Success with Subaru STI

Randy Crothers in WA has been test flying his 7A recently, equipped with an MT prop, Gen 3 gearbox, custom turbo in place of the supercharger and an aftermarket ECU replacing the OEM ECU.

He's showing 170 knots true at 7500 MSL at 42 squared (4200 rpm and 42 inches MAP). At 10,500 MSL he's showing 175 knots true at the same power setting. Total fuel burn was 13.77 gallons for the 1.4 hour flight for an average of 9.83 GPH including the climb and descent. Turbine inlet temp was 1620F.

Aircraft does not have gear intersection fairings in place at this time.

Not too shabby so far. Some more tweaks to come with aerodynamic and cooling system cleanups should give a few more knots.

Kudos to Randy, a talented guy who does all his own work and tuning and did not give up on the STI dream.

Nice

A great performance numbers!

Frank

I'll see if we can get a link to the takeoff video I've seen. Takeoff and climb is quite impressive and it sounds great.

Coolant temps acceptable range? How hot was the OAT?

All temps are pretty cool but I suspect OAT was as well. It's winter in Washington State right now. Cooling mods are coming soon as it is highly doubtful that cooling would be adequate in the summer months with the current setup.

Many of the STI guys are fitting custom radiators now. There is good sharing of info on one of the Sube dedicated forums now so we hope the process of getting all the bugs out will progress somewhat faster than it has for the last couple years.

Randy was the first to take the big step of turbo and new ECU and get it flying. Several others are following suit.

that's great ross. keep us posted as he gets hours, always good to hear how it is working from someone with the engine running on his plane.

Wow - those are some good performance numbers indeed. I'll be really interested to see the cooling mods and how that all comes out with summer temps.

It's almost enough to make me reconsider a Lyclone IO360 for my bird. Good thing I've got about a year to watch from the sidelines before it's time to write a check....

Hi all,

Mt STI package is working much better after changing to the turbo charger and the SDS system. Part of this involved getting rid of the throttle by wire setup and that in itself made a big difference. The Subaru ECU was making too many adjustments for airplane use. Logged data showed the timing moving all over the place. With the SDS system I have a mixture knob and full control of the programming of the timing etc. and the timing is stable, not jumping around like it was.

The end result is the engine has a bit less power, but more margin to detonation and that is a trade off I can easily live with and over time I will be able to get that power back.

No sense reporting on temperatures in the winter, no problems at all but no test either. I am in the process of ordering larger ratiators and a new oil cooler. Not looking forward to that fiberglass work but I know the changes are needed for summer time temperatures.

It is kind of fun to tell someone you were running at 45 square at 10,000' and watch them absorb what I said...

In my mind it is a bit early to claim success. My goal has been to achieve lycoming performance with this smooth modern engine. That will take more time to prove out but I am very happy with the way it is working for me at the present time.

Randy C

I forgot to mention that I sent that little video clip to Ross as I don't know how to link to it here. We will just have to bug Ross to make it available.
Randy C

Video Link

Here is the link to the takeoff video on YouTube: http://www.youtube.com/watch?v=om1GUJ5m1nY&feature=channel_page

Turn up the sound and enjoy.

Gotta like that climb angle in the last 4-5 seconds.

For sound comparisons here is a takeoff on my EJ22 turbo 6A at 38 inches and 4800 rpm: http://www.youtube.com/watch?v=kjNsbU6nFAw&feature=channel_page

Congratulations Randy and watch that detonation. It will beat the devil out of your pistons and your turbo.

The compression ratio on the STI is 8.2 to 1 and Randy is running on 100LL at the moment. There is no danger of detonation on this combination at the manifold pressures he is running. On mogas, he'll possibly have to alter the ignition timing a bit to be safe. He's running 32 degrees right now I think.

This engine comes from the factory turbocharged running about 55-58 inches on 92 octane fuel and has all the goodies like under piston oil jets and very thick piston crowns, pins and ring lands, forged rods, forged crank and sodium filled exhaust valves on some STIs. They are much stronger than most factory naturally aspirated engines. Remember the 960hp drag motor with the stock case and crank!

Randy, I think these engines are fitted stock with a 6 heat range NGK plug. I run 7s in mine and they are none too cold. You might want to consider getting some 7s in there before switching to mogas.

Sounds and looks great! Dare I ask how much $$$ went into this setup? I'm thinkin about this for the -4... although the electric CS prop is still a little bit of a hangup...

I went to colder range spark plugs a long time ago when I first started using the engine and saw how white they were.

I hate to take any of the timing out in order to run mogas safely, but I have learned to listen to Ross I suspect that is why he is running a Mogas 100 LL mix in his plane. I may have to go that route myself.

As for cost of this engine package: Someone like Ross could probalby put something like this together and come out saving considerable cost over buying a Lycoming. Buying a firewall forward product, and then making all the changes that have been needed, has made this a very expensive engine package.

Randy C

My CR is 9.45 to 1 so I'm being super careful with timing and MAP on mogas. I've reduced TO power to 35 inches now from 38 and just re-wrote all the checklists and flight manual to reflect new power settings. You should be much better off with your lower CR on mogas than I am.

Glad to hear you already have cold plugs in there.

STI Testing Results

I performed some more cruise power testing today with my turbocharged STI powered RV7A.

I climbed up to 15,500' using 4400 RPMs and 40" MAP all the way to test sltitude, and I kept exactly the same power settings for a four way speed measurement, then I immediatley descended and fueled the plane to check the fuel burn. I am not fully confident in my fuel flow readings yet but testing this way should be pretty accurate, no? The fuel actually consumed does agree with my fuel flow meter so maybe I have it dialed in OK afterwall.

I took the results and ran them through the little program on Randy Lervolds site, plugging in the GPS ground speeds from 4 headings of 0, 270, 180 and 90degrees.

The average came out at 184 knots, or 211 MPH. I was up for a total hobbs time of 1.3 hours cruising at each heading long enough to finally get it stabilized and get photos of the EFIS screen etc. Getting it settled down at that altitude was not easy. It took 10.35 Gallons to top it off, for an average fuel burn of 8.5 GPH. 8.5 GPH @ 15,500 for 211 MPH cruise. I am happy with those numbers!

I then went back up to 8000' and did a North and South run at exactly the same power setting of 4400 RPms and 40" so the fuel burn should be the same. This gave me an average of 162 knots or 186 MPH on 8.5 GPH, (assumed). I do not yet know for sure where 75% power is on this engine, or whether it really matters I know I can easily add more boost and or RPMs and hit Van's published performance numbers, especially at the top end...

On the way home, while up at 8000' I moved the power settings up to 4750 RPMs and 47" MAP. I accidently blew right through the VNE of 200 knots TAS and I still had more RPMs and boost in reserve. Fuel flow indicated 71 lbs / hour, or 11.8 GPH. I am none to proud of accidently performing a flutter test, but I am amazed at the capabilities of this engine prop combo.

FYI it is an RV7A with 2003 Subaru STI engine and MT MTV7 electric constant speed prop. MT weight is about 1250 lbs. so it is not a light weight setup, but the performance is there. I am running the Simple Digital Systems engine control unit after finally giving up on making the stock Subaru ECU work properly. Ross Farnham helped me with sizing the turbo charger correctly. I will still need to improve cooling for summer temps. Airframe is fairly clean but no intersection fairings on the main gear legs.

Randy C

Holly Cow!

Outstanding Randy, you've got a wicked fast and economical RV package there.

I hope this puts to rest some of the theories bandied about here regarding liquid cooled auto engines not being able to match air cooled aircraft engines on speed and economy. You've vindicated those "slow" MT propellers here too. They seem to work on Subarus anyway. Frankly, your success even exceeded my expectations.

I hope you will make that trip to Van's sometime to get the final, unbiased word on the subject. Some of our Lycoming friends are still not going to buy it.

It sure is nice when all those hours of hard work and frustration pay off like this.

I was going to warn you again about Vne this morning. Well now, the flutter envelope has been cleared- in level flight.

Engine life is the last thing to prove. You are slamming the hours on there pretty quickly. No more 47 inches stuff, ok?

Thanks for the report.

<<Well now, the flutter envelope has been cleared in level flight.>>

Note to all, Ross was kidding here. That's not how to conduct a flutter test.

Randy, congratulations! Proceed carefully, ok?

Good show! I knew the STI engine had more potential than anyone had produced before. I hope that you can get the coolant stuff worked out without loosing too much of the top end.

Who Has the Fastest 7A?

The silence here is deafening.

Anybody else here have a 4 cylinder 7A which can true over 200 knots in level flight? Not that we should be doing that of course. Hint- we are looking for pix of your EFIS for bragging rights.

But wait theres more!

I did some more fuel flow testing today with what I think is a more accurate method as follows. I get stabilized at altitude, speed, and power settings, then switch to a full tank and carefully time the flight under those conditions, and then measure the amount of fuel required to fill that tank.

At 169 knots TAS @ 4500'. 3800 RPMs and 38" MAP measured exactly 8.9 GPH. I flew exactly 1 hour under the same conditions on this test, then switched tanks, descended and measured the amount to fill.
Call it 194 MPH TAS, 4500' @ 8.9 GPH

At 140 Knots TAS @ 4500', 3800 RPMs and 28" MAP fuel burn came to 6.16GPH. I flew under the same conditions for exactly 30 minutes for this test. Conditions were a bit turbulent along the Cascade Mountains with a South wind blowing.
Call it 161 MPH TAS, 4500' @ 6.16 GPH

I am actually not sure how these numbers compare to Lycoming fuel burns at these speeds but I think these numbers are at least in the ball park and I believe they are very accurate.

I am very happy to finally have a smooth engine that is easily capable of busting VNE in level flight, keeps plenty of horsepower way up high, yet is showing what I feel are very acceptable fuel burn rates.

I can't predict how long it will last but at least it is putting in some very respectable numbers for speed performance and economy and it is truly a pleasure to fly behind.

Randy C
RV7A Turbocharged STI

Randy, those numbers are very much in line with the Lyc..

Randy said:

I did some more fuel flow testing today with what I think is a more accurate method as follows. I get stabilized at altitude, speed, and power settings, then switch to a full tank and carefully time the flight under those conditions, and then measure the amount of fuel required to fill that tank.

At 169 knots TAS @ 4500'. 3800 RPMs and 38" MAP measured exactly 8.9 GPH. I flew exactly 1 hour under the same conditions on this test, then switched tanks, descended and measured the amount to fill.
Call it 194 MPH TAS, 4500' @ 8.9 GPH

At 140 Knots TAS @ 4500', 3800 RPMs and 28" MAP fuel burn came to 6.16GPH. I flew under the same conditions for exactly 30 minutes for this test. Conditions were a bit turbulent along the Cascade Mountains with a South wind blowing.
Call it 161 MPH TAS, 4500' @ 6.16 GPH

I am actually not sure how these numbers compare to Lycoming fuel burns at these speeds but I think these numbers are at least in the ball park and I believe they are very accurate.

I am very happy to finally have a smooth engine that is easily capable of busting VNE in level flight, keeps plenty of horsepower way up high, yet is showing what I feel are very acceptable fuel burn rates.

I can't predict how long it will last but at least it is putting in some very respectable numbers for speed performance and economy and it is truly a pleasure to fly behind.

Randy C
RV7A Turbocharged STI

Click to expand...

You certainly have my numbers beat. At this altitude (why are you flying so low?) I'd be lucky to true 135 knots on 6.8-7 gph.

For the atmo guys here, the fuel flows stay about the same on a turbo engine at a given power setting so if Randy repeated the test at 10 or 15,000 feet the TAS would be a lot more impressive and the MPG figure would really pick up.

If you couldn't tell, i'm truly impressed with this. I'm wondering what a little turbo lyc could do properly tuned... Darnit, now I'm totally thinking about a custom engine to compete with this little beast. Keep us updated on the cooling as fairings go on, and summer comes up!

very nice

Randy,

Sounds like you are getting things dialed in pretty good. Those numbers are very good, maybe I better go get that turbo back

Steve RV-6 STI

Super Subie

Randy,

Congratulations Wow! that's one fine setup you have working. makes me proud to be working on my supercharged STI. Fast subie numbers are a welcome sight after some of the stuff i have seen posted.

airframe completion this week! glassed the windscreen today. installing the wings for the last time thursday. just a month or two of final engine setup, SDS installation, electronics testing and we be flying.

just curious, what are your boost numbers? amazing your MAP numbers, my lyc buddies will flip when they read your post.

thanks for all your help,

Had

Hadley said:

Randy,

Congratulations Wow! that's one fine setup you have working. makes me proud to be working on my supercharged STI. Fast subie numbers are a welcome sight after some of the stuff i have seen posted.

thanks for all your help,

Had

Click to expand...

Hadley, what's your supercharger and cooling configuration? SC from Egg? What driven pulley are you using; Egg-supplied or different? What's your radiators & oil cooler configuration? Congrats & good luck getting yours going.

brian

Cool

Lets repeat the test at 8000 DA (this will give a more direct comparison with how most of us compare performance.

Then do it at say 12k....Then it should be really impressive!

Frank

frankh said:

Lets repeat the test at 8000 DA (this will give a more direct comparison with how most of us compare performance.

Then do it at say 12k....Then it should be really impressive!

Frank

Click to expand...

The tests were already run at close to 8000 feet DA which is the typical cruise altitude for Lycoming RVs at around 75% power. The STI proved vastly faster even down here. At 12,000- 17,500, Randy can easily do anything up to 200 knots TAS at a very low power setting and fuel flow.

Ahh I just saw the previous post

rv6ejguy said:

The tests were already run at close to 8000 feet DA which is the typical cruise altitude for Lycoming RVs at around 75% power. The STI proved vastly faster even down here. At 12,000- 17,500, Randy can easily do anything up to 200 knots TAS at a very low power setting and fuel flow.

Click to expand...

Vastly superior?...Not so fast, I see a speed claim of 160kts TAS at 8000' DA on 8.5 GPH.

Thats pretty close to what I think my Lyc's 7a is doing..I.e 160kts TAS at 7 to 7.5GPH..Running LOP.

Now I say "think" cus since the early days of testing I honestly can't remember..I do clearly remember seeing 160kts TAS at 6.6GPH at about 13k'..I remember it because I thought it looked pretty darned good at the time..

Now I don't know how much power this blown STI is kicking out...considerably more than my IO360 I'm sure, And it is impressive, but the GPH for TAS figures still look a little better for the LYC running LOP.

So vastly superior?..well its faster for sure..More economical?..Not so sure.

And PLEASE don't take this as "car engines should not be in airplanes" mantra..Thats not it. I am very impressed with the time and dedication all of you converts (I was one too in my last airplane) have put into to making this happen.

I will be the first one to roll over and capitulate to a superior installation and may even fit one to my airplane when my Lyc wears out.

Sounds like some head to head flyoffs are in order.

Cheers

Frank

213 knots at 8000 is vastly faster than any stock bodied RV7A I'm aware of and this is using far less than anywhere close to even the stock hp output of this engine. I was talking speed here, not fuel flow. Stock MAP on the STI is about 57 inches and rated hp occurs at over 6000 rpm.

My main point is that 8000 feet is not the optimal altitude for this engine package. Randy was nice enough to run some tests down here to see how fuel flows compared at typical RV/ Lycoming cruse speeds. At any given power setting on a turbo engine, fuel flows stay roughly the same but TAS increases substantially with altitude. Conversely, to maintain say 180 knots TAS, fuel flow will decrease with increasing altitude.

There was never a question in my mind that turbocharged Subaru engines put out more power or could go faster than naturally aspirated Lycomings. Now with flight testing from Randy, it is clear that fuel flow vs. TAS is also competitive at medium to high altitudes.

While Lycoming installations are reasonably well developed, there is more to come from the Subarus. Randy has not experimented with leaning to any great degree and cooling drag could certainly be reduced from the present layout. I'd again note that no intersection fairings were fitted in these tests either.

Randy also validated how well MT propellers can work at altitude when they are not screaming at 2700 rpm. MT engineers had told me this a few years back- being much more efficient in the 2400-2550 rpm range.

If you want speed, the turbo STI clearly has it to the point one needs to be very careful at altitude with it.

Might be better

To be comparing this motor with an IO540.

The turbo/supercharger is an interesting idea, one could fit one to an IO360 I guess if the complexity or VNE overrun at altitude doesn't scare the pilot.

Frank

frankh said:

To be comparing this motor with an IO540.

The turbo/supercharger is an interesting idea, one could fit one to an IO360 I guess if the complexity or VNE overrun at altitude doesn't scare the pilot.

Frank

Click to expand...

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.

frankh said:

Vastly superior?...Not so fast, I see a speed claim of 160kts TAS at 8000' DA on 8.5 GPH.

Thats pretty close to what I think my Lyc's 7a is doing..I.e 160kts TAS at 7 to 7.5GPH..Running LOP.

Now I say "think" cus since the early days of testing I honestly can't remember..I do clearly remember seeing 160kts TAS at 6.6GPH at about 13k'..I remember it because I thought it looked pretty darned good at the time..

Now I don't know how much power this blown STI is kicking out...considerably more than my IO360 I'm sure, And it is impressive, but the GPH for TAS figures still look a little better for the LYC running LOP.

So vastly superior?..well its faster for sure..More economical?..Not so sure.

And PLEASE don't take this as "car engines should not be in airplanes" mantra..Thats not it. I am very impressed with the time and dedication all of you converts (I was one too in my last airplane) have put into to making this happen.

I will be the first one to roll over and capitulate to a superior installation and may even fit one to my airplane when my Lyc wears out.

Sounds like some head to head flyoffs are in order.

Cheers

Frank

Click to expand...

Frank,

I agree on the head to head flyoff. I have emailed Van's and offered to fly with one of the demonstrators, but I think they are way busy getting the RV12 stuff out.

I am looking for an opportunity to go fly with a 180 or 200 HP Lyc powered RV. I would like to fly around for a few hours, compare performance etc, then go fill the tanks and compare the fuel burns too.

I am near Seattle... at S36.

Randy C

Hey

This could work..I'm in Corvallis..Maybe we can meet in Arlington or somewhere


I got probably 185HP and a Sam James cowl, 7a

I'd love to do a side by side test and get some real comparisons

Frank

Frank
Sounds like we can do something. I sent you a PM.
RandyC

still amazed

what kind of boost pressure are you getting out of that turbo unit? keep up the great work.

Hadley,
The highest boost I have seen with the turbocharger was the 47" I had it turned up to when I hit that 213 knot speed at 8000'. There was more left but I honestly don't know how much.

The supercharger used to hit 52" at full power.

Randy C

Randy said:

I climbed up to 15,500' using 4400 RPMs and 40" MAP all the way to test sltitude...

The average came out at 184 knots, or 211 MPH. ...

I then went back up to 8000' and did a North and South run at exactly the same power setting of 4400 RPms and 40" so the fuel burn should be the same. This gave me an average of 162 knots or 186 MPH on 8.5 GPH, (assumed). I do not yet know for sure where 75% power is on this engine, or whether it really matters I know I can easily add more boost and or RPMs and hit Van's published performance numbers, especially at the top end...

On the way home, while up at 8000' I moved the power settings up to 4750 RPMs and 47" MAP. I accidently blew right through the VNE of 200 knots TAS ...

Randy C

Click to expand...

Randy, This is impressive indeed. Some of your results would be totally untouchable, at least by my old 200HP RV4. Seems fuel flow values for a given airspeed are similar to Lyc, as would be expected. (This is as much a measure of the airframe/propeller as it is the engine.)

Of course, carrying 40" of boost up to 15500 MSL is impressive in itself, but the result that really got my attention was your level blast at 8000'.

I do have one question, regarding VNE. I don't have an RV7, but are you *sure* the VNE is 200 KNOTS for that airplane? I ask because I've never seen Vans post airspeed limits in knots. Second, VNE for our aircraft should be INDICATED airspeed, not True. I only bring this into question because it touches squarely on safety.

---------------------------------

This is a remarkable effort that now has produced remarkable results. Good job!!!!!

Vne is listed as 230mph TAS for the 7s which is 200 Knots TAS.

With the turbo Randy is running he could theoretically hold 40 inches to 24,000 feet on a standard day. Turbine inlet temps and induction temps would likely be the limiting factors long before the turbomachinery reached its N1 limit however.

Bill Wightman said:

--snip--
Second, VNE for our aircraft should be INDICATED airspeed, not True. I only bring this into question because it touches squarely on safety.
--snip--

Click to expand...

I agree on the safety aspect, so you need to know that VNE is a TAS value, not indicated. See: http://www.vansaircraft.com/pdf/hp_limts.pdf

Bill Wightman said:

I do have one question, regarding VNE. I don't have an RV7, but are you *sure* the VNE is 200 KNOTS for that airplane? I ask because I've never seen Vans post airspeed limits in knots. Second, VNE for our aircraft should be INDICATED airspeed, not True.

Click to expand...

A while back there was an article in the RVator specifically addressing their concerns with turbocharging and/or putting bigger displacement engines in RVs. The article very explicitly stated that although in certificated airplanes the VNE can be read off the ASI, the flutter margins do reduce with altitude. Adding a turbocharger to an airplane will very easily allow one to exceed the flutter margins. In other words, flutter itself is a function of TAS, not IAS.

Here's the article. In my opinion it's a good read for anyone turbocharging or thinking about it. Heck, it's a good read for any of us. There's a great read in there about how Smokey experienced flutter in his normally aspirated RV-4 during a descent at 10,000 because he was looking at IAS and not thinking of TAS. Great read and I'm glad he shared his story with us.

After my experience in accidently busting through the 230 MPH VNE, I have learned to just watch my True Airspeed readout in the upper left corner of my EFIS, using 200 Knots as my speed limit.

It is really not that big of a safety concern, meaning that it is not at all hard to obey that speed limit. It is just important to know that 200 knots is 230 MPH and that TAS is the one to watch.

Too bad my VNE markings cannot be adjusted to indicate on TAS, but no big deal, I just need to pay more attention when I am taking pictures... I could see I was hitting a pretty good speed and got busy getting the camera out etc. before I realized just what that 213 number in the corner really represented.

After all the hard work I put in to the engine package to make it work, it is so cool to be able to report these kinds of performance results. I can't wait for some of the other folks with STI engines to get airborne and do likewise.

Randy C

Good Job Randy

Good job Randy indeed,
The "way to go" for normal aircraft is turbocharging. A supercharger not only adds the maximum boost concern but also a mechanical drive that must continously handle a high horsepower draw. The only plane that needs a supercharger is a propdriven fighter, and that plane will work just as well with a turbo! (P38 anyone?) Not to mention that it won't frighten anyone flying a F-22! Once properly sized for the application a turbo just works better and has less mechanical hassle. The other thing is it RECOVERS energy to improve efficiency, while a supercharger CONSUMES large amounts of HP to drive the compressor. You do need to have an engine that is designed to be blown to begin with in either case. The problem many people have is trying to use a car sized turbo which is usually designed to produce power quickly (at low RPM) and tends to overspeed in an aircraft. Several of the rotary conversions have tried to use the standard car turbo and while they continue to run they usually smoke the turbo after about 15-20 hours. The poor little car turbo is throwing exhaust turbine blades at nearly 100K rpms. Now that randy and Ross have sellected a proper size turbo Randy should get some long life from his combination. Cheers, and keep those numbers comming Randy! Bravo!
Bill Jepson

Rotary10-RV said:

Good job Randy indeed,
The "way to go" for normal aircraft is turbocharging. A supercharger not only adds the maximum boost concern but also a mechanical drive that must continously handle a high horsepower draw. The only plane that needs a supercharger is a propdriven fighter, and that plane will work just as well with a turbo! (P38 anyone?) Not to mention that it won't frighten anyone flying a F-22! Once properly sized for the application a turbo just works better and has less mechanical hassle. The other thing is it RECOVERS energy to improve efficiency, while a supercharger CONSUMES large amounts of HP to drive the compressor. You do need to have an engine that is designed to be blown to begin with in either case. The problem many people have is trying to use a car sized turbo which is usually designed to produce power quickly (at low RPM) and tends to overspeed in an aircraft. Several of the rotary conversions have tried to use the standard car turbo and while they continue to run they usually smoke the turbo after about 15-20 hours. The poor little car turbo is throwing exhaust turbine blades at nearly 100K rpms. Now that randy and Ross have sellected a proper size turbo Randy should get some long life from his combination. Cheers, and keep those numbers comming Randy! Bravo!
Bill Jepson

Click to expand...

Please give Ross the credit for choosing the correct turbo charger. I read three books on the subject, and crunched numbers for a week in an attempt to verify the selection Ross recommended. It is extremly inportant to get this right! In the end I went with what Ross recommended and it is working great. If you make an attmept at the excerise of choosing the correct turbocharger for an enigne for an airplane, it wont take long to see that it might be best to use what is working well for someone else with a similar airplane and a similar engine. It really is quite complicated, at least it was for me.

Reading all the stuff you can find on the internet about turbo selection will not help much either. Everything I could find related to cars or trucks, and they don't change altitudes like we do. That makes a huge difference and I think this is where the people trying car sized turbos get in to trouble.

I have seen some big mistakes made by some pretty well known engine bulders in turbo selection. Call Ross or someone else with a proven track record with aircraft turbo selection and save yourself some problems if you are trying to turbocharge.

I can now truly appreciate the difference in supercharger boosting and turbocharger boosting. Now it seems like the engine just runs free but still has the extra horsepower. It had plenty of HP with the supercharger, but it did have a noticeable drag on the engine, only noticeable after getting rid of it. Of course there are always drawbacks. I felt the need to place quite a bit of heat protective material in various places to keep that very hot hunk of steel from burning important items under the cowling. Also, the exhaust system becomes more important as it has some pressure to it behind the turbine and leaks / cracks could cause serious problems. My system is bit heavy but I am not worried about it leaking and cracking etc. None of the weight of the turbocharger should hang on the exhaust pipes.

Controlling boost with the turbocharger has been much much better than it was with the supercharger. Move the throttle and the boost goes with it. When you need to add more boost at altitude just open up the bleeder valve...

Randy C

The Wisdom of STI Experience!

Randy,

your numbers are super and well needed encouragement for me and my project. i thought about a lyc, many times wished i had made a different decision, cussed as the huge amounts of money flowed like water out the door. the research and parts to be nullified by the next expensive whistle, bell, drive unit etc.

and for the first time in a long time, i am truly excited about the STI potential again. i knew the engine had plenty of zip when jan and i ran her in florida, now it feels real to me. thanks for all your hard work and sharing your knowledge.

even though i have been playing the STI engineering game for 2 1/2 years now, i constantly realize i have plenty of STI catchup to do. you, Ross, John Ziggy and Robert are the only sources of actual data that i know of on this engine. you have actually flown this setup, something i have only dreamed.

so i completed my airframe yesterday and i am faced with a challenge. i don't like the factory m45 super, the hassle that now comes with the pulley change and the under powered super that it seems to be. (from what i gathered a miata unit that generates extreme heat). i might replace it.

i want no part of the heat that a turbo generates (did i mention how impressive your numbers are). currently, the way i am planning to setup my engine is with a centrifugal supercharger probably a paxton self lubricating. the consensus of the airport engineering team is a super is better, they used one on an F1 rocket and the plane is super fast. i live in texas and though i plan to do plenty of travel with my fast little, high flying rv, my home is HOT. we see 100F days sometimes for days and weeks in the summer.

i do enjoy your description and am beginning to get the picture. you said "I can now truly appreciate the difference in supercharger boosting and turbocharger boosting. Now it seems like the engine just runs free but still has the extra horsepower. It had plenty of HP with the supercharger, but it did have a noticeable drag on the engine, only noticeable after getting rid of it. Of course there are always drawbacks." those darn drawbacks. the wankel guy has some good supercharger/turbo points too.

i want a frictionless engine that burns no gas like the guy in "Illusions".

i want you numbers without the heat and of course without the tax a super puts on an engine. thanks, you described that well.

what turbo unit did you and Ross put together for our little STI if you care to share that data? any idea how many psi your getting out of that unit? how does that compare to the eaton i have? i am still learning to convert your high map pressures into something my brain can handle. i do love the looks on the airport faces when i describe your numbers.

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.

what is the most efficient cruise map or is that a function of density altitude?

which unit would be less taxing to the reduction drive?

that's all the questions i can think right now, i know i wrote a novel. its been an exciting day my wings are on for the final time.

keep those test numbers coming.

thanks again for all your help gentleman l look forward to your reply,

Hadley said:

what turbo unit did you and Ross put together for our little STI if you care to share that data? any idea how many psi your getting out of that unit? how does that compare to the eaton i have? i am still learning to convert your high map pressures into something my brain can handle. i do love the looks on the airport faces when i describe your numbers.

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.

what is the most efficient cruise map or is that a function of density altitude?

which unit would be less taxing to the reduction drive?

Click to expand...

The turbo Randy is using is a Garrett unit with TO4E -50 compressor, Stage 3 turbine wheel in a .82 exhaust housing. This is a sleeve bearing unit, not ball bearing.

Yes, the stock STI runs about 57 inches to develop 300 hp. Drag racing STIs run up to 120 inches. The Eaton supercharger is running over design limits on the Egg STIs. It is quite inefficient and produces a lot of heat at altitude as a result. Centrifugal superchargers are more efficient than the Eaton but there have been drive problems on many fitted to aircraft. The turbo is very simple by comparison and much more efficient at altitude and much easier to control boost with.

Randy is generally not running over 40 inches in cruise. Compressor efficiency exceeds 76% in the whole operating range and peaks at close to 80%.

The choice of blower types would not have an impact on gearbox reliability.

IMO, turbos are just overall a better choice on aircraft than superchargers. This is why all forced induction aircraft offered today are turbocharged.

sc vs turbo

Ross,

thanks for your input. your always a great help. we will finally be wiring your SDS in the next few weeks. i can't wait.

the unit cost for this turbo is much better than the sc. do you and Racetcech sell these or do i need to find a source? you can email me direct if you don't wish to discuss online.

still want all that heat to go away.

cheers,

Had

Sent me a PM and I'll give you a source in WA for the turbo parts. I have some of the other parts like the boost controller for cockpit control. I have a source in CA for the oil scavenge pump.

If the turbo is mounted low like Randy and Ralph Inkster, heat concerns are much reduced but you still need to watch the IR coming off the hot parts.

You'll need to upgrade the rads for your hot conditions like most of the other STI guys are doing now.

Heat is still there!

Hadley said:

Ross,

thanks for your input. your always a great help. we will finally be wiring your SDS in the next few weeks. i can't wait.

the unit cost for this turbo is much better than the sc. do you and Racetcech sell these or do i need to find a source? you can email me direct if you don't wish to discuss online.

still want all that heat to go away.

cheers,

Had

Click to expand...

Hadley,
I'm flatout going to try to discourage you from running the centrifigal supercharger. If you do it you will still have all the mechanical ills of the mechanical drive. Please note that the guys that built the Lancair with the supercharger had trouble with the mechanical drive on the supercharger at Reno! Check Thermal Solutions for turbocharger blankets to control in cowl heat. Please note the FASTEST sport class planes at Reno run TURBOCHARGERS. Even the Thunder Mustang has been converting to Turbo only. BTW you will need a intercooler for either system if you don't want detonation problems. The high boost used by the STI in auto use is rarely used for more than a few seconds. The drag on an aircraft is continous. The exhaust heat is still there on a supercharger application, and only a bit easier to control. The problem is that the higher you go the more the selection of a aircraft sized turbo becomes important. As I mentioned in a previous post the experience of the Wankel conversions is that the automotive boost device, Super or Turbo won't hold up. The most successful guys have gone to a larger compressor T4 based, I don't remember the trim numbers. The larger compressor keeps the system from over boosting. Another successful system using a 3 rotor went to an aircraft turbo from the start, flying in a Lancair ES with excellent results and over 200 hours to date with minimal changes. The proper aircraft waste gate is also important. Several auto turbos continue to make boost with the auto waste gate WIDE OPEN! The auto configuration never expects to see the level of continous exhaust perssure that the aircraft will have available. Commit to the aircraft turbocharger and you will not regret it.
Bill Jepson