Success with Subaru STI

[Randy]

Hadley,

I hope to convince you to go with turbocharging as it is already proven to work well. Think of the possible problems that can come along with engineering a new approach. It can and probalby would add considerable cost and many more hours of engineering and installation of a new system, then improving it, and chances are it may never really work out.

Congratulations on getting the airframe completed! If you go with a turbo installation from the beginning I think you will be very happy with the power and ease of control of boost, tuning etc.

The heat issue is just something to be very aware of and take precautions. It is not difficult to protect the nearby exposed items from the heat. It just needs to be done. I probably over did it but the heat is not going to burn anything in my cowling. Your higher OATs will not make that much difference in my opinion.

I am willing to share all I know about my turbo installation. I can email you lot's of pictures etc. showing everything I had to do. I did have to work out several bugs in the installation and it got very frustrating. You can take advantage of my learning curve and get it right the first time. You can even take advantage of the little changes I have been making to the SDS tuning. There is lot's of help and information available for a turbo installation. I think you will be pretty much on your own with a different aqpproach, and that can get lonley indeed, especially when you start flying behind something that you mihgt not be so sure of.

One of the most important things you can do for safety is to get rid of the throttle by wire setup that is part of the Subaru ECU. A pilot should have control of the throttle, not some darned computer!

I say put a turbo in it and take advantage of the available information on a system that works well! After all the upgrade stuff you have had to do already, why go off on another experiment?

Convinced?

Randy C

[Randy]

"i thought the guy who blew up his STI due to wastegate failure failed at 52". you and Ross say the engine is designed to run at 57". for your cruise what is max sustained pressure that won't destroy it? jan told me max was 45". you have operated well in excess of that number with no apparent harm."

Hadley,

That happened to a single cam H4 that was supposed to be turbo normalized only. The wastegate, (actually a dump valve) failed on him and it over boosted an engine that was not designed to be boosted. The STI is built for boost. It needs boost to make good power. As long as you take reasonable precautions to prevent detonation, the STI engine can take one heck of a bunch of boost and will simply pin you back in your seat rather than self destruct. When I first started flying mine with the supercharger I routinley saw 52" on take off. I have since come to my senses and feel that is excessive and not needed.

It is very interesting and educational to search out some Japenese car hot rod shops in your area and see what they do with these engines. I have seen every day commuter Subarus putting out 500 HP to the rear wheels on the dynomometer, with stock internals on the engine, just bolt on stuff and tuning. That is the beauty of this engine in the airplane. Even at full power I am only using a portion of what is available in the car in stock configuration.

For other readers out there, I fully understand that the airplane world of constant relatively high power usage is much different than what the car sees. That is the reason I like this engine. 75% of it's rated horsepower is 225. At full power I probably am getting somewhat more than that, but the reliability factor of only using part of what it is capable of (in the car) feels very very good to me

I do not know what maximum sustained pressure the engine can take. Depending on altitude, it will cruise around 200MPH at around 42" MAP and 4400 RPMs. I can tell you that it can take that power setting for several hours at a time with no issues what so ever. The engine is not straining very hard at that setting. If you boost it much more than that you will find yourself needing a different airframe that is built for higher speeds.

The great unknown is how long will the package last compared to the standard engine configurations and we just don't get to know that until we get there. At least replacement costs will be less when the time comes.

Randy C

[Hadley]

Randy, Ross and Rotary,

you all make great points and thanks for the new data. you all have valuable experience and i would like to explore the turbo option more before moving forward. Randy, i would also like to take you up on your installation photo offer. i know photos would remove some of the mystery. i would also like to discuss some stuff by phone if possible. Ross, i will follow up with a pm and i am working on skype to be able to call you afford ably.

i have to run to the airport right now to meet my local engineers, hopefully they have read these posts. i will send more later.

again my thanks;,

Had
512-342-0022 Hm/Off
512-203-6861 Cell

[ajay]

Originally Posted by rv6ejguy

Yes, I agree. This package would have great potential in a Rocket-like modified RV to take advantage of the higher TAS offered at altitude or something like a Lancair. The engine is probably too light to fit a Rocket without extensive mods.

Ross,

Not too educated on the subie, but as I was reading this thread, it got me thinking,

If this produces power comparable to the IO 540, what about the turbo STI for the RV10? How light is this setup?

Curious what your pros and cons are for this vs your EG33 setup? What's the ball park HP you are expecting from your turbo setup?

ajay

[rv6ejguy]

The STI is really too light for an RV10 without extensive lengthening of the nose and moving the battery forward. Could be done of course and you have an impressive useful load. Performance would be pretty similar to a 260hp Lycoming. It's a thought but a lot of work.

The EG33TT will be 15-25 lbs. heavier than the 540 but give 275hp for takeoff and much better altitude performance just like the STI does over the 360 Lycoming. Big con of all this stuff is the sheer time and work to do the mods. Big pro is if you can do it, it is a lot cheaper than the Lycoming- that is if everything goes smoothly and works well the first time.

For most people, the Lycoming is the way to go in a -10. It is just a very hard check to write out.

[fmarino1976]

What is the estimated HP the STI is putting out? Ross, you mention that it would be too light for the -10, but what about HP? Just curious...

[Randy]

Cinsider that the STI is rated at 300 HP @ 6,000 RPM as installed in the cars. That is at a higher level of boost and higher RPMs than you will likely use in the plane, but I guess you could with the right gear ratio in the PSRU. My setup is geared approx. 2 to1, so @ 2700 Prop RPMs I see a maximum 5400 Engine RPMs.

One of the bigger challenges in using this engine has been to learn how hard to push it in the aircraft environment. I like the reliability factor of only using a portion of it's rated power, even at what I would call full power in the airplane. Using all 300HP in a larger airframe might work, but you had better like experimentation with a capitol E.

Randy C

[Unkgd]

All,
I have an 04 STI and it is a wonderful car both on the street and on the recetrack (track days only - haven't done "wheel to wheel racing"). One of the things the 2.5 liter STI engine is sensitive about as a car engine, is detonation. I blew my first engine (#4 con rod bearing) on the track at 1100 miles due to this issue. This was on a track in the desert and the ambients were in the 100+ degree F range. I believe the intercooler got heat soaked and the inlet air temperature was too high for the ECU programing. After a few other "infant mortality" failures, Subaru reprogrammed the ECU to be slightly less agressive on the ignition timing.
BTW - I had the same issue on an overboosted 1st gen MR2 - and it was due to the same heat soak issue.

On the stock internals, you can probably safely make about 350 - 375 hp with high octane gas (about 100 or so) with about 20 psig boost in street use.

If I installed one of these in my plane (and am considering the possibility) it would have redundant knock sensors to prevent the detonation issue from occurring. There are reliable systems out there to do this - such as J&S UltraSafeguard and MSD.
A properly sized intercooler would also be essential for safe operation - especially when taking off after siting idleing on the tarmac on hot day.

The only other caveat I would offer is I am not sure what the fuel effeciency of this engine would be. On the track I average about 4 - 6 gpm - and you can figure I am at full throttle maybe 30% of the time. On the street it will run between 16 - 24 gpm depending on whether it is city or highway - and is somewhat speed dependent. So at a guess - I would put it in the same range as 350 chevy small block.
My 2 cents (if that)
Bill

[rv6ejguy]

It is highly doubtful that detonation can cause a rod bearing failure before the piston rings lands succumb on a turbo engine. Never seen this failure mode in 30 years of building and racing turbo engines. The factory knock sensor system overrides any pre-mapped ignition timing values and pretty much quashes any detonation possibility.

Rod bearing failures are typically the result of insufficient bearing clearances on high revving engines and Subarus are somewhat unfortunately known for this in factory trim with wide variations in clearances.

High IATs past where the system is mapped to would typically cause a richer mixture as charge density is reduced. Fuel is generally trimmed with increasing IAT. In some cases, fuel is added past a certain critical IAT to reduce pre-ignition possibilities. A good intercooler system is important for best power and reliability with the lowest possible boost pressure.

As far as power output, the STI would have no trouble matching the typical performance and hp outputs of a 260hp Lycoming 540 IMO, including making 195hp in cruise.

[Unkgd]

Ross,
You are correct about the broken rings lands on the stock hypereutectic pistons . I forgot to mention that occurred as well, as the obvious and memorable indicators at the time was the knocking noise under load and the loss of power.
Broken ring lands and rod bearing failures are still an issue for those people that are "tuning" their stock engines - even the later 07+ STI models. The Nasioc website has quite a bit of info on the issue - though you do have to sift through some of the information
Regards,
Bill