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Old 07-18-2005, 01:41 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
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Location: Calgary, Canada
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Default Sube vs. Lycoming

In a recent, side by side test, Robert Paisley's Eggenfellner Subaru STI powered RV7 was able to pull past Dan Checkoway's very fast 200hp IO-360 powered RV7 despite Robert's plane having a heavy passenger and Dan's plane having an empty seat. Another myth put to rest now that the Eggenfellner Subes can't keep up with the best Lycomings.

Last edited by rv6ejguy : 07-18-2005 at 01:47 PM.
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Old 07-18-2005, 02:01 PM
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Kahuna Kahuna is offline
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Default Oh Dan say it isnt so.

Did you hold back for pitty?
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Old 07-18-2005, 05:48 PM
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dan dan is offline
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Default It's true

At first he had 2 knots on me, but I messed with mixture and was able to achieve the identical GPS groundspeed, flying side-by-side. But like it was mentioned, he had a heavy passenger onboard. He would take me if all else was equal.

But that's at 8500', density altitude of maybe 12000' due to high temps. And presumably any altitude higher than that, he could easily pass me.

We didn't compare fuel burns, but it would have been interesting.

I think after OSH, Robert and I will go up and do some side-by-side testing at lots of altitudes and seriously record all the parameters. Specifically fuel burns, relative true airspeeds, etc.

I suspect I will be able to take the Subaru setup with my 200hp IO-360 at altitudes UP to about 8000' which point the Subaru will probably start kicking my butt. But I also assume it will come with a price, that being higher fuel burn.

But let's go do some testing and see exactly how it plays out.

)_( Dan
RV-7 N714D (560 hours)
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Old 07-18-2005, 06:30 PM
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gmcjetpilot gmcjetpilot is offline
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Unhappy Dan Dan Dan Dan, tell me it was all dream

Oh my Gosh, the Subie Guys are going to be more out-O-control.

Good for Robert Paisley's, congrats. Uhaaa I would love to hear from Robert on what improvements he might have made or not made over a stock Eggie, what kind of prop did he used?

Actually this is not new news. Usually the turbo Subie will start to give an advantage only around FL100 to FL120 and above. This was proved out in a Custom turbo Subie vs. Lyc side by side fly off.

From what Dan stated it sounds like the speed was matched at DA of 10,500-12,000 feet. That is to be expected. It would be interesting to take it up even higher. I wounder it there is TIT (turbo inlet temp) limit?

As far as Gross weight factor: According to Van's aircraft specs, solo weight vs. Gross weight is worth (1) MPH. So that is not an issue.

So for the Subie to do "Butt Kicking" they would need to fly above 10,000 -12,000, if kicking butt means a matched or 1-3mph.

Flying high is great if you plan on flying at that altitude and using O2 to get the advantage of the Turbo. If Dan where to turbo/intercool his Lyc than we would have a different result. It is not as much as the Subie is making more HP it is more that the Lyc is loosing HP. From the charts Dan's Lyc was around 65% or 130-122hp. (Of course no one mentioned RPM?)

I flew turbo'ed Lyc's before at FL250 in a TS Aerostar TS61. It was a mid-wing twin with turbo/injected Lycs (6 cyl). This model was not a pressurized, so this is where I grew to hate sucking O2 from a mask or cannula. Flying at FL100-FL120 all day without O2 can give you a headache.

Any way not to take anything away from Robert's turbo charged Subie powered RV-7, but it is now time to do some real side-by flight testing and get real comparison with all the numbers: RPM/MAP, weights, temps and fuel burn.

I like the side-by-side comparison, which is great way to level the field. The way Van compared two factory Demo RV's to two Rotary powered RV's was interesting. (In this test the 200 hp Lyc was slower than the 180 HP lyc, no doubt due to the fact the 200 HP lyc was tired from a few thousand demo flights. Also the Rotarys had a very slight edge, but burned huge gas doing it.) To determine the fuel burn Van's test started with full tanks and after flying a set course, landed and refilled, comparing use like we do with our cars. Also a side-by-side climb test was interesting. This is just the kind of thing the Cafe Foundation should be doing.

Oh boy Dan we will never hear the end of this. Cheers George

Last edited by gmcjetpilot : 07-18-2005 at 07:34 PM.
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Old 07-18-2005, 07:33 PM
cobra cobra is offline
Join Date: May 2005
Location: Utah
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The issue between the two is not HP- it is torque. The Lyc has more displacement and a long stroke- much like a diesel engine. The Lyc generates significant torque at low engine speeds, which falls off rapidly as rpm increases.

The Subi is a smaller engine with a short stroke and limited torque output; it converts high rpm HP to the needed torque levels through a reduction drive.

I suspect the Lyc has a significantly higher fuel burn rate because it is less efficient (wastes energy generating friction, vibration, and heat). The Subis have a big advantage in smooth operation, durabiity, and part replacement costs.

BTW, head to head speed comparisons are a terrible way to comapre engines- there are way too many variables involved. The only reliable comparison would be to test both engines in the same plane, same prop, or tested on the an engine dynometer under identical conditions.
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Old 07-18-2005, 07:34 PM
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rvatornate rvatornate is offline
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Actually, Robert's Sube is not normalized. It makes its max power at sea level just like the LYC, it looses power at the same rate in the higher altitudes just like the LYC. Robert has the STI engine from Subaru/Eggenfellner. It is designed for max HP at all altitudes. The 2.5l single cam that Egg also sells is normalized. In other words, it's max MP is 34 inches, and it can sustain that to somewhere in the 14,000 foot range. Robert's supercharger is maxed out at 50 or so inches at sea level, and drops off at the rate of 1 inch per 1000 feet just like the LYC There is no doubt that the 2.5l with the normalizing supercharger gains power relative to a normally aspirated LYC as they climb, but that is not the case with Robert's engine as I understand it.

Nathan Larson
310 hours on Egg/Sube 2.5l single cam normally aspirated. Looking forward to learning more about Robert's engine at Oshkosh
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Old 07-18-2005, 08:00 PM
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gmcjetpilot gmcjetpilot is offline
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Default I disagree

Originally Posted by cobra
I suspect the Lyc has a significantly higher fuel burn rate because it is less efficient (wastes energy generating friction, vibration, and heat).
Uhaaa you are guessing, no one reported FF, MAP or RPM, and you are correct, all you can do is suspect. However I disagree that the Lyc is burning more gas. From the Lyc IO-360 (200hp) power chart, fuel burn, best power @ 2600 RPM at 65% is around 11 gph. From a Turbo subie was measured at 70lbs/hr or more flat out, or approx 11.7 gph (at high pwr @ 5,000 ft, 14 gph was recorded). There is no free lunch, and stroke and torque has little to do with it. You need so much thrust to go and that cost gas. A Subie is an internal combustion engine folks. Electronic fuel injection, overhead cam 4-valves and water cooling is more for car issues and of only little advantage in an airplane at constant power. BTW in a diesel , fuel efficency comes more from the high compression than stroke/displacement (piston dome and positive displacement supercharges).

Originally Posted by cobra
BTW, head to head speed comparisons are a terrible way to compare engines- there are way too many variables involved. The only reliable comparison would be to test both engines in the same plane, same prop, or tested on the an engine dynometer under identical conditions.
I disagree there are no excuses and heads up is a tried and true way to test and eliminates variables. Who cares what a dyno says, as installed in actual conditions is the best way. Real performance not numbers. Also it is hard to get the same airplane, but the consistency of RV's from accurate kits is pretty equal. Dan's RV is nice but unpainted. If it was panted and waxed it would go 2 mph faster (verified by the cafe foundation BTW ). Installation and props is the main part of the issue. I always said the draw back of the Subie is electric props (required) and poor cooling drag from work around heat exchanger installation. Installation is every thing, form, fit, function, weight, systems are all relevant.

With variation in the atmosphere testing in the same place at the same time is fair and accurate. With out side-by the Subie's small advantage would not be possible to detect, because measuring TAS with in a few mph with GA instruments is more than the tolerance can allowed. Are you scared? "Heads-up or shut-up" is what they say at the track. Right now the Subie has the bragging rights, so let the games begin (fun). By the way I like Subies and this is all in fun, but lets move the discourse further than beating the horse over again about opinion and preference.

Originally Posted by cobra
The Subies have a big advantage in smooth operation, durability, and part replacement costs.
This has nothing to do with performance and is subjective. The cost of a new O-360 has dropped over $4,000 over the last few years due to the clone market. Lets just talk performance. A turbo Subie Eggy kit engine is way more than a Lycoming to purchase, so let's not go there. The cost of owner ship is only a guess at this time. All I know is I flew my light twin everyday for 3 years and never did any thing other than oil/filter changes and plug cleanings. After three years I sold the plane for more than I payed for it. Sam with my RV-4. My O-360 core I just overhauled for my RV-7 cost me a total $13,000 with dual elec ignition. What does a total Eggy set up cost? What is the resale of Subie RV's vs an O-360 Lyc RV? Again cost of ownership and smoothness are subjective. Side-by performance is not subjective.

Yes auto engines can match or get a slight speed advantage at altitude but they are working real hard (high RPM and MAP). A Lycoming is rated at 100% with no limitation except CHT/OIL Temp. Not that Dan's plane is slow, but with a Sam James style cowl and sealed cooling pressure plenum his RV-7 would go up to 10mph faster. Cooling drag is an issue the water cooled engine crowd must address. The URL I referenced twice above is an example of a builder really experimenting with different ideas, including a fuselage radiator. Worth a look. I would love to see how fast his RV-6 Subie turbo (big turbo with intercooler) is against Robert's RV-7 Eggy Subie.

Cheers George

Last edited by gmcjetpilot : 07-18-2005 at 10:29 PM.
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Old 07-19-2005, 12:33 AM
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Default Robert's engine

Robert's engine has a supercharger, not a turbo. I believe the prop is the MT Propeller MTV-7 - at least that's what Eggenfellner delivered with my STI engine.

From what Robert posted on another list, the main work he has been doing on the installation is to improve the airflow efficiency through the cowl.
Mickey Coggins
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Old 07-19-2005, 12:51 AM
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rv6ejguy rv6ejguy is offline
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My original post was merely to inform of the progress being made by Eggenfellner and Robert on the supercharged STI package. Robert's RV7 uses an Eaton supercharged Subaru 2.5 with a barometric controlled compressor bleed system. This is quite a different animal from a turbocharged engine. Robert has done some experimentation with radiator ducting and cowl flap modifications plus some testing on the intercooler setup.

Racetech owns the Turbo Sube 6A GMCJETPILOT refers to here which is held back from performing better by the IVO propeller currently fitted. This prop is unable to absorb even modest power (over 30 inches/ 4600 rpm) above 10,000 feet. If we were willing to spend the money on an MT C/S, we have no doubt that this aircraft could exceed 200 knots+ TAS at fairly low power settings. Currently top speed is 182 knots TAS running 34 inches/5000 rpm 15,000 feet with the IVO at full coarse pitch and quite unhappy. There is much conjecture on how good/ bad the IVO is working with this combination of redrive ratio, airspeed and pitch and whether the airfoil is well matched. Only way to tell would be the fit a different prop and see. Our cowling radiator setup has high cooling drag in our view as well which is why the new RV10 project will use a P51 style scoop. For the time being, we use the 6A as a testbed for the SDS EFI, redrive, turbocharger testing, cooling system testing plus staying current. The lessons learned will be applied to the -10. We'll continue to improve all aspects of the Subaru installations just has Eggenfellner has with his as we learn more.

The Egg Subes tend to have relatively high fuel flows at high power settings due to the use of the OE ECUs and the fact that they jump into open loop mode at relatively low power settings. The default air/fuel ratios (AFRs) in open loop are around 13.0 to 1. Recently, Egg has added a new fuel pressure regulator to drop baseline fuel pressure and leaning the AFRs in open loop to lean the mixture at higher power settings. This appears to be working although there are unknowns with the self learning features of this ECU and whether the AFRs will be eventually return to what Subaru intended. Testing will soon prove this out.

We currently feel that the frictional losses are relatively higher on a Sube turning at 4500-4900 than a Lyc at 2600 rpm. This negates some of its advantages in the fuel flow department. The RV10 will use a different redrive ratio and an MT C/S prop in an effort to get cruise rpm down to about 4000 rpm where volumetric efficiency is highest and SFCs are lowest. We also raise the compression ratio to the 9.5 range to boost thermal efficiency. We hope to recover more work from the turbos to reduce pumping losses by cruising at lower rpm and higher manifold pressures. Current leaning experiments have not been carried to peak EGT or LOP operation at this time as no one has previous experience running these engines under boost in cruise. With EGTs currently limited to 1450F, we see the SFCs similar to a Lycoming. This represents an AFR of 14.2 to 1 so there may be 10% improvement in SFCs possible. Our current feeling is that a turbocharger is superior to the Eaton type blower for power, reliability, fuel flow and noise reduction however many might disagree. Both have been shown to work well and I welcome further testing of both strategies.

We feel that side by side testing is the best as there are too many variables with cooling drag, altitude performance, exhaust thrust and propellers to do useful terrestrial testing. I'd have to agree with GMCJET here.

GMCJET is right, sucking on O2 is a drag. While the RV10 will have built in O2 and the turbos will be well matched up to 18,000 feet, we want equal or better performance to the IO-540 installation in the normal realm of 8000-12,000 feet cruise altitudes. If we decide to use the nose tubes, we expect to see 190-200 knots cruise at 75% and 18,000 feet.

As far as these engines working hard, no. The piston speeds are actually lower on the Sube so 4600 is no harder than a Lyc at 2700. The STI 2.5 and EJ22T are engineered to operate under boost for extended periods with piston oil sprayers, stronger pistons, pins and blocks. The basic longblock has been shown capable of making over 900hp for short periods at over 100 inches hg Ab and 8500 rpm. Cruising at 150 hp is far below any critical stress levels. Of course there are coolant temp, oil temp and EGT limits just as on any engine.

As a sidenote I've observed a few cases now of 180hp O-360s, outperforming 200 hp IO-360s on several RVs now. What is up with that?
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Old 07-19-2005, 01:02 AM
cobra cobra is offline
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Hey George,
I always enjoy your counterpoints. My only comment regarding plane to plane comparisons is that (I understand) at full power, top speed operation, the aerodynamics of the specific planes have more effect on top speed than the engine/prop combo does. The plane is near a point of fast diminishing returns as far as speed is concerned. I suspect that pilot skill is every bit as important there too. How else can you explain the race result differences from seemingly identical planes with identical motors/power ratings.

I fully agree with you that various engines produce similiar power/ fuel flows when they operate at PEAK output. My thought is simply that the Lyc is closer to full power output at 2300 rpm than the Subi would be at 4500 rpm- the Sub is still building up to its peak. BTW, the Subi should be good for more power thru tuning than the Lyc, simply because it is capable of higher RPM- we only need to flow a little more fuel and air through.

Ive been kicking these ideas around wondering what effects might be expected from mounting a Mazda Renesis rotary in a 7A (capable of 250+ HP in a lightweight package). Im guessing faster climb rates, maybe a little more load capacity, but not a whole lot more top or much faster cruise speed than the 200HP setups. I like the Renesis because it is newer and refined, more efficient, and quieter than earlier rotaries were, not so much for the extra power on tap.
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