NSI Subaru EA81 Aircraft Engine Conversion

NSI Subaru EA81 100HP

ENGINE BEAT: June 1994

Like the story of the Stratus conversions listed elsewhere in this magazine, few recent developments hold as much prom­ise for the future of light-to-moderate weight sport aircraft as do the recent introduction of a series of Subaru engine conversions for sport aircraft use.

Light, powerful, highly reliable, and extremely well-designed in terms of aeronautical needs, the Subaru revolution may have as much of an effect on the mid-range of sport avia­tion as Rotax has had on the most afford­ able end.

Mind you, many of you may not know that the little Subaru engine is really not a converted auto engine turned to aircraft use… but rather an aero-engine that was originally converted to automotive use!

Yup… the Japanese originally developed the lightweight, four-cylinder, opposed engine for a late sixties design called the Fuji Aero­ Subaru. In the early seventies, it was re-developed for auto use in the FFI series and the rest is history; and, of course, it continues to make history… aeronautically speaking.

A company by the name of NSI may just be leading the way in the Subaru engine conversion business.

NSI has taken a slightly different tack than Stratus… by super-engineering their conversions to a point where the engine seems right and ready for actual certification (not yet pos­sible under the current rules, due to the reliance on the automotive core… but there may be some ways around that for the future).

Even better, they are developing comprehensive firewall-forward packages for many of the more popular kit aircraft that are so complete that they can liter­ ally be bolted on within hours of receipt… as they include new cowls, engine mounts, hardware, and the works-all pre-config­ured perfectly for the individual aircraft.

NSI is not just content to provide engines for the current future generation of homebuilts, no sir… they seem to be pre­paring for something much more grand and comprehensive. And it’s the initial effort that tells the true story of NSI.

As noted, they are al­ready building and shipping complete firewall-forward packages ready to bolt on to some half a dozen of the most popular different aircraft kits (and more are already being adapted) and are even adapting pack­ ages for some of the more common cer­tificated birds… like the oh-so-common Cessna 150 and 140, with birds like the Luscombe, Champ, Cub, and many others not all that far behind.

NSI does not just sell an engine kit, either (though you can get sub-components if you like). The engine package is shipped fully assembled, dyno-tested (including a copy of the actual print-out of the dyno run that each engine receives) and if bought as a firewall-forward package, everything one needs to bolt on the front of your bird and go flying… in as little as 10-12 hours!

The wunderkind behind this little gig is Lance Wheeler, a veteran of several heretofore-incomplete tries to build the ultimate sport aero-engine… and a run of efforts that finally seems to have paid off.

It is obvious that this guy is prepared to do this right. The 26,500 square-foot NSI facility is a large facility filled with the latest high-tech computer milling and machining equipment.

There are hundreds of thousands of dollars of the best machining gear available-precision gear associated with high-end avia­tion fabrication… and gear so high-tech that it has been used to support a number of NASA endeavors under separate contract with NSI.

Dozens of ready engine cores line the walls of the assembly area and hundreds of parts are ready to be built up, right now, into an engine and shipped off to a waiting builder. He, literally, has nearly one hundred engines’ worth of prepared parts ready to assemble… so he’s ready to ship right here and now. Yup… this guy is loaded for bear and he’s shooting live ammo.

Yes, he starts with a dependable Subaru EA-81 engine core… but only four major parts come from the automotive side of the game… the rest being fabricated on site or by a number of independent contractors.

The engine cores are bought, used, from Japan (and driven only by little old ladies on the way to the Ginza…), where they are stripped, disassembled, chemically washed, and inspected to make sure they meet basic specifications.

Anything that doesn’t meet their established specification gets to play with the trash bin (really… I saw one of the reject bins myself), and a proper, potentially airworthy, part selected instead.

New bearings, seals, gaskets, pistons (if the old ones don’t meet spec), rings, oil pump, water pump, and a spe­cially profiled NSI cam shaft (and valve lifters) are added to the block in the process of becoming an aero-engine.

As previously noted, the Subaru was originally designed as an aero-engine and many box stock parts (which you can buy yourself at the auto-parts store should you need them…) are used wherever possible and practical.

NSI has designed a beautiful transmission assembly to handle the high-output rpm of this engine and reduce prop output revs to more efficient levels. The 33-pound device has been deliberately designed to work with a linear cam device to reduce the slings and arrows of torsional vibration… a personal bugaboo of Lance Wheeler’s (this guy hates vibra­tion like some ex-Presidents hate broccoli).

EA81 engine panel

The reduction features a number of reassur­ing properties, the EA-81 reduction unit is capable of handling up to 240 hp and has a self-contained lubrication system that includes two magnetic particle inspection plugs. 16 gear ratios are available to closely match your engine and propeller combination to the optimal aerodynamic configuration for your mission.

There is an accessory pad capable of handling vacuum and fuel pumps. Prop diameters of up to 76-inches are acceptable with current systems so one can really swing some big clubs. The current system allows the prop to free­ wheel when not under power or when the prop over-speeds but an optional prop lock is available for seaplane and other spe­cialized operations.

The induction system is dominated by the highly-regarded Ellicin Throttle Body injection system… a device I’ve flown on a number of other aircraft with great satisfaction. The Ellicin TBI’s incredible throttle response (right now!!!) and simple construction for a dependable combo when matched properly with a powerplant… and it seems to really like the Subaru.

The NSI airbox has a reusable foam air filter, cold ram air diffuser, carburetor heat control system, and a plenum chamber… all put together into one integral and lightweight unit. It is one neat looking gadget, let me tell you. A firewall-mounted boost pump and gas fil­ter offer additional safety measures.

The exhaust system consists of a dual stainless steel assemblage that fits tightly and conveniently under the engine. Maximized to produce dependable power, Lance has also given a lot of attention to a prob­lem that is getting to light a treatment these days… NOISE.

NSI has done a great deal to quiet the savage charms of the Subaru and the result is one very quiet engine. Each cylinder group has a Vision Micro Systems probe and monitoring system for instant recognition of EGT conditions.

NSI has been pretty adaptable in terms of ignition systems. You can currently get a simple, inexpensive Subaru/Nippon Denso pointless, battery-powered distributor system similar to those used in the automotive powerplant.

NSI EA81 reduction drive

One has only to set the timing once and a simple tune-up is nothing more than the replacement of the plugs, cap and rotor, and adjustment of the valve lash to spec. NGK radio-emission-suppressive plugs are used. This is a simple and easy-to-use system-but if you run the battery down, you can kill the ignition system.

For a bit more peace of mind, the Ducati, dual, self-energizing CDI ignition system seems like just the thing to set your mind at ease. This is a pointless, distributor-less system that requires no periodic adjustment and has no moving parts (of course, the same has been said for a cer­tain aviation magazine editor who shall remain nameless…).

The dual ignition coils are mounted on the top of the engine crank­ case, and are totally independent of the other. This system is retrofittable to previously built NSI EA-81 engines. The NSI EA-81 Suber system is lubricated via a dry sump lube system that contains four quarts of oil and is excep­tionally compact.

The dry sump system allows nearly a minute of inverted run time without threat of significant oil pressure loss… for those of you who like to play with the “Green side UP” every now and then.

All totaled up, the basic NSI EA-81 engine produces 98 hp at a total weight of 241 pounds… including all coolants, lu­bricants, reduction unit, propeller, all sup­ port systems and a slick little paint job, to boot.

Charging capacity is 38 amps, and both automotive as well as aviation fuels are usable. Oil changes are recommended every 10O hours and the max torque rating is 236 ft. lbs. at 3800 rpm. Maximum fuel burn is 7.7 gph at 98 hp-but most cruise operations use a far more sedate 3.0 to 3.5 gph.

So, the proof of the engine is in the flying and the NSI was no exception. Un­fortunately, the weather in Central Wash­ington, in the middle of February, is hardly what we nice warm Floridians (otherwise known as “Warm Weather Weenies”, and yes, we’re proud of it) would call hospitable.

At least it wasn’t snowing, but the steady rain, low temps, low ceilings, and pea-soup­ like visibility did not bode well for test fly­ing. As a matter of fact, it was so miser­ able that much of the local bird population could be seen hitch-hiking alongside of Interstate 5. YUCK!

ea81 subaru aircraft engine

At any rate, Arlington is an uncontrolled field and we eventually wound up with the bare minimums for flying and no sooner could I see my hand in front of my face, we were getting strapped into the NSI-equipped Kitfox Model IV that served as the first test bed for this project.

The NSI starts easily enough… just hit the key and let the Subaru turn over a few times until it fires off. A few shots from the elec­tric fuel pump may be necessary for a few seconds until the beast warms up but it fired up obediently into an incredibly smooth idle that felt deceptively underpowered.

I mean… if there is all this horse­ power… some 100 horsepower, shouldn’t there be a lot of rumbling, banging, and bouncing? Well, that’s what you might think but the idle of the NSI engine is so smooth that outside of the noise and the gauge readouts, there is little to suggest the engine is actually running… no kidding.

After a minute or two of warm-up, temps came well into line for the upcom­ing flight and I worked my way out to the runway in the midst of a fair amount of rain and 12 to 18 mph worth of ever-growing wind. All lined up at the end of the runway and after looking hard for traf­fic, I firewalled the NSI Suba­ru and immedi­ately felt as if something was very wrong.

Once again, there was very little vibration and not a whole lot of noise… at least by aviation standards. Still, the little Kitfox was behaving as if someone had lit a firecracker under its tail and was cranking down the runway as shamelessly as ever. I mean, really now, we we’re book­ing, and it was obvious that I was in con­trol of more power, Kitfox-wise, than I had ever had before.

In no time at all, we were off the ground and rocketing upwards at 1500 feet per minute… but at a climb speed of 70 mph (hey, remember when Kitfoxes only CRUISED at 70?). I never did get to do a full power, max-rate climb because I never could get a stable climb attitude before I started losing myself in the low-hanging scud that enveloped Arlington for several days.

However, for a single pilot flight like mine, I would not be surprised to find that an NSI equipped Kitfox was capable of 2000 feet per minute. Cowabunga! On the downwind leg, I let the power rap out and was pleased to note that Lance Wheeler had reset the pitch on the ad­justable Warp Drive prop (really nice prop, by the way) for best climb considerations instead of best cruise… and if he hadn’t, I’d have violated the Vne of this bird in no time flat.

Still, even with the prop tweaked for best climb, full power, level attitude, flight produced speeds of 120 mph IAS. Z00000M —>

Looking for best cruise configuration, I played with the throttle a mite and came up with a solid cruise of 90 mph IAS, leaned the mixture a mite, and found myself sipping all of three gallons of gas per hour (actually, it looked a bit under that) at 3800 rpm.

NSI EA81 engine factory

Once again, the vibration level was deceptively low and one has to get used to the false sensation that there was inadequate power to fly on… simply because the engine was making no fuss at all (this thing is as smooth as some turbines… really).

Throughout the flight, temperatures seemed to be well within specification (if not a little on the cool side due to the ambient temperatures of the day) and the engine worked like a charm. Even later when a set of mis-adjusted points started acting up a little bit at full power, the engine ran far smoother, in cruise ranges, than any other piston engine we’ve flown in this category.

Yup… I was impressed.

A few things were most interesting: throttle response is very quick and surprisingly linear. Jam the throttle home and you are rewarded with nearly instant power. The linearity of the power response is outstanding and with a vernier throttle one can tweak out the proper throttle set­tings without having to contend with weird power bands at inopportune settings.

Ex­tended power runs with fixed throttle settings found the situation to stabilize quickly and produce little or no change over an ex­ tended period of time. Sev­eral minutes of flight at fixed power settings of­fered nothing more than slightly lower operating temps as the en­gine cooled a bit more properly and the rpm was effectively glued to where I left it. Very nice.

nsi ea81 dyno test

Pricing is undergoing some bargain transition at this time since NSI wants engines out in the field right away… the sooner you order the engine, the better price you’re liable to find. But suffice it to say that the equivalent Rotax 912 installation-with some 20 percent less hp-is several thousand dollars more expensive than anything NSI offers.

Is that a great deal or what???

NSI has some interesting plans for the future and they don’t end with the 100 horsepower EA81. A series of eight (!) en­gines is in the works that will offer every­ thing from the EA81’s 100 hp to the Subaru EJ2.2’s (Turbo Legacy) 200 hp!

Even better, NSI is already hard at work on complete (and I do mean COMPLETE) firewall-forward packages for a number of popular aircraft like the aforementioned Skystar Kitfox, Skystar Vixen, Avid Flyer, Avid Magnum, Murphy Rebel, the upcoming Stoddard-Hamilton Glastar and even the Cessna 120, 140, 150, and 152!

NSI kitfox

Yes, other engine combination are being studied… as Lance has asked me a number of questions about the Van’s RV series, various Lancairs… and he already has a great working rela­tionship with Stoddard- Hamilton.

Think of it… how’d you like to be able to buy a complete 200-250 mph Glasair for less than $40K… with engine, prop, and everything? Hmmm… I thought you would. Then again, so would I.

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2 Comments on "NSI Subaru EA81 Aircraft Engine Conversion"

  1. BTW this engine and airplane are still flying!
    550 hours so far. Just overhauled the cylinder heads.
    Builder of N45KC in 1992

    • Hi Kirby, thank you for your update! It is great to get this sort of feedback so people can understand just how good these engines are.

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