Discussion in 'Subaru' started by littlejon, May 5, 2016.
We have a firewall forward package for the 750 that is proven. @azaleaaviation. It's worth a look.
rv6ejguy, I am just wondering if I stroke the EJ22 to get around 200hp instead of using a turbo, would that cause an issue? I would try and have it dyno'd, so that I know where the 130hp rpm speed is, so that I can set that as my high idle, but the extra horsepower might be able to take the place of a turbo? Any thoughts on that. Thank you.
Does anybody have numbers, like MTBF, preferably measured in comparable condition? Then, at least, you could argue with data.
It's much easier and much cheaper to get a new EJ255 or 257 short block as the basis for a larger displacement EJ than trying to stroke an EJ22. The 255/257 gives you some of the best current factory parts. If you go non-turbo, you'd want to change out the lower CR pistons for something a bit higher- maybe around 9.5 to 1. Lots of choices available from many different vendors. Forged is a good idea for aircraft applications if you're in there anyway.
You can then fit some SOHC heads which will save about 15 lbs. over the DOHC heads that normally come on the STi.
To get close to 200hp, you'd need cams and you'd have to rev it a bit higher too so pick your redrive ratio accordingly. Web Cams are used by many EJ aircraft folks with generally good success. Web Cam Inc. - Performance and Racing Camshafts The cams and cubes won't do what a turbo can do, especially at altitude, but they should get you to 180hp at SL or so and it will be at least 30 pounds lighter.
So I am thinking that if I build it to around 200hp, I will not run it at that horsepower, but it will give me a little extra power at my density altitude. I do not want to hot rod the engine either. I will rebuild the whole engine and plan to go with a different cam anyhow. I have read that the stock bottom end is very durable, so other then maybe stoking it, not a lot to change there. Thank you for the cam info.
You don't think 200hp might be a bit much on a 750?
Why not give the factory a ring? They're very open to alternative engines and might be able to tell you if this has been done before.
Have you compared any of the Subaru 6 cylinders?
What does the SOHC 2.7 weigh for example?
Yes, I think 200hp might be a bit much, but if I get it dyno'd then I would know what RPM 130hp is at and use that as my max RPM. My thought is that since I live at kinda a high density altitude, that if I have a little extra horsepower that it would help with the density altitude. Maybe that is wrong thinking? Also, if it is say 180hp, then my max RPM for 130hp will be lower which should help longevity of the engine.
I have not looked at the Subaru 6 cylinders, I have heard that they are like the EJ's with two extra cylinders. If that is the case, then they will weight too much for my application as the EJ22, from what I understand, will come in at close to 300 pounds and the max engine weight is 300 pounds. I realize that I will be giving up baggage weight, but I will be solo most of the time plus looking at 0-290's I will not be that much heavier with a modern power plant.
The old ER27 was only 145-150hp depending on the market version. Not many made, possibly a bit hard to find parts for, heavier and less power than an EJ25. I think with a gearbox, an atmo EJ22-26 is the only way to get 135-180hp and under 300 pounds total installed weight from a Subaru unless you turboed an EA81. Flygas Flygas Engineering makes some proper twin port heads for the EA81. Seems you could reliably make 150hp with these and a turbo and keep the weight down around 250 pounds perhaps.
I am glad to see the thread drift and personal attacks go away. This thread has returned to a discussion of Subie EJ's, which is what the OP asked about and Title implied.
If this is the case, then what is the advantage of this engine compared to some of the more "aircraft style" engine choices? Not wanting to start too much thread drift or rancor again, but since the Subaru auto conversion mentioned above (need turbo, need redrive, "around" 250 pounds "perhaps") is somewhat more complex to accomplish, what does it offer compared to the competition from the "aircraft" side of the fence?
The OP was interested in Subaru engines and wanted 120hp and to swing a relatively big prop at 5500 MSL. The DD Corvair will not meet that goal...
Again not trying to de-rail the thread, but to clarify myself I was not referring to a Corvair... I was referring to the 150HP Lycoming O-320 that is lightened up by using the new lightweight starter and alternator, and electronic ignition instead of mags. The CH 750 was in fact designed to allow this type of engine to be used, but they position the O-200 as the "standard recommended engine".
The O-290 Lycoming will be a little lighter yet (shorter throw crank I believe). The even lighter Lycoming O-235 (Cessna 152, PA-38) puts out 118HP in stock configuration, and with very minor modifications will put out 125-130HP with very high reliability.
My question regarding the Subaru is what specific advantages does it offer compared to one of these "genuine aircraft" style engines. My GUESS is that the Subaru can be more fuel efficient because of the EFI and more advanced controls. I'm waiting to know more about the other advantages that I cannot easily see.
Why not start a new thread rather than diluting this one which is under the Subaru heading?
The O-235 won't develop 120hp at 5500 feet. I don't see obtaining 130hp from one at 2700 rpm would be that easy or cheap.
I agree, the O-320 would be a good choice but I think the OP already considered this, which is why he asked about which Subaru engines might fit the mission.
Actually in most cases, the Subaru burns as much fuel as traditional aircraft engines, sometimes more in cruise. This has to do with generally higher frictional losses due to the higher rpm, which offsets most of the technical improvements such as better chamber designs, higher CRs and EFI/EI. Traditional aircraft engines fitted with EFI/EI are hard to beat for fuel specifics running LOP in cruise.
There are few categories in which the Subaru is notably better than the Lycoming, it's simply a different recipe which some folks prefer, like Chevy vs. Ford, Chinese vs. Italian food or Piper vs. Cessna. I have no regrets with mine.
Here are a few photos of other EJs in aircraft which I've been associated with. The first three are from my friend's Glastar which traditionally has an O-320 fitted.
His uses an EJ22 turbo, modified RAF belt drive and IVO prop. Gives him an impressive ROC and about 135 KTAS on about 8 GPH. This airplane has been flying for over 8 years and 250 hours. The engine has never been removed or opened up in that time.
The photo below is an EJ257 turbo driving an MT prop through an Eggenfellner Gen 3 gearbox. It's fitted to an RV7 which has trued 193 knots at 8500 feet. This puts out around 225hp at 40 inches and 4500 rpm. Fuel flow is around 8.5 gal/hr. at 170 KTAS. This has been flying for a few years, no issues to date. A similarly powered RV7 a few years back trued 210 knots (Vne) at 12,000 feet and 45 inches/5000 rpm.
As a sidenote, the EJs have been pretty popular in Glastars. Two of the high time Sube guys, Charlie Walker and Bill Yamokoski each had over 1000 trouble free hours on their EJ25s as of 2009. To quote Charlie " I use my GlaStar for cancer flts. and Medi-Vac flts. to the mainland and it has to be reliable. I love my E-Sube and sure wouldn't trade if for a Lyc. or Cont.............Charlie"
This is another typical EJ25 install in a Glastar. I believe this one has over 600 hours on it now.
Here's a vid of the RV7 turbo. Note the doppler shift in the overhead shots. No mistaking the speed of this thing. https://www.youtube.com/watch?v=No7BnIDAp-Q
Sidestepping the whole Subaru vs. Corvair thing...
Which Subaru engine(s) did you have in mind that will produce 120hp at 5500 MSL? At what engine RPM, reduction ratio, and MAP? What is the weight? The engines above in post 76 are great, but none seem appropriate for a CH-750; am I mistaken?
Either an atmo EJ25 or a turbo EA81. The EA81 turbo would come in around 230 lbs. EJ25 around 260 lbs. Either would produce 120+hp at 5500 feet at 5000 rpm. The EA81 running 35-38 inches, the EJ25 at 24-25 inches.
Ross--I'm not trying to be a smart@$$ with the following; I am hoping I can learn something from you. Please help me understand.
Regarding the EA-81, how does one get 164% of the engine's normally-aspirated power rating (see below) at 38 inches? Wouldn't 38" be more in the ballpark of 130% of normally aspirated power?
Maybe you're running a different cam and less restrictive intake & exhaust, but gosh, that sounds too good to be true. What am I missing?
Bearing in mind that the max. FWF weight for a CH-750 is 300 lb, your website says a 175 hp EJ-25 weighs 300 lb, not including starter, alternator, or exhaust. Is the 175 hp / 300+ lb version turbocharged (which perhaps would account for the 40 lb difference in the weights quoted)?
How does a 165 hp n.a. engine (highest rating I could find for the n.a. EJ-25 variants) produce 91% power at 5,500 MSL (that is, at 0.82 atm)? Or am I mistaken about the rated power of a normally-aspirated EJ-25?
Ross, is there a reason for not mentioning the reasonably common EA82T (turbo)?
And by EA81 Turbo I figure you mean to turbocharge one rather than the very rare actual EA81 Turbo?
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