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Thread: Any Subaru conversions using the Subaru WRX turbo(250hp) engine?

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    Any Subaru conversions using the Subaru WRX turbo(250hp) engine?

    I've seen some kitplanes with Subaru engine conversions. The owners state, usually, around a 90 hp motor. How is this motor it terms of reliability and power? How long for over hauls, usually? Would it be possible to swap in a motor from a newer Subaru WRX? They are rated at around 250 hp with a turbo, bone stock, and the weight is about the same as a non turbo motor. Would this work? Could you use the fuel injection, also? What would the plane be like to fly, assuming it probably had a rotax 912 originally(100 hp)?

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    Super Moderator orion's Avatar
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    Re: Any Subaru conversions using the Subaru WRX turbo(250hp) engine?

    Subaru conversions have been at the forefront of alternative engine application. Locally, most of the packages I've seen are being used on Glastars, RVs and one or two Murphys, but producer web sites show a fairly wide variety of installations.

    So far the engines do have a good reliability history - the only problem I've seen anyone have is with the incorporation of the air sensors. The environment under the cowl of an aircraft is very different as compared to what you see under the hood of a car and so the installation must be able to account for those differences. As an example, one local builder, prior to his first flight, completed the engine installation and did all his initial tests with the cowl off. The engine performed as expected.

    With the cowl on the engine started and idled just as well. But as soon as the builder got onto the runway and started his acceleration run for his high speed taxi test, he discovered that the engine was developing only about 50% power. It took him several months of testing, tweaking and modifying before he discovered that it was the sensors that were at the root of the problem.

    For this reason most folks tend to recommend getting a firewall forward package from a reputable developer since they have already gone through this process.

    But while the engines are reliable, you have to be more careful with the selection of the reduction drive. It is this component that tends to be the weak link in the system and if improperly designed it could end your flight rather abruptly. This is again why you should do a bit of research and stick with a reputable manufacturer.

    Another thing to consider is that automotive engine ratings are not what you use in your airplane. Yes, the engine may be rated at 250 hp but in a car it is assumed that full throttle is used for only brief periods (seconds), if ever. For most of its life an auto engine develops on average only about twenty five to thirty five percent of its rating. In an airplane however, it needs to be able to deliver as much as 90% of its power for extended periods. For this reason that 250 hp engine would most likely have to be derated to something more appropriate, maybe in the 160 to 180 hp range. And then that has to be coupled to a proper reduction drive.

    But to answer your question, yes the engine can use the stock systems including the fuel injection. But be careful when you say something like "the weight is about the same". Being on the front of the airplane, even minor changes in weight can affect the balance of the aircraft. The additional weight of the turbo, additional manifolding, the waste gate, etc. is most likely not minor.

    As far as replacing a Rotax 912, not likely. The basic component weight of a 912 is about 128 pounds. Add in exhaust and cooling and the installed weight might be just under 150 pounds. I would guess that just the bare Subaru engine without accessories weighs more than that. Add in its own secondary systems and accessories and the installation weight would probably be well in excess of 200 pounds (and that still doesn't account for the reduction drive). Ignoring the balance, stability and control aspects of the aircraft for the moment, you'd most likely have to redesign the structural aspects of the whole front end of the fuselage. And then, if the installation increased the gross weight of the airplane, you would have to examine the rest of the structure also.
    Last edited by orion; July 18th, 2007 at 07:36 PM.
    "To live is to learn; to learn is to live" (author unknown)

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    Re: Any Subaru conversions using the Subaru WRX turbo(250hp) engine?

    Thank you. I didn't realize there was that much difference in weight. Also, the difference in horsepower ratings for auto vs. aircraft opened my eyes. Thanks again.

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