Conversion - T2 Revmaster

Rev - Nov 11, 2017

 By Jan Zumwalt (EAA #66327)


See Also

Revmaster R-2300 Specifications

HP Rating: 85 @ 3200
Continuous HP: 80 @ 3000
Fuel min octane: Aviation grade 91/98 – 100LL
Conforming to ASTM D910
Oil: multi-grade 20/50
Bore: 94mm Stroke: 84mm 4 main bearings
Displacement: 2331 cc
Firing order: 1 – 4 – 3 – 2
Compression ratio: 8:1
Spark plugs: 12 X 3/4 reach DCPR7E
Carburetion: RevFlow 36mm
Ignition: Quad CDI 8 coils
Timing: BTDC 25 degrees
Dual alternator: 20 amp each
Battery: 12V min. 20 amp
Crank flange: SAE #1 4-3/8″ bolt circle
Dry weight: 170 lbs.
Cruise rpm: 3000 +/- 200
Idle rpm: 900 +/- 50
Oil temp min: 130 degrees F
Oil temp max: 220 degrees F (measured at sump)
Oil pressure min: 10 lbs/1000 rpm
Oil pressure max: 80 psi
CHT cruise: 350 – 375 degrees F
CHT climb: 450 degrees F
EGT full rich: 1250 degrees F
EGT max; 1400 degrees F

For those builders that are contemplating using the Revmaster 2300cc engine: There has been some confusion over the parts used in the build by Revmaster. Some time ago Revmaster had solved the problem of the center main bearing problem that had existed when the engine was boosted to the larger size 2100cc + sizes (same as other engine builders). There had been a problem with the crank pounding the #2 main bearing to oblivion.

I contacted Joe at Revmaster and inquired about this problem and this is the comment that I received: The #2 center main is not a standard VW dimension. It has been increased to 60mm which increases the bearing area of the crankshaft, reducing excessive wear due to the increased size and HP of the engine. (NOTE: This is a standard VW Type 4 60mm main bearing size (the Type 1 is 55mm main bearing). The production version of the R-2300 is magnesium but will build a Aluminum case (like the Type 4), if the customer wishes. The aluminum case is 18lbs heavier than magnesium. (NOTE: This is equivalent to the Type 4 (18 lbs) engine weight)

By Patrick Panzera, EAA 555743,
Introduction by Tim Kern, EAA 852075,


Revmaster Aviation has finished development of its latest upgraded engine and the results are in: more horsepower at any usable rpm. The new Revmaster R-2300 (2331-cc) engine maintains Revmaster’s renowned proprietary systems and parts including its RM-049 heads that feature large fins and hemispherical combustion chambers. It maintains the earlier R-2200 engine’s maximum 82 hp at only 2950 rpm continuous, but offers 85 ponies for takeoff at 3350.

The additional power ultimately comes from a 94-millimeter bore plus lengthening the stroke to 84 millimeters, but that’s oversimplifying things. “We’ve put a lot of energy into this redesign,” says Joe Horvath, president and founder of Revmaster Aviation. “On paper it looks like just a few minor modifications, but we’re really closer to a complete rework of the internals: crank specification, connecting rods, pistons, and cylinders are all new.” The longer stroke results in greater displacement, longer connecting rods yield better vibration and power characteristics, the lower cruise rpm allows the use of longer propellers, and the higher peak horsepower can be felt in shorter takeoffs and steeper climbs.

Strength and reliability are boosted by Revmaster’s four-main-bearing, 4340 forged steel crankshaft (boasting nitrided journals) that runs on huge (as compared to a stock VW) 60-millimeter center main bearings. Thrust is handled by the custom-installed 55-millimeter #3 bearing at the prop end of the crank, formerly found at the other end. Fully utilizing its robust, proprietary #4 main bearing, the Revmaster crank has built-in oil-controlled variable-pitch propeller capability, a feature unique in this horsepower range and exclusive to Revmaster VW conversions. Unlike other VW conversions, props other than wood are usable on any Revmaster engine of any vintage.

RevFlow mounted under a Corvair engine attached to engine test stand.

Revmaster has been in the engine business since 1959, starting out as a remanufacturer of the early 36-hp engine that was introduced in the Volkswagen Beetle. In 1960 the VW was upgraded to the 40-hp engine that has become the cornerstone of VW flight engines. Around that same time, Revmaster developed a 2000-cc version of the VW for the experimental aircraft market by first manufacturing target drone engines for Northrop Corporation. Revmaster spent about two years in this endeavor before discovering thrifty and resourceful homebuilders were using some of these drone engines in experimentals. With many of the installations being highly successful, Revmaster decided to go in that direction. Now with well over 40 years experience in the homebuilder market and literally thousands of engines sold, Revmaster is announcing the latest addition to its successful lineup, the R-2300.

Although the Revmaster is based on the VW engine, not much of the original engine remains. From a proprietary crankshaft to proprietary heads, including a modern electronic ignition with individual coils for each of the eight sparkplugs, this isn’t the old shake-and-bake VW conversion of yesterday. It’s more a purpose-built aircraft engine than it is an automobile engine conversion no matter how it’s measured.

The Crankshaft

Connecting the propeller is always the most difficult part of adapting an automobile engine to aviation use. Not that it’s particularly difficult to physically accomplish, but rather that the loads imposed on the crank by the propeller are considerably different than those in an automobile. Potentially, the worst of these loads are gyroscopic in nature, although some might argue that torsional loads, especially harmonics that can be amplified by the propeller, are much worse if not a close second. Throughout the years, ever-increasing displacements have multiplied the strength of the power pulses and have amplified the propeller effects. And through trial and error, it’s generally accepted throughout the VW engine community that the propeller used on a Volkswagen conversion should be wood and be as light as possible. This isn’t the case with the Revmaster, and carbon fiber, aluminum, and even variable-pitch propellers are open for consideration.

Throughout the decades that experimenters have been flying behind the VW engine, there have been a number of different ways used to attach the propeller hub to the crankshaft, most of which have been to simply bolt a custom hub to the pulley end of the otherwise stock crankshaft using the same method that the generator fan belt pulley is retained. It wasn’t until Revmaster clean-slated the crankshaft design to include a precision taper fit of the hub to the crank that the VW conversion crankshaft was made robust enough to handle props other than wood. This fourth bearing rivals that of any certified horizontally opposed aircraft engine.

Where the stock VW crank steps down twice to smaller diameters and has two keyways,
one for the distributor drive gear and the other for the fan belt pulley, the Revmaster crank has
been beefed up and then precision-ground for the 3-degree taper.

Other VW engine conversion companies have tried to emulate the design (a short list would include HAPI, Great Plains, and now AeroVee), but none has come close to the total package Revmaster has developed. This package includes, among other things, a left-hand threaded retention bolt that tightens with vibrations (not one that’s prone to loosen) and the elimination of the stress-riser inducing keyways that others still use.

Just behind the steel cam drive gear is the #3 main bearing. Where this would be
a normal plain bearing in a stock VW, Revmaster has machined the case to
accept one of its custom thrust bearings manufactured in house.

The total package is rounded out with the installation of the previously mentioned fourth main bearing that has substantially more surface area than the original three combined. It replaces the oil slinger, the ignition timing gear, and the comparatively insignificant automotive front bearing that’s designed to carry only the fan belt loads. The case is line-bored to accept the new fourth bearing as well as the larger-than-stock Revmaster main bearings, and the adjacent engine case web is machined to accept the otherwise stock VW thrust bearing that normally resides at the opposite end.

The new, one-piece, bearing-grade aluminum alloy (designated B850) tubular fourth bearing is machined from a casting and is slid over the crank prior to the hub being fitted in place and the cases closed up. The bearing is held in place by essentially an interference fit between it and the case halves, locking it into place. The prop hub bolt is installed but not tightened until after the case halves are bolted together and torqued to specification.

The prop hub itself is machined from a single piece of 4130 or 4310 (steel) forging that is then heat treated for hardness to ensure the locking effect of the precision-honed 3-degree taper. The previously mentioned left-handed retention bolt is ¾-inch in diameter and is torqued to 160 pounds/foot, locking the taper so securely that any form of externally applied puller will destroy the hub before it can be removed. However, through the use of carefully placed internal threads and the properly sized “drive bolt,” the hub can be removed and replaced numerous times with no damage to the hub, crank, or bolt.

Deep inside the steel propeller hub is a set of threads into which the “drive bolt” is installed. When
driven in far enough, the bolt bottoms out on the nose of the crank, forcing the hub off with symmetrical
loads and safely removing the hub with no damage to any of the parts involved.

When I visited Revmaster during the build of the engine for this article, the technician slid the hub into place and secured it by patting lightly with the palm of his hand. He then asked me to pull it back off, which I couldn’t do. He had to use the drive bolt to pull it back off as a demonstration of the strength of the taper fit.

The Crankcase

The crankcase starts life as a stock off-the-shelf Brazilian-made magnesium VW part. Although Revmaster can obtain aluminum cases, magnesium cases are far lighter and have thinner cross sections in various places. Once received at the Revmaster facility in Hesperia, California, the crankcase undergoes extensive machining to allow its integration with Revmaster’s other components.

Due to the relative distance between the centerlines of the crank and the cam, it’s easy to see that the engine can only be “stroked” so far. This is one reason that Revmaster opted to make their own case for the larger R-3000 engine we wrote about in CONTACT! issue 82. That same case can be used for the “tweener” 2500-cc engine, but Revmaster feels comfortable tweaking the stock case to the 2300-cc engine featured in this article. Since the global market is so unreliable, the future availability of the Brazilian magnesium cases is always in question, and that’s one of the many reasons Revmaster developed its own case. For now, however, it’s more economical to buy the off-the-shelf case and modify it, but with its own case, Revmaster isn’t locked in to a sole source should it ever dry up.

Bore and Stroke

As previously mentioned, the stroke is ultimately limited by the cam location, but Revmaster has found a way around that. Stroke is usually defined as the distance traveled by the piston from zero degrees to 180 degrees of crank rotation. Another way to look at it is the distance between the crank pin centerlines as measured when 180 degrees apart, so moving the pin’s centerline farther away from the crankshaft centerline increases the stroke. When the stock diameter pin is moved away from the crank centerline, as it rotates toward the cam, the clearance between the rod and the case is decreased.

What Revmaster does is to not move the stock diameter pin farther away from the crank centerline, but rather to grind the stock pin smaller in diameter, removing material from the surface of the pin that’s closest to the crank centerline and resulting in the pin’s centerline being moved outward as shown in the illustration above.
There are other clearance issues such as interference between the connecting rod cap or bolts and the crankcase or even the opposing piston skirt. These are addressed with traditional, proven methods, but the use of proprietary connecting rods with streamlined bolt lugs goes a long way toward solving these issues.

There are other issues that arise when stroking the engine, the most obvious being taking care of the compression ratio, but in this instance, there’s one issue that’s not so obvious. When the piston is at the bottom of the stroke, care needs to be taken to provide enough support for the piston skirt. Revmaster handles this with the custom manufacturing of cylinders with longer spigots that enter farther into the case than stock cylinders.

On the left is the special Revmaster cylinder designed to support the piston all the way
to bottom dead center of the bored and stroked R-2300. Contrasting on the right
is a stock VW cylinder. What’s not shown is the additional machining to the spigot
end of the cylinder that’s necessary for clearance.

The deeper spigots do create other interferences inside the case that have to be dealt with, but Revmaster has refined solutions for all of them.

Connecting Rods

Forged 4340 steel I-beam connecting rods have 100 percent machined surfaces and utilize 9-millimeter ARP 2000 rod cap bolts. They’re balance-matched into weight groups of +/-3 grams. The “big end” carries pressure-lubed plain bearings from a General Motors application, rotating on 2-inch polished and radiused journals. The small end (with bronze bushing) connects to full-floating VW wrist pins that are retained by spiral circlips. Splash-style lubrication is used effectively to get oil into the wrist pins and piston lands via strategically placed orifices in the piston interior and the rod end.

Note the substantial differences between the crank end of the stock VW
connecting rod in the foreground and those attached to the crankshaft.

Although a lot of parts that go into the Revmaster conversion are proprietary, the company tries to use off-the-shelf parts wherever they can. The pistons are high-performance forged Mahle parts. Note how short the piston is and that when it’s at BDC (before dead center) the rings are inside the case.


The camshaft is a chilled cast-iron unit with a lobe hardness of 60 HRC . In the casting process a “chill” (a metal piece placed in the sand mold) is used. These “chills” act as quenches which remove or “wick” heat rapidly from a specific area in the mold. The rapid cooling makes the metal near the chill much harder than the surrounding material without the chill. The hardening depth goes significantly beyond any other hardening process.

The custom grind of the R-2300 isn’t particularly noteworthy (270 degrees duration with a 0.39-inch lift), being on par with a lift and duration for low rpm/high torque as one might suspect. It performs well between 2500 and 3400 rpm, with peak torque at 3200. Revmaster services the entire spectrum of automobile applications for the VW engine and will grind one of their camshafts for just about any profile for any application. The stock (aluminum) VW cam gear runs against the otherwise stock VW crank gear at the front of the engine, while the cam itself turns in pressure-fed plain VW bearings.

The areas around the combustion chambers have been beefed
up to easily accommodate 92- to 94-millimeter bores.

Rough casting as it arrives at Revmaster Aviation.

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