Different Strokes

Come on Rick, Don't hold back; Tell us how you REALLY feel.
Mel...DAR

The Mighty Roar..........

Rick6a said:

.....Time for cucumber sandwiches, rice cakes, and Oolong tea.

Rick Galati RV-6A "Darla

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.........and time to go get my copy Yoga Times and the Utney Reader.......

buckle up

Rick: Talk about taking the first punch. This thread ought to be interesting. Were you just bored, now that you are flying? you probably need to get another project going. I bet when you were a kid you liked starting fires. with auto gas no doubt.

Rick,
I'll bet you put playing cards in your bike spokes for the "masculine" sound, didnt you?

Funny when I get down from a flight in my turbo Sube RV6A, most people say something like " **** that thing sounds great". The Lyc powered RVs sound just like another 172 without a muffler. Snor.... A Merlin sounds really good, especially a 3000 hp one at Reno running 130 inches at full rpm, a 6 cylinder Cont or Lyc sounds good, a 4 cylinder Lyc is not my idea of a good sound. Kinda sounds like something's wrong inside- like a Harley- well not that bad maybe.

Hey rv6ejguy,

What do you cruise at and what fuel flow. I have an IO-360 cs, and I consistently cruise at 170KTS TAS at 8.5 Gal/hr. I've got the impression from a lot of Sube drivers that they are cruising at only around 150kts, and to get it up to 170-180kts range really burns the gas. Is this true from your experience? Just curious.

Tobin

tobinbasford said:

Hey rv6ejguy,

What do you cruise at and what fuel flow. I have an IO-360 cs, and I consistently cruise at 170KTS TAS at 8.5 Gal/hr. I've got the impression from a lot of Sube drivers that they are cruising at only around 150kts, and to get it up to 170-180kts range really burns the gas. Is this true from your experience? Just curious.

Tobin

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We do 155-170 knots TAS depending on altitude. Leaned to 1450F we are showing 9.2 gal./hr. Still don't have a good rad set up and the engine is under propped at higher altitude. With an MT and a belly rad, we'd be up 5-10 knots. We use a programmable ECU so we can lean however we want. Not locked into the OE AFRs as the Egg Subes are for instance. My friends -6A with O-360 C/S is a few knots faster below 10,000 feet as well and burns just a bit more than me. I got the turbo whistle though!! Way cool!

Do you run with the EGT's at 1450 oF very often? I'm just curious here (maybe a tad ignorant too). Is that measered TIT (turbo inlet) or exhaust? If it's the Turbo inlet isn't that kind of high? Typically, bad things start to happen to most engines with EGT's of 1500oF +.

Of course, I don't know much about subies, so that's why I'm asking. I'm just curious here!

Thanks for the info, it's nice to see the numbers you posted.

Cheers,
Stein.

These are EGTs. We used to lean to 1400F on the hottest cylinder. After installing a wideband AFR meter, we felt safe leaning further to 1450F. This is an AFR of around 13.8 to 14.0 to 1 so slightly rich of peak. Since there are no published limits on this, we are conservatively approaching peak operation and writing the book as we go. So far no engine problems in 150 hours.

Most aircraft engines can be leaned to 1550-1650F so 1450 does not seem to bad on a liquid cooled engine. The EJ22T has forged pistons and oil squirters under the pistons with 5 main bearings and forged crank and rods plus a die cast case. It is a very robust design. If we can eventually lean to peak and around 1500F, we expect fuel flow to drop another 6%. SFC is around .42 right now so that would drop us down to .39 something. With the EFI, we might even be able to go LOP which would maybe worth another 5%. Compression ratio was raised to 9.45 to 1 to increase thermal efficiency.

Great! Thanks for the numbers. Those are the kinds of posts I like to read. Facts, not speculation! I appreciate you taking the time to share it.

That being said, I've been working on these old airplane engines a long time, and IMHO wouldn't readily recommend that anyone routinely lean to "1550-1650" degrees on a regular basis without VERY accurate multi cylinder EGT/CHT measurements, etc...along with a good understanding of what they are doing. Exhaust valve reliability in auto as well as AC engines goes down at extremely high temps. I think you'd find that running your engine constantly near 1600 degrees will result in bad things happening, liquid cooled or not.

In your installation, I'd be less concerned with basic EGT's and more concerned with the turbo inlet temps.

Anyway, I was just looking for info and appreciate your response. Please do keep us posted as to your progress.

Cheers,
Stein.

With a turbocharged engine, automotive experience suggests you should target an A/F ratio closer to 12:1 than 14, even at low boost levels. The EGT is too slow to protect a lean burning engine under power, particularly if you happen to get some bad fuel or encounter a timing glitch.

The turbo inlet temps are irrelevent. Turbochargers are designed to convert heat to generate the energy to compress air; they typically drop eshaust temps 300-400 degrees. To protect your motor, Id recommend a wide-band O2 monitor and fuel pressure guage over an EGT.

cobra said:

With a turbocharged engine, automotive experience suggests you should target an A/F ratio closer to 12:1 than 14, even at low boost levels. The EGT is too slow to protect a lean burning engine under power, particularly if you happen to get some bad fuel or encounter a timing glitch.

The turbo inlet temps are irrelevent. Turbochargers are designed to convert heat to generate the energy to compress air; they typically drop eshaust temps 300-400 degrees. To protect your motor, Id recommend a wide-band O2 monitor and fuel pressure guage over an EGT.

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We have narrow band, wideband and a four probe EGT in the aircraft for mixture monitoring. Contrary to web scuttle, my experience of 25 years of building turbocharged race engines and running them on dynos and the race tracks show that best power is made at 13-13.5 to 1. Reliability is in no way compromised running at this AFR. Indeed, testing in the aircraft with the wideband confirmed best speed and highest engine rpm occurred on this Sube at 13.4 to 1 AFR, EGT was 1320F. 13.8 results in around 1400F, 14.2 gives us around 1450F.

Turbos do indeed care about inlet temps. Garrett sets continuous limits of between 1600-1650 for most models fitted with Inconel wheels. We find a drop of 180-200F across our turbine wheel at cruise power settings.

Flying the geared turbo Lycs in P Navajos, found peak ITT at around 1600-1625F which is fine according to Lyc. Many pilots were more comfortable cruising at 1550F however. This was before GAMIs were available of course. Now LOP operation seems to be the way to go for these types of engines.

"The EGT is too slow to protect a lean burning engine under power, particularly if you happen to get some bad fuel or encounter a timing glitch."


The fuel comment is particularly good. When I was racing we used fuel delivered in sealed five gallon drums straight from VP, Phillips, or whatever, because it was of known value. Once we unsealed the can, at the end of the day the reamining fuel went in the town vehicle. At very high specific outputs a little stray alcohol or some other oxegenator can ruin your day.

The idea of running those sort of temps in an amature built turbo charged aircraft setup scares me silly...it is enough to make stainless steel start getting "plastic" which is why the impellers are iconel in the first place.

As for temps not being an issue for a water cooled engine...BS...the exhaust valve in particular still must transfer heat to a guide, to the head and to the water and oil. Even porsche, in their water cooled, turbo racers, went to custom sodium filled stainless valves when they ran the outputs being discussed. They also replaced them every race weekend.

Of course there is a chance that they didn't know what they were doing....they after all have the reputation of being wreckless engineers..;-).

I didn't say, or mean to imply that head temps were unimportant- I said turbo inlet temps are unimportant when the mixture is controlled correctly, or in other words, the mixture/timing are the issues to watch. The turbo likes heat as long as it does not damage the equipment (too lean, too much advance, or too high boost levels, etc).

I personally think running a turbocharger (or any high compression system for that matter) with a fuel/air mixture 13.0:1 or higher is asking for a meltdown eventually should one of the variables get out of range. The 12:1 ratio I suggested provides a small safety margin without hurting power significantly. Running slightly lean does produce more HP, and a lot more heat- it is a question of balance and engine durability. It is what I target on my twin-turbo Mustang without problem and, to me, you should err on the safe side with aircraft.

Jconard said:

"The EGT is too slow to protect a lean burning engine under power, particularly if you happen to get some bad fuel or encounter a timing glitch."


The fuel comment is particularly good. When I was racing we used fuel delivered in sealed five gallon drums straight from VP, Phillips, or whatever, because it was of known value. Once we unsealed the can, at the end of the day the reamining fuel went in the town vehicle. At very high specific outputs a little stray alcohol or some other oxegenator can ruin your day.

The idea of running those sort of temps in an amature built turbo charged aircraft setup scares me silly...it is enough to make stainless steel start getting "plastic" which is why the impellers are iconel in the first place.

As for temps not being an issue for a water cooled engine...BS...the exhaust valve in particular still must transfer heat to a guide, to the head and to the water and oil. Even porsche, in their water cooled, turbo racers, went to custom sodium filled stainless valves when they ran the outputs being discussed. They also replaced them every race weekend.

Of course there is a chance that they didn't know what they were doing....they after all have the reputation of being wreckless engineers..;-).

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Well back to this again!

Hey, we're doing it and have 155 hours on the engine with no evidence of anything going away so far. I've been doing high output turbo race engines for 25 years and they don't blow up. Most of the heat from the exhaust valve is transfered through the seat to the head, not to the guide on auto engines. See the small stems used on auto valves compared to air cooled aircraft engines. This is why we grind the seats a bit wider on turbo applications. I have never melted a standard exhaust valve in any of these turbo engines.

Tests on exhaust valve temps by Wright show that standard valve ran at around 1250F with sodium cooled valves running about 100F cooler. This is nowhere near the plastic limit of stainless. If it was, these valves would fail in a few hours.

Impellers are a non technical word for compressor wheels. Compressor wheels are made of aluminum alloy in most cases (cold end). Turbine wheels are made of high temperature alloys like Inconel, Stellite, MAR-M 247 etc. This is the hot end. A turbine wheel is not an impeller.

We don't see issues with fuel variations running Esso 100LL. EGT vs. AFR agreement is within 20F at the same power setting from day to day. With auto fuels, you certainly could have variations like you speak of.

While all this theory is great, like the bee that doesn't know it shouldn't be able to fly, we are running the Sube and Garrett at these temps. Others like the Clarke brothers in their Dragonflies have over 1000 flight hours on turbocharged Subes running similar setups and temps. To my knowledge, they were not burning exhaust valves. There is a big difference between sitting in your chair saying it won't work and flying the thing and seeing that is does work. I think that's why someone thanked me here for posting REAL data, not conjecture.

rv6ejguy,
Its fun conversing with another turbo junky. Which Garrett turbo are you using? How much boost? What waste gate controller?

From your comment, I assume you normally use 100 octane fuel with your Subaru? That should make a difference in the tempertures the system can safely withstand.

I know several gearheads who have destroyed engines running too lean (14 range) periodically (as in drag racing, ~10 second/runs) at 12-15psi peak boost levels (700+ HP). My other toy, a 5.0l Mustang daily driver (twin small, but efficient, Garret GB35's- 2 ball bearing races, oil/water cooled) geneates 450+HP/500 ftlbs @ 8psi with 91 octane fuel and conservative custom tune; it never overheats, but it does have larger injectors that keep the A/F mixture in check at full throttle. The slightly richer mixture helps keep combustion temps down with full ignition advance.

FWIW, I wouldn't think engine damage would come from valve failure or seat erosion, it would come from heat related detonation that has a nasty habit of melting holes in cast aluminum piston and breaking ring lands. The high octane fuel you are using helps a great deal to control detonation at elevated heat levels.

My Sube has JE forged pistons which I designed, raising the compression from 8 to 9.45 to 1. We burn exclusively 100LL because of this and its better vapor lock resistance at altitude, plus I'm not hauling fuel out to the aircraft.

We run a max of 40 inches Ab for takeoff, 35 for climb, 30 for cruise.

Currently using a T3 with TO4 E50 compressor, stage III turbine wheel, integral wastegate, with cockpit adjustable air controller, .82 A/R turbine housing, sleeve bearing with a dry/ dynamic center section. Was intially fitted with a Super -60 T3 compressor. Don't notice much difference below 10,000 feet between the two.

The relatively lean mixtures don't cause damage directly but if you are on the edge with timing vs. octane, pre-ignition or detonation is more likely which can cause a near instant failure, especially with cast pistons. We have run timing experiments in flight with the SDS programmable EMS. The engine performs best with 32 degrees of total timing.

Cobra, glad to see that someone else here likes turbos. Your Mustang sounds like fun!

I've had zero maintenance issues with the setup using slip jointed 321 stainless headers.

Rv10 Ls V8

Here is a new player in the field http://www.v8aircraft.com/. These guys have done a very clean conversion on a Seabee which has been flying since 2000. Claim 1500 flight hours to date. Use OE ECU. About $30,000US for new engine, redrive, ECU etc. Extra for mount and other options. Can drive hydraulic prop I think.