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There are a lot of unique challenges that present themselves when engineering the best performance ignition components for circle track racing. Any form of racing, from dirt to pavement, beats the tar out of every component bolted to that race car, so an ignition system must be built to handle the constant abuse. Second, these engines stay at higher RPMs for a long time! Unlike drag racing, where max RPMs last for just a few seconds, once the green flag drops, the ignition system will be at the far end of the tachometer, pushing redline rpm until the race is over.
Lastly, and probably the most troublesome for ignition engineers, is the number of different rpm limit rules imposed throughout the country. In order to maintain a balanced race field and to keep race budgets at a fair level, many racing sanctioning bodies institute rpm limits in different classes. This has always been a challenge for each sanctioning body, as well as any ignition company, but MSD has always tried to work with the sanctioning bodies and racers to develop ignitions that deliver reliable performance for the racer as well as the rpm limits and ‘tamper-resistant’ ignitions for the racing sanctions. To learn more about several of MSD’s most popular circle track ignitions, we spoke with Holley’s Graham Fordyce about the different ignitions available and the technology that the rules committees embrace.
“MSD offers several ignitions designed specifically for circle track racing,” Fordyce said. “First there’s the HEI Distributor (p/n 8362CT) for classes that mandate a stock HEI. If an ignition box is accepted, the MSD 6CT is the best choice, for classes with an RPM rule. In many classes such with IMCA, RUSH, WISSOTA, USMTS, USRA and more, these products are mandated.”
The MSD 6CT (p/n 6427) and 6CT Pro (p/n 6428) can provide full output spark with a 6-volt supply voltage. The 6CT Pro can add a momentary switch to reset the high-RPM recall. Both ignition systems have a digital RPM readout that can be adjusted with the rotary dials to within 100 RPM. This adjustment is accurate to within a tolerance of one percent, so racers don't have to worry about going over their RPM limit.
For classes that mandate a stock appearing HEI distributor, the PN 8362CT may look like any other cast aluminum HEI distributor, but this one has been hot rodded from the inside out. “The shaft is the same one used in our billet line of distributors so it’s a strong, precision-made shaft that is treated to a friction reducing QPQ coating,” Fordyce said. On top of the shaft is MSD’s proven mechanical advance assembly with TIG welded weight pins, chromoly weights and different springs and stop bushings to setup the timing advance for each engine.
As for the spark output, a lot of research and development went into the ignition module and coil. The challenge for any HEI distributor is to create a high output spark at higher rpm, and by matching the right module with an efficient coil, this distributor gets the job done – and then some.
The MSD Circle Track HEI distributor (p/n 8362CT) is a stock-appearing HEI distributor that is built with the demands of racing in mind. Don't let it's looks fool you...the Circle Track HEI is built to take the punishment.
When a CD ignition box is allowed, the 6CT is the mandated box in many classes within the higher ranks of circle track racing. “The 6CT is designed to deliver high voltage. We’re talking up to 150milljoules of spark energy with the p/n 8250 coil,” Fordyce explained. “The box is made to be tamper-proof with exclusive fasteners on the back panel, plus the circuits are encapsulated so it cannot be taken apart.”
Another unique feature of the 6CT that was designed with input from racers and from sanctioning bodies is the digital readout on top of the box. For classes with mandated rpm limits, the tech inspector can verify the highest rpm reading that the ignition reached simply by turning the ignition off and back on. If the class limit is 7,000 rpm and the box flashes 7,200 rpm, they’re caught! “The only way to reset the high rpm recall is to have the ignition on for 20 minutes,” Fordyce said.
To keep the rpm value within class specs, the rev limiter of the ignition can easily be adjusted with two of the three rotary dials below the LED read-out. The limit is adjustable down to 100 rpm increments and is accurate to within +/-1% so racers can rely on not going over their mandated rpm thanks to a very smooth rpm limiting action that won’t upset the chassis or engine.
MSD's Digital Soft-Touch HEI Rev Limiter (p/n 8727CT) plugs into any HEI Distributor and features an RPM limiter that can be set via rotary dials, from 3,000 RPM to 9,900 RPM in 100 RPM limits.
There are other features built-into the ignition that are useful to the racers as well. The LED display can be used as a tachometer. This is helpful if the box is visible while tuning the engine, when necessary to check RPM while adjusting the carburetor or setting timing. “There is a 10 or 20 degree start retard to help engines with locked out timing get fired up. Also, you can switch the rpm readout to show battery voltage. This is a handy feature for racers that don’t run alternators,” Fordyce explained. “Check the voltage before a feature, then right after to see how much the battery went down.” You will notice over time that the voltage drop is fairly consistent, and if the drop in voltage is significant it’s probably time to change the battery.
As for supply voltage, the MSD 6CT and 6CT Pro are the only ignitions that will produce full output sparks with a supply voltage of only 6-volts. At that low a voltage, the car won’t restart, but the ignition will continue to produce full output sparks. It’s also important to note that there are two versions of the 6CT: the standard version (p/n 6427) and a 6CT Pro (p/n 6428) as Fordyce pointed out. “The only difference is that with the Pro version you can add a momentary switch to reset the high rpm recall. These ignitions are primarily used in late model classes or any classes that do not have a mandated rpm limit.”
(The 8727CT came before the 6CT, so it was the acceptance of the 8727CT that lend to the development of the 6CT.)
Specialized fasteners on the back of the ignition box and encapsulated circuits make sure that the 6CT ignition boxes are tamper-proof. Good luck with trying to sneak one by the inspectors!
Neither of the 6CT Ignitions would be present if it hadn't been for the wide acceptance by many sanctioning bodies of MSD's Digital Soft-Touch HEI Rev Limiter (p/n 8727CT). This compact device plugs into any HEI Distributor and features an rpm limit that can be set via rotary dials from 3,000 – 9,900 rpm in 100 rpm increments. Just as the 6CT, the LED will display the highest rpm reached during the previous race to make race officials happy. Also, if there’s ever an interruption in the connection to the distributor, a fault code will be displayed!
The 6CT Ignition, HEI Distributor and Digital Soft-Touch HEI Rev Limiter show MSD’s commitment to circle track racing, sportsman and hobbyist. “These ignition products have all been developed through input from tech officials and race teams alike,” Fordyce added. “We give racers the performance and reliability they crave and the details to help the tech officials. We’re just excited to be a part of so much great racing!”
Another thing to consider is that with the encapsulation of the internal components of the 6CT series ignitions: they are virtually waterproof! Don't believe us? Here's proof that they will work completely submerged under water, so have no fear when it comes to pressure-washing your race car. Sharp eyes will notice that this particular machine was owned by Steve Francis, who is now the Tech Director for the Lucas Oil Dirt Late Model Series!