2013 Engine Buyer’s Guide

Part 2: Alternative Engines.



While the world of engines for certified aircraft seems stagnant, the overall picture of alternative choices for Experimental/Amateur-Built aircraft looks positive, according to a recent sweep of the market. Nearly all of the engine manufacturers we listed in last year’s buyer’s guide are still hanging in there, and a few new ones have emerged. Some of the steadfast engine suppliers have even added to their offerings. So in this year’s engine buyer’s guide, we’ll look at what’s changed and what’s new since last year.

I try to keep in touch with the alternative-engine community throughout the year, seeking out new and different engine ideas, from one-off designs by ingenious homebuilders to full-production engine-development corporations. Last season, two new engines were added to this lineup, and we just learned that a promising company that was closed all of last year due to the unfortunate death of the owner has recently reopened.

As with last year’s guide, all of the major players (and a few of the minor ones) were contacted and asked what was new; the results of those inquiries are presented here. Companies are listed in alphabetical order for simplicity’s sake. If anyone has inadvertently been overlooked, please let us know by emailing [email protected] so that we can include you next year and add you to the online version of this resource. Now let’s get started.

Auto PSRU, formerly Geared Drives

Last year’s buyer’s guide announced the passing of Bud Warren, the power behind the Geared Drives Corvette engine and Subaru PSRU. After Warren’s death, the business assets were in limbo, but a sale was completed last December by Stuart Davis. He plans to pick up where Warren left off, continuing to support customers and fulfilling existing orders, an honorable business strategy. Warren’s designs were robust and refined, but they weren’t frozen. Notes and details concerning the next evolutionary advance were passed along to Davis, and he plans to incorporate them in his production of the drives.

Perhaps the most recent Geared Drives engine package to take to the air is Erik Franks’s, as installed in his freshly hatched Velocity XL-RG. (Photo: Erik Franks)


EPI’s Jack Kane offers high-performance engines for aircraft, automotive, marine and industrial applications. The propeller speed reduction unit (PSRU) pictured is his Mark-9 redrive. The prototype of this design reportedly accumulated over 800 hours of in-flight time in Lancair-IVP aircraft, including several races, countless full-power demonstration flights and extended instances of being flown in hard-IFR (by a brave pilot). In late 2000, EPI sold the manufacturing rights for the Mark-9 to the now-defunct EngineAir. However, EPI retained the design, drawings, engineering and manufacturing data for the Mark-9 gearbox. It’s a small, well-proven PSRU and is currently being put back into production with several improvements based on field experience. A custom version of a Mark-9 is installed on the GP-5 Osprey Sweet Dreams, one of the V-8-powered aircraft that competed in the 2012 Reno Air Races. The ECU-controlled, 625-horsepower V-8 engine, built by Paul Hasselgren, qualified at 363 mph, finished third in two of the heat races and finished fourth (359.6 mph) in the Sport-Gold race.

Reno Racer Sweet Dreams, designed and built by Andy Chiavetta, uses an EPI Mark-9 redrive. (Photo: Lee Behel)

Although the Mark-9 PSRU has been out of production for a while, data collected from its 15-year run on various high-performance aircraft helped bring its replacement, the Mark-15, online. Versatile in design, the Mark-15 can be machined to attach to several popular engines, including the ubiquitous small-block and big-block Chevy engines (LS-1, LS-2, LS-7), Ford Windsor engines and the Jaguar V-12. Custom interfaces can be designed and built by special request.

EPI is currently focused on the development of a high-power compression-ignition piston engine designed to operate on Jet-A and Jet-A1 fuel, but what’s really exciting is the announcement of its newest clean-sheet design, a 10.7-liter (653 cubic inch!), 60° V-12, which, in supercharged form, develops over 1200 hp. It comes integrated with the Mark-15 PSRU, geared accessory drive system and redundant coolant pumps and alternators. It weighs just over 700 pounds.


The General Motors Corvair engine has been powering homebuilt aircraft since 1960, with William Wynne leading the charge for the past 24 years. Every year he works on real evolutionary developments, as opposed to revolutionary ones.

The typical timeline of Wynne’s evolutionary development for the Corvair engine has been three years. He spends the majority of this time developing prototypes, testing them to ensure their proper integration with existing systems and various airframes, and reworking them as he sees fit. This is not a fast-paced and exciting process, but Wynne has never had a significant recall.

The 3100cc version of the Corvair engine is the powerplant of choice for the new Panther, shown here on display at AirVenture 2012.

“We don’t use builders as investors, and no customer is a test pilot,” Wynne said. “This may not be the industry standard approach, but it is mine.” This approach may not make one wealthy quickly, but it can earn you respect over time, and Wynne is certainly respected.

The most significant parts that made it through Wynne’s process in 2012 are new crankshafts made from U.S.-forged billets. Designed to complement the Corvair’s OEM forged-steel cranks, the new billet cranks have fillet radiuses that are twice as large as the original General Motors design. While they are not inexpensive, these cranks are a good value. A first-class, customer-assembled Corvair conversion built using one of these cranks still costs only half of what an imported turnkey engine of equal power would run. A Corvair engine built with quality components, specifically engineered for flight loads, is significantly stronger than engines from designers who placed weight reduction over reliability. Developments of Wynne’s product line include the testing of mechanical fuel injection, the introduction of the Flycorvair.net news feed and the availability of exchange short blocks with pre-installed fifth bearings used to handle the flight loads imposed on the crankshaft by the propeller.

The 2013 season will see further development of long-stroke variants of the new billet cranks that will produce displacements of 3400cc and 3550cc. With the stock Corvair engine’s displacement at 2700cc, the most popular displacements today are 2850 and 3000cc.

Four years ago, Wynne introduced fully developed overbore piston and cylinder kits and offered them to builders to convert their engines to these larger displacements. “These piston kits were the result of long and careful development, but generated little fanfare compared to the revolutionary new and exciting products of 2008,” Wynne said.

Raven Rotorcraft

Raven RotorCraft/ReDrives Inc. is now in its 17th year of producing reduction-drive kits and complete engine packages for the Geo/Suzuki, and now Honda automobile engines, for a wide range of homebuilt aircraft. The company’s professed goal (mission statement) has been to keep flying affordable through the adaptation of proven automotive technology and cutting-edge new product development.

Raven’s new Honda 1500XVT 140-hp, 210-pound turbo engine.

New for 2013 is its Super-STOL 140-hp turbocharged Honda Jazz/Fit 1.5L complete engine package. Everything about this firewall-forward package has been optimized for STOL operations and specifically tailored to the Zenith 750 and Just Aircraft’s Highlander kit aircraft. Variable valve timing and electronic fuel injection, combined with the company’s aftermarket turbocharging upgrade, give the best of both ends of the performance envelope: stunning takeoff power and economic performance.

Revmaster Aviation

Revmaster Aviation announced the beginning of its ASTM program, bringing the company’s 2330cc R-2300 into compliance with the requirements for use in Special Light Sport Aircraft (SLSA). This means Revmaster will soon have an engine package that can be specified by SLSA manufacturers for use in their factory-builts.

Revmaster’s 85-hp 2330cc R-2300.

This is a natural step for Revmaster because since its inception, the parts the company manufactured for its aircraft line of engines have intentionally followed the same manufacturing processes as FAA-certified aircraft engines. Revmaster did this with the forethought that in the event the company decided to go through the certification process, it would be ready. The ASTM compliance program, being less restrictive than FAA certification, is an in-between step for Revmaster and is exclusive to the company: It is the only VW-based aircraft-engine provider that makes virtually every part that goes into the product, giving them total control over the manufacturing process.

What this means for the SLSA manufacturers is that by the end of 2013, they may have an air-cooled, direct-drive, 85- to 90-hp, horizontally opposed, four-cylinder engine, priced thousands of dollars less than the current ASTM-approved engines that are available. And for experimenters, this means that the same exacting tolerances and quality control that go into ASTM compliance will be exercised in Revmaster’s engines, as they always have been.

Sadler Radial

While I was stoked to see the 65-hp Sadler Radial on display at AirVenture last summer, when I asked Donald Wehmeyer (company rep) for information to include in this article, he said the engine did not meet the company’s reliability standards and development was subsequently discontinued.

The 30-year-old Sadler Radial design appeared to be making a comeback, but now it seems that isn’t the case.

However, Wehmeyer went on to say that he has a radial design that uses the top end of the company’s 65-hp V-2 industrial engine (also converted for aviation), but it will have six cylinders and will be only 24 inches in diameter. The power output is projected at 195 ponies. It will have the EFI, ECU, SOHC, four valves per cylinder and use the same slipper rod crankshaft technology (marginally similar to what the WW-I Le Rhône rotary radial used), which does away with cylinder offset.

This radial engine isn’t listed in the accompanying table due to the fact that the crankcase hasn’t been built yet. A complete working version was built last year (dubbed R6-150), created completely from aluminum billet, but the end cost was just too high to put it into production. The company has since elected to use the proven head, cylinder and valve designs that are already in production to keep the cost under control.

Firewall Forward Aero Engines

The Camdrive 500 improvement project has been completed and Firewall Forward is now ready to offer a stronger and more versatile redrive solution for the Experimental market that requires a gearbox capable of up to 700 hp for a GM V-8. With this product, Firewall intends to pursue the restricted category of crop dusters worldwide. The Camdrive 500 is a helical-geared, idler-type PSRU, which allows the prop to rotate in the same direction as a certified engine. It also features two power takeoffs, one for a prop governor and the other for a vacuum pump.

Their belt-driven Honda conversion lineup remains the same, but with significant improvements to the Cam 125, making it more modern in terms of the electronics, which allows for tuning “on the fly” if necessary. They’ve added a turbocharger option for this engine, boosting it from 125 hp to 180 hp, with a dry weight of 294 pounds, including the radiator. 

Alternative engines. Click to enlarge table.


A review of even the last 10 years’ worth of the “what’s new” type of magazine features reveals that few revolutionary ideas survive the development cycle to go on and serve rank-and-file homebuilders. Almost all of the Experimental aviation success stories, from Van’s Aircraft on down, along with a majority of the engine providers listed in the table that appears here, are stories of careful development and a commitment to persistent pursuit of incremental improvement. While it might not be very exciting reading for those looking merely for entertainment, it is the proven path to providing builders with useful and lasting products.

If you’re interested in this segment of the aircraft-engine market, you should go to the shows and meet the parties making the products. Examine the engines for yourself, and take the information printed on the glossy brochures with a grain of salt.

If you’re looking for another way to see these engines in person, every year CONTACT! Magazine hosts an alternative engine fly-in. Most recently, it’s been held in collaboration with the Golden West Regional Fly-in and Airshow at Yuba County Airport (MYV) in California. This year the Alternative Engine Round-Up will be on Saturday, June 8. This is a great place to see many different homebuilt aircraft powered by all sorts of alternative engines, and it provides a chance not only to meet the pilots, but to listen to various vendors who host educational forums. The only cost is gate entry (unless you fly your aircraft to display with CONTACT!, and then it’s free), but you do have to pre-register.

The bottom line is that it’s your airplane, your dream and always your call. So choose wisely, because most homebuilding projects won’t survive a large financial mistake.

Patrick Panzera is the editor of CONTACT! Magazine, a nonprofit publication dedicated to Experimental aviation, with a focus on alternative engines. As mentioned, it hosts an annual Alternative Engine Round-Up. For more on the gathering, visit www.contactmagazine.com/roundup.html.


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