPLUG CDI ignition units.

There is not a better CDI available…period!

Additional information

Weight 1 lbs