I just found this on the interweb. Maxwell Propulsion System Billed s Subaru ej25 engines for airplane use. The load and 4.000+ RPM that a plain engine has to go threw for hours and hours on end.Here is just sum of what they have to say.
Background
Developed by Fuji Heavy Industries, the EJ series engine is the newest four-cylinder, four-stroke, internal combustion engine in the Subaru line. Most folks understand that you wouldn’t take a standard production car engine, install it in a race car, and expect to win the race. In fact, you may not even finish the race! Production automotive engines, with their standard oil and cooling systems, simply aren’t designed for continuous use at high speeds and high loads. The next time you’re in your car, check the engine rpm. I know in my cars - I have five Subarus - I usually cruise down the highway and through town at less than 3000 rpm. In contrast, a race car engine spends most of its life well above 4000 rpm, and many race car engines produce up to twice the horsepower of a production car.
Engine Oil Function
To increase engine reliability, the most important mechanical changes involve the bearing and piston-to-wall clearances. In order to understand the importance of a proper clearance, it’s essential to understand the many functions of engine oil. The engine oil’s primary function is to provide lubrication to reduce engine friction losses and wear. Since no lubricant is perfect, there’s still some friction and heat produced, and another very important function of engine oil is to help carry that heat away. In fact, oil carries off up to 40 percent of the heat generated by an engine. Corrosion control, cleaning, and sealing are also secondary functions of engine oil.
Bearing heat-load depends on several factors, the two largest heat producers being operating rpm and power density. In an automotive application, where it only requires 15 to 35 hp to cruise 60 mph with an rpm generally around 2400, the heat-load is significantly less than in an aircraft. Typically, in an aircraft setting, the Subaru EJ25 engine operates at upwards of 4000 rpm, producing 140 hp continuously for hours at a time. As a result, managing an engine’s heat-load requires more from oil and cooling systems than those found in most production automobiles.
Bearing Clearance and Tolerance
Loaded with excellent data, system operation descriptions, and inclusive troubleshooting sections, the Subaru service manuals are extremely complete and comprehensive. They also provide detailed information on the factory-defined tolerances and clearances. Interestingly, in an automotive application, larger tolerances are acceptable because the engines aren’t run very hard. On the other hand, bearing clearance is a critical issue in an aircraft application. For example, according to the Subaru Manual, the acceptable range for the connecting rod oil clearance is 0.0007-0.0018 inches. While a tolerance of 0.0011 inches might not seem significant, it actually allows an oil volume difference of 264 percent.
In other words, the larger clearance of 0.0018 inches allows 2.6 times more oil to pass through the bearing and thereby accomplish one of its primary functions: removing heat. This is a dramatic increase in terms of bearing heat-load management. At the lower end of the Subaru production engine clearance scale, 0.0007 is woefully inadequate for providing effective heat removal in an aircraft engine.
During the blueprinting process at MPS, all bearing clearances are set to allow a maximum of 30 percent difference in oil flow volume. Thus, not only do the bearings in the MPS engines get more flow, the flow is more balanced than the Subaru standard.
Flow Balance and Oil Pressure
A stable oil film (or cushion) is the layer of oil between the components of a bearing. In addition to keeping two surfaces from contacting each other and welding themselves together, this oil pressure wedge helps cushion vibration energy that would otherwise be directly translated into the stationary portion of the machine. An unstable oil film is unable to establish a continuous pressurized wedge of oil to separate the stationary and rotating surfaces. Instead, the oil wedge builds and collapses in an erratic manner. This fluid instability potentially results in a variety of mechanical problems.
The flow path of oil through an EJ series Subaru engine demonstrates that the #2 and #3 rod journals get their oil from the same pan on the crankshaft (#3 main journal) while the other rods have their own independent supply. To expand on the example above, if the #2 bearing clearance is 0.0018 and #3 is 0.0007, #2 gets 2.6 times more oil. In real-world conditions, oil pressure depends on demand - as demand increases with a steady supply, pressure decreases. In this example, the oil’s ability to lubricate is compromised. Not only does #3 receive less oil volume, but it also has a lower pressure oil wedge, since like any fluid, it will follow the path of least resistance.
Engine Blueprinting
Engine blueprinting is always an interesting topic for discussion. Let’s take a look at the motorsport industry standard for engine blueprinting. As described in Car Craft magazine’s article, World Guide to Blueprinting, the basic rule of thumb for setting rod bearing clearance is 0.001 inch for every inch of journal diameter +0.0005 inch. In other words, a 2-inch journal would have a clearance of 0.0025 inches.
The EJ25 engines have a journal diameter of 2.05 inches. By the motorsports industry standard, the Subaru-specified clearance of 0.0018 inches is a little on the tight side, and 0.0007 is well below the acceptable range. MPS’s experience with both aircraft and race engines has shown that 0.0016- to 0.0020-inch clearance is appropriate for producing a reliable and safe engine.
Subaru Myths and Facts
Over the past several years of working with both automobile engine clients and aircraft customers, I’ve had multiple conversations about a variety of Subaru issues. While there is always at least a grain of truth surrounding each concern, a more complete examination of the specifics reveals some interesting information. The three most common concerns and beliefs are described below.
1. Subaru’s factory-established bearing tolerances should never be modified.
This article describes the potential for bearing failures, but how many Subaru engines are affected? If you talk to any Subaru car dealership or repair shop, all will tell you that rod-bearing failures are the number one cause of Subaru engine failures. In fact, it has become so common that Subaru very recently changed the rod-bearing materials and modified the acceptable clearances. While we haven’t yet seen the actual details in print, in late November 2008 we disassembled a new EJ257 (2.5L WRX STi) short block and discovered that the bearings were made from a new, stronger bearing material. In addition, the tolerances on this engine were within the specifications that MPS has been using in their blueprinting procedures.
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http://www.eaa.org/experimenter/arti...ropulsions.aspI found this very interesting reading
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Posted: Sat Apr 23, 2011 12:19 pm 
