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EFI infiltrates Rock Racing

Words: Brandon Flannery; Photos: Brandon Flannery and Image Off-Road Photography

One sport just waking up to the benefits of EFI is Rock Racing. The rigors of rock racing have long created fuel delivery problems. However, there’s new fuel ignition technology on the market that is changing the game for competitors throughout the highly-demanding sport.

Carburetors work well on flat ground, and have for a century. However, their floats and bowls don’t like being violently bounced, shaken, or put at odd angles – let alone upside-down. For many buggy owners, the solution has been a switch to propane. When correctly plumbed, the pressurized liquid gas gets into the engine, regardless of angle.

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The Oxygen sensor can get false readings and increase fuel if the EFI isn’t set up for open headers. Placing it upstream in a primary tube is suggested, though the system’s settings will be based off of that particular cylinder’s performance.

While that solves the delivery issues, it comes with its own set of problems. Propane has a lower Fuel Energy Constant (FEC) than gasoline and requires more air to burn. Given an engine’s set operating volume of air, and needing more of that space to burn less fuel, well it’s easy to see why propane is not exactly a “performance fuel.” Another complication plaguing many buggy owners is the propane system freezing up below 40 degrees, making cold-weather riding a bit of a challenge.

When Clyde Bynum received another engine for his “play” buggy, Venom, it came with a self-tuning FAST EZ-EFI system. Unfortunately, once installed, the EFI ran erratically and, unfamiliar with tuning, Clyde was a little discouraged.

“It was supposed to ‘learn and tune’ itself,” he says. “But, while it did run good wide open, it would load up and run real rich at idle and part throttle. It fouled plugs quickly and was sluggish off the line. I began questioning my decision and put it on propane. It ran decent on the LP, but it would freeze up when the temperatures dropped.”

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The switch to EFI in rock hoppers can be done on an existing four-barrel intake. No more floats, bowls, or erratic running under extreme conditions.

Clyde is a part-owner in Spyder Off-Road in Memphis and runs the Southern Rock Racing Series, a rock-hopping series quickly gaining in popularity. (Guys from Iceland have come down to bounce through the South’s gullies.)

He’s also friends with Nick Kortenber, who owns “Warfare,” driven by Danny Sullivan, and handles the maintenance on “Screaming Blue,” a wildly popular buggy driven by Bobby Tanner (do yourself a favor and look up Screaming Blue on YouTube; prepare to be amazed). That buggy was recently converted to FAST EFI, and went on to run the King of the Hammers competition in California, with a significant increase in performance.

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Kevin Winstead of FAST set an initial tune based on known engine data, such as displacement, compression, and fuel type.

Nick assured Clyde the FAST system was the way to go, and that he just needed to make a few changes. One of them was to upgrade from the EZ-EFI to the FAST XFI Street system. After closer inspection, they found the Oxygen sensor was causing the overly rich condition. EZ-EFI is designed to work with a full exhaust system, and the buggy’s open headers allowed enough reversion to occur that oxygen was pulling back up to the sensor, fooling it into compensating for a lean condition. XFI Street is a little more forgiving with open headers, and the O2 sensor was moved deeper upstream in one of the primary tubes. Now, with an accurate reading and the proper tuning in the XFI, the rich condition was resolved.

Concerns when tuning a buggy like Venom include more focus on throttle acceleration enrichment. Since rock racing is basically drag racing uphill, drivers need instant and accurate throttle response, often in stabbing bursts rather than long periods of wide open throttle like a regular race car.

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Once started, adjustments were made to dial in the off-idle, part-, and wide-open throttle to make sure the rapid response demands of rock racing are met.

Fuel pressure is another concern, and Venom’s needed to be slightly increased to compensate for the required flow Clyde’s ethanol needs. With the injectors running at the upper levels of their duty cycles at wide open throttle, there is always room for more, but Venom is not a competition buggy; it’s a weekend stress reliever for Clyde’s family and friends.

Another aspect of the FAST XFI is the option to run different fuels if the parameters are known. Clyde picked up Excite Fuels as a sponsor, and they suggested he try their 114 Red, a 90-percent ethanol/gasoline blended race fuel that has shown 10 percent power gains in dyno testing. Its Fuel Energy Constant (FEC) is around .68, and the suggested “safe base” Stoichiometric Air/Fuel ratio for the 11.5:1-compression 355 was started around 8.5, with the advice to pull a little timing out. FAST EFI tuner Kevin Winstead came in to help set the tune.

The Stoichiometric A/F mixture is the ideal rate a gasoline engine burns all fuel with no excess air. For example, gasoline’s mixture is about 14.7:1. This means that for every one gram of fuel, 14.7 grams of air are required. The A/F ratio for the Excite 114 Ethanol falls in the 9.5:1 range, requiring 9.5 grams of air per gram of fuel. This means you can pack more fuel per volume of engine air for combustion, increasing power. It also has a lower burn rate that creates a cooler engine charge. The engine’s warm-up time was even a little slower under the new fuel.

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Wide-open pulls were made to dial in the right air/flow ratio and check the performance of the injector duty cycles. This one was running right at the top of their capacity on the Red 114 Ignite ethanol blend.

The FAST XFI allows variables to be entered for FEC of common fuel and adjusts the ratios to suit. Ethanol-enhanced fuels are quickly gaining popularity by burning cooler and making more power at lower prices than similar-octane gasoline. If racers wanted to switch back over to propane (or keep their system intact and better manage it), FAST XFI has settings to do just that.

Another benefit of the FAST system is the rev-limiting that cuts both the fuel and spark at the same time. This is much easier on the engine and valvetrain, and offers smoother transitions back to operating RPM, without the additional fuel left in the cylinders of an ignition-cut limiter.

As more racers overcome their fear of “fuel infection” and learn more about the tuning, EFI should grow to be a popular choice in rock racing. With buggies like Warfare and Screaming Blue leading the way with success, other racers are sure to follow. For more information, you can always check out the FAST website or call their tech line: 1-877-334-8355.

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“Warfare” is owned by Clyde’s friend, Nick Kortenber, and driven by Danny Sullivan. It’s always a crowd favorite.

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Bobby Tanner in Nick’s “Screamin Blue” has been setting the buggy world on fire and recently switched to FAST EFI. Bobby is a wildman behind the wheel and does very well when he heads out west to run the King of Hammers competition in California.

Sources: FAST,; Spyder Off-Road and Performance,

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