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Four VW Powerplants

Different, yes, but they work!

By Tim Kern, EAA 825075, info@timkern.com

The air-cooled Volkswagen Beetle automotive engine lays out like a typical aero engine (four cylinders, opposed), but it was designed to power an automobile. Anyone who wants to power an airplane with a VW engine needs to make critical modifications.

Automobiles are rarely operated for long periods of time at high percentages of rated horsepower; an aircraft does it routinely. An auto engine’s peak horsepower is reached near the top of its rpm range; an aircraft engine turns a propeller, so (running in a direct-drive configuration) it needs to produce peak power at an rpm suited to the prop’s diameter, which is usually much lower than an auto engine. An automobile’s speed changes often; an aircraft typically cruises at a constant rpm. An auto engine’s power is transmitted through a clutch and flywheel or torque converter (reducing those nasty torsional vibrations); the airplane’s prop (in the typical VW) runs from the pulley end of the crankshaft, where neither the crank nor the engine case is designed to support aviation-induced forces.

Consider cooling, cowling, intake, and exhaust placement and design; ignition (and dual plugging if desired, but not always necessary in an auto conversion); accessorizing; and simply connecting everything together - and you have a lot more to do than what a first glance reveals.

From its humble beginnings, the Beetle’s horsepower (and displacement) steadily increased from 1100 cc and 24 horsepower to 1600 cc and 60 hp (at 4400 rpm). Although the higher end of the spectrum seems adequate for its power-to-weight ratio in many aircraft designs, modern professional conversions reliably make more - at a lower rpm (typically 3200-3400), but achieving those numbers isn’t trivial.

The quickest way to more power is through increased displacement. The base “Type I” 1600-cc Volkswagen uses an 85.5-mm bore and 69-mm stroke. Changing the bore to 92 mm yields 1835 cc (see table). This is popular because the stock stroke crankshaft can be used, though making the 92-mm cylinders fit the case requires light machining.

Displacement calculator for 4-cylinder VW engines

Revmaster only

bore (mm)











stroke (mm)











displacement (cc)











Bigger bores or longer strokes (popular crankshafts come in 78 mm, 82 mm, and longer strokes) require machining the case internally for clearance (“clearancing”) so that the connecting rods don’t come in contact with the case. (Popular crankshafts come in 78 mm, 82 mm, and longer strokes.) Small-block Chevy rods (with smaller-diameter bottom ends or even-smaller Honda rods) help, but they, too, require machining to make the bearings fit. As a practical limit for a do-it-yourselfer, even a gifted one, limiting stroke to 82 mm will make life easier; with a 92-mm cylinder bore, you net 2,180 cc. Strokes beyond 86 mm require custom cases with relocated camshafts.

Bigger isn’t necessarily better. “Oversquare" engines, (where the diameter of the bore is greater than the length of the crank stroke,) work well with high rpm applications; the opposite is generally true for peak torque at lower rpm. How much air the engine can ingest is intake-design limited, from the air cleaner (if installed) to the intake valve seat, including the combustion chamber design in some cases. The air/fuel mixture’s usefulness depends on how well it ignites and how tightly it’s packed (compression); these are largely governed by the ignition timing, intake shape, combustion chamber shape, and valve timing, which depends on camshaft and rocker geometry. Custom cam grinds (a “trailer” or “transporter” grind) will help. Increased compression ratio can add power. But as with any power increase, it also increases heat, can promote detonation, and can dramatically reduce time between overhauls.

The Big Four
Four American companies - Revmaster Aviation, Great Plains Aircraft Supply Company, Hummel Engines, which furnishes parts and complete engines, and AeroConversions, which sells AeroVee engine kits - represent different approaches. They also reflect different opinions about what works best.

Revmaster R-2200
Revmaster R-2200

Revmaster Aviation
Revmaster has converted VW engines for experimental aviation since the 1960s. Founded by Joe Horvath, Revmaster engines feature all-new parts, most of them proprietary to Revmaster. In complete engines, you see their production forged crankshafts (up to 90-mm stroke); Revmaster billet cams, valves, springs, seats, and keepers; Revmaster oil pump and filter mount; and accessory case.

RevFlow carburetor
The RevFlow carburetor can accept ram air. When paired with the optional alternate-air assembly and air filter kit, the pilot can switch between unfiltered ram air to filtered ambient cowl air.

The intake system begins with their proprietary RevFlow floatless guillotine slide throttle carburetor (throttle body injector) nested under the engine in a side-draft configuration. Typical installations are suited for gravity-feed, but use with a fuel pump is limited to 1.5 psi, which can be attained by way of a restricted return line. The mild-steel, mandrel-bent intake manifold tees off just behind the carburetor, and then splits into two pairs to feed each of the dual-port heads.

Revmaster heads
Revmaster heads are heavy-duty, thick-wall castings designed for large displacement engines with 40-mm intake valves and 35-mm exhaust valves, and machined for dual ignition application.

Custom-designed dual-plug heads with proprietary roller rockers, custom-forged connecting rods, and oversized external oil cooling round things out. “There’s pretty much no VW in our engine anymore,” said Joe. His shop is more machine shop than it is an engine assembly facility. Revmaster adds a full fourth main bearing at the pulley (propeller) end of the crankcase to support their robust prop hub, the largest in the industry. Revmaster also makes their own aluminum cases with a repositioned camshaft allowing displacements up to 3 liters.

The self-energized dual capacitor discharge ignition (CDI) package incorporates the dual-plug capacitor discharge ignition, a 30-ampere alternator, starter, flywheel, and accessory housing. No external electrical source (such as a battery) is required. Photo: Patrick Panzera

Ignition is handled by dual electronic ignitions fed by dual 20-ampere alternators. Joe said they cured a possible weakness in dual electronic ignition systems. “If you have an electrical failure, your ignition could shut down, so we designed our system with two, 20-ampere alternators and two separate regulators, so you’d have power whenever you needed it.” This system functions more like a magneto, not needing an outside power source to create spark. It’s all self-contained and fully redundant, and once running, it’s fully independent of the aircraft’s power system.

Revmaster R-2200
The Revmaster R-2200 counterweighted crankshaft is forged from E4340 alloy steel and is designed specifically for aircraft use only. Note that in addition to a tapered fit, the propeller flange is secured using a left-handed, threaded bolt that can’t back out from vibration.

All Revmasters have the ability to physically support and oil-control a constant-speed prop (through an SAE-1 flange, supporting props up to 22 pounds). A complete, ready-to-fly and test-run Revmaster R-2200, including stub exhaust, retails for $6,800. The R-2300, available spring 2010, will cost $7,100, and R-2500 and R-3000 engines with 90-mm strokes are on the way. In addition to complete engines, Revmaster offers a complete line of conversion and replacement parts, including automobile spark plug conversion assemblies for magneto harnesses, engine mounts (standard and custom) exhaust systems, magneto mount housing for those wishing to run mags, and a prop extension - not recommended for any other VW conversion.

1915-cc Great Plains VW conversion
Bill Stinson’s 1915-cc Great Plains VW conversion installed in his Thatcher CX4 as seen at EAA AirVenture Oshkosh 2008. Photo: Patrick Panzera

Great Plains Aircraft Supply Company
Steve Bennett, founder of Great Plains, started in 1977 with an engine straight from a junkyard. “In those days, you needed 75 hours to fly off your time,” Steve said. “That engine lasted 77 hours.” He learned fast, drawing from the expertise of Joe Horvath (Revmaster) and Rex Taylor (HAPI Engines). Soon, Steve started making prop hubs. Now, Steve sells parts, long blocks, complete engine kits, and complete test-run engines, and he offers direct drive from either end. He also offers Valley Engineering’s belt-driven propeller speed reduction drives, allowing higher crankshaft rpm and higher horsepower (traded for weight and heat, of course). Great Plains also has a complete rebuild service.

82-mm Great Plains-forged E4340 steel crankshaft
The 82-mm Great Plains-forged E4340 steel crankshaft is made in Germany and specifically designed for the rigors of driving a propeller. This crankshaft is shown sitting next to a traditional crankshaft. Prop hub retention is via a 3-degree taper fit and a 3-1/2-inch-long fine-thread bolt.

Steve’s parts business caters to those who want to build their own and avoid home-engineering and sourcing problems. Great Plains’ German-forged, American-ground crankshafts have an 82-mm stroke and even an 86-mm one, which use Chevy rods modified by Steve. His website is exhaustive as is his catalog.

VW Powerplants

His kits are modular in that you can mix and match long blocks with accessory packages, making for an almost endless combination of engines. Options abound, from which end of the engine you would like to hang your prop (with or without starter) to myriad ignition combinations. His parts catalog is a bountiful source of technical information—just a hint, however, of what’s available in his builder’s manual and DVDs.

flywheel drive engine
The flywheel drive engine has the prop hub attached to the “rear” of the engine, very near the #1 main bearing.

Advice for would-be pioneers: “Avoid getting your information from the ‘experts’ on the Internet. Some of them are very good, but as a novice, you can’t tell who the good ones are.”
For everybody: “Don’t rely only on rpm alone to tell you what your engine is doing. Add a manifold pressure gauge. You need to do your own tests, but you must know that, for instance, 23 inches will give you 75 percent power. Knowing your engine makes a huge difference in cooling and the engine’s life.” Typical values run “28-something at sea level up to about 2,000 feet MSL [mean sea level] for takeoff; cruise, 21 to 23 inches.”

Great Plains larger displacement engine cases
The larger displacement engine cases offered by Great Plains has reinforcement behind the #3 cylinder.

Great Plains produces complete engines up to 94mm x 82mm (2276 cc) and offers an assembly DVD and one of the best manuals available, useful whether you’re assembling a complete kit, using your own parts, or maintaining an engine you didn’t build. A typical 2,180- to 2,276-cc kit with dual ignition runs about $6,500, including true-redundant magneto and electronic ignition, starter, 22-ampere alternator, and exclusive Top Bug crankshaft and Force One prop hub and main bearing kit.

AeroVee 2.1 Kit engine
AeroVee 2.1 Kit Engine

Oshkosh, Wisconsin-based AeroConversions is a branded product line of Sonex Aircraft LLC, compiling the AeroVee engine kit since 2002 and offering the AeroCarb, a floatless guillotine slide throttle carburetor (throttle body injector). It provides the complete engine kit (the only way it comes), along with comprehensive building and installation instructions, including a video. The AeroVee is standardized: 2,180 cc (92mm x 82mm), and rated at 80 hp.

With only two moving parts (no float bowls or secondary jets to complicate things), a fine adjustment metering needle provides clean burning, smooth running, and fuel economy.

Sonex Aircraft’s Mark Schaible said, “[Customers] need to know that there is a lot of experience in the engines we sell. Everything is 100 percent new, an integrated collection of [over-the-counter] higher-end racing parts. We work with various vendors, assuring quality and that all parts will continue to be made for the foreseeable future.” Mark also noted the double-edged effect of having so much information on the Internet. “There is a lot of speculation and misinformation out there regarding bearings, prop hub extensions, etc.,” he warned.

All the pieces
All the pieces.

The AeroVee’s dual ignition is “all solid-state, with no moving parts, unless you count those “driven directly off the crankshaft/flywheel assembly,” Mark said. “We have two plugs per cylinder, but four spark sources, so even if three or four [plugs] stop working, you’ll still have ignition on two cylinders. That can get you safely down in most of the airplanes these engines are used in.”

20-ampere alternator
A 20-ampere alternator is standard equipment on all AeroVee 2.0 and newer engine kits.

Using aftermarket “racing VW” parts gives the Monnett family firm AeroConversions some flexibility. They don’t necessarily need to buy the most expensive parts available, saving customers money. “We redline our engines at 4,000, but normal operation isn’t over 3,500,” said Mark. “We don’t worry about ‘blueprinting’ the engine; it doesn’t run that fast…The case, for example, is a pretty standard aftermarket case. It already has the buttress at the back end; it’s clearanced for the stroke. All we need to do is check it and modify—for the special ignition, for instance.”

AeroVee 2.1
The AeroVee 2.1 features a purpose-built custom crankshaft that has a larger diameter and longer prop hub interface than previous versions. This new design also eliminates the distributor drive gear, eliminating the ability to drive an ignition from the distributor hole.

Still, there are custom parts: the shrink-fit prop hub, custom-ground camshaft, flywheel, billet accessory case, and intake elbows. The forged crank and Sky-Tec Flyweight starter are made specifically for AeroVee.

The AeroVee is the only VW engine approved for Monnett’s Sonex and Waiex, and it’s also popular in many other VW-powered airframes. The kit costs $6,495; magnesium cases are standard. The most popular big options are the assembled crank/prop hub assembly ($295) and aftermarket cast aluminum Nikasil-plated cylinders (a $500 option), offering a reported 9-pound savings over standard (iron) AeroVee cylinders.

Hummel 2180-cc engine
Hummel Engines & Machining 2180-cc engine installed in Scott Casler’s Thatcher CX4

Hummel Engines
Hummel Engines’ comprehensive line of VW-based engines (from 28 to 85 hp) grew out of demand for the late Morry Hummel’s 1/2 VW conversions originally made for the Hummel Bird. Master engine builder Scott Casler has developed and currently offers direct-drive, four-cylinder engines in 1,600-, 1,835-, 2,180-, and 2,387-cc versions, with ratings between 50 hp and 85 hp (at 3400 rpm). Hummel even makes optional extended-length Nikasil-plated aluminum billet cylinders in 92 mm and 94 mm, which save about 2.5 pounds each. The extended length means the builder doesn’t need to stack up shims to get reasonable compression, and he’ll sell them to any builder, not just his engine customers.

Hummel engine
A peek of the magneto can be seen at the rear of the engine, installed in Scott’s accessory case. Sharp eyes will also notice the electronic ignition elements and the Zenith carburetor.

A Slick magneto and a Hummel-special electronic ignition have separate drives for mechanical and electrical redundancy. A float-type Zenith carburetor is standard, but customers can request the RevFlow or the AeroCarb throttle body injectors. Standard VW tappet-adjusting screws are replaced by swivel-footed adjusters, and the sometimes-unreliable rocker shaft hairpin clips and springs by aluminum spacers.

Zenith carburetor
The Zenith carburetor is simple and inexpensive and features a cable-controlled choke, low-speed idle bleed screw, mid-to-high-range fully cockpit-adjustable mixture control, idle adjustment screw, replacement venturis, and float bowl vent.

Scott does all his own machining in-house, so if a customer has a request, he can usually accommodate. “I can make pretty much anything you need, including exhausts and engine mounts,” Scott said. He uses the Force One prop hub from Great Plains on the engines he produces. “It’s as good as they get. Why do anything different?” The Force One kit provides over four times the radial load-bearing area than the standard VW bearing. Hummel builds new engines, engine kits, and will supply parts for people building new engines as well as rebuilding them. In addition to selling just about any part to any builder, Scott’s price list includes machining customer’s parts, including cutting and welding heads and cases, balancing crankshaft assemblies, and installing sparkplug holes in customer-owned heads.

Force One kit from Great Plains
The Force One kit from Great Plains provides over four times the radial load bearing area than a standard VW bearing.

A test-run Hummel 2180-cc, dual-plug, stainless steel valve, American-head engine includes a 20-ampere stator-alternator, starter, dual ignition and stub exhausts for $5,850. Opting for Hummel’s light-weight, billet-aluminum, Nikasil-plated cylinders adds another $1,300.

There Are Differences
You’ll note that these experts don’t necessarily see eye-to-eye on everything: the need to relocate the thrust bearing near the prop hub and the need to reinforce the case near the hub (Revmaster); German-forged cranks and the ability to build for the prop at either end (Great Plains); in-house machining (Hummel); and the adequacy of the stock prop-end bearing and offering a kit-only product (AeroConversions). They also differ on oil recommendation, fuel recommendation, and on the need for, or efficiency of, certain assembly procedures as seen in their manuals.

Though prices are all very close for the 2,180-cc size engine (if you include the Nikasil cylinders on the Hummel), note that AeroConversions doesn’t sell builder parts, though spares are available as needed to previous customers. All these professionals offer extensive telephone support for their customers, and all these engines do the job very well.

Mounting systems differ. Electrical systems meet different needs, and weights can vary but not substantially. Before you buy, understand what you really must have and then look at what you want. You may get it ready-to-fly or in a kit, or you may wish to mix and match. You’re the experimenter - it’s up to you.

Tim Kern is a private pilot and certified aviation manager as well as an aviation writer and consultant based near Indianapolis, Indiana. You can find him online at www.TimKern.com.  

To read a companion article on Volkswagen engines written by Tim Kern, see the February issue of EAA Sport Aviation at www.SportAviationOnline.org/sportaviation/201002#pg94.

Revmaster Aviation
7146 Santa Fe Avenue East
Hesperia, CA 92345 (located across the runway from Hesperia Airport)
Phone: 760-244-3074
E-mail: revavia@aol.com

Great Plains Aircraft Supply Company Inc.
7011 N. 160th Avenue
Bennington, NE 68007
Phone: 402-493-6507
E-mail: info@greatplainsas.com

P.O. Box 2521
Oshkosh, WI 54903-2521
Phone: 920-231-8297
E-mail: sales@aeroconversions.com

Hummel Engines & Machining LLC
5464 East Storey Road
Coolidge, AZ 85228
Phone: 520-723-5283
E-mail: humeng@wildblue.net

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