Subaru engines (1)
In my DR1050, I am planning to use an alternative engine: a Subaru auto engine conversion. On the Jodel mailing list, I have had some questions on these engines, and I figured that the answer might be worth a place on the jodel site too.
Mind you, this is only possible on homebuilt aircraft as no STC is available for these engines (interesting venture mightbe to get one though). And even then, not all countries might accept this on a homebuilt. So check first!!
My first engine was a commercially available product based on the (old) EA-81 Subaru 1.8 liter engine. The conversion was done by Stratus inc. from Seattle, a company that I (and many with me) can recommend wholeheartedly. These people are very knowledgable and honest.
The engine is a 85 Kg (dry weight, including all goodies like ignition and alternator, but no radiator, water or oil) alloy pushrod boxer engine that delivers something in the order of 110 hp (100 according to Stratus, but they are a bit too honest). The engine has a belt type reduction drive and can be made with dual ignition (factory option). It has two Bing altitude compensating carbs, the same as on the Rotax 912. Price for this engine used to be $6400 but may have gone up to $7000.
I bought mine second hand. Four of them had been fitted to an airship, before they decided that they needed slower turning props and therefore a different reduction ratio.
One problem with the engine is that it is too light. I would need about 30 to 35 cm between firewall and engine to keep the CG in place. And with the prop offset due to the belt drive it would simply look odd on my DR1050. At first I thought I could live with that. Later I decided that I wanted to keep everything underneath a stock cowling. So I sold it. The engine is now on the nose of the Rans S6S of a friend of mine. Performance and reliability of the the engine are excellent.
The next step up in the Subaru range is the 2,2 liter EJ-22 as found on older Legacy models (I believe they are called "Liberty" in some countries). Don't bother with the 2 liter EJ-20 as they are either SOHC 115 hp models at the same weight as the EJ-22 or much heavier DOHC models. The latter aren't available in Europe but might be down under. The EJ-20 is not available in the US. I have also skipped the EA-82, the successor of the EA-81 as it is too heavy for the power it delivers, and it suffers from some valvetrain problems. Many rotorcrafts do use this engine though.
The EJ-22 in stock form will deliver 135 hp. There are numerous vendors who sell engines based on this block, and all have reground their camshafts, as the original ones have the torque peak too low in the RPM range. Properly recammed (SOHC), the EJ-22 will deliver an honest 160 hp, although up to 200 has been claimed by some (prepare your pinch of salt here).
The EJ-22 is rather rare here in Holland. On my quest for an engine (I want to do the conversion myself, with the help of that friend of mine with the Rans), I came across a nearly new EJ-25 (2.5 liter, you have guessed it). The 1998 model is DOHC and slightly wider and 8 kg heavier than the EJ-22. Total width is now equal to that of my Potez (or an O-200). Total weight will be about 135 kg. That's 30 kg heavier than the Potez, but with the CG of the engine itself closer to the firewall than with the Potez, the CG of the aircraft will hardly shift. It will effectively turn my Jodel into a two seater though, as we will not exceed MTOW, desipite the 65 extra HP, right?? :-)
The torque curve of the EJ-25 is much more favourable to aircraft use than that of the EJ-22. Peaking at 4400 RPM, this would give me an excellent cruising RPM. Max power is 165 hp @ 6200 RPM. I will redline the engine at lower RPM to have a max hp rating of 150 in aircraft use. That should be plenty for the Jodel!! :-)
Having run only 8000 km, the engine will not need to be overhauled, just inspected. The cams will not need to be reprofiled.
Features that I am planning:
Vendors to choose or to avoid:
An excellent source for Subaru knowledge is the airsoob (for Air Subaru) mailing list:
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