Choices, Choices: SR22 Turbo or “Normally Aspirated”?

Being that Speed was one of my primary criteria for picking a plane, choosing the SR22 Turbo seemed like a no brainer.  Plus there is a lot of buzz around the SR22 Turbo and the idea of owning the “Turbo” of anything seems pretty appealing to me.  I had also read from COPA members that Cirrus is selling more Turbos than non-turbo (about a 70/30 split).  But I had a lot to learn about what Turbo means to an airplane engine.  My first clue that something is different about turbo airplanes was that both the Turbo and normal versions of the SR22 have the same 310 horsepower.  Huh?  In cars, a turbo engine almost always has another 50 or more horsepower, so what’s the deal here?  How could they have the same horsepower?

Then, I found this:

SR22 Turbo vs Non-Turbo Performance

This graph shows the performance of the SR22 Turbo vs. the Non-Turbo.  Seeing this graph totally blew me away because as you can see, the SR22 non-turbo actually OUTPERFORMS the SR22 Turbo below 10,000 ft Pressure Altitude.  That was a major eye opener for me.  I figured this data had to be wrong, but when I checked with the Cirrus sales rep, he did confirm the graph is accurate.  Below 10,000 ft pressure altitude, you can expect to get the same or better performance out of the non-turbo SR22.  Most SR22 owners don’t know that!  Even fewer Turbo owners know about the performance difference.

I don’t know the details of how it works (maybe a reader can fill us in with a comment), but essentially, in airplanes, a Turbo engine can perform like it’s at sea level altitude, all the way up to its ceiling altitude.  In the SR22 case, that’s 25,000 ft.  So a Turbo SR22 could climb between 15,000 and 20,000 ft the same way it would climb from 0 to 5,000 (that’s the idea anyway).  However, the extra weight and modifications to the engine to allow for the Turbo cause the sea-level performance of the Turbo to be significantly less than the non-Turbo.  It makes up for this shortcoming as the airplane gains altitude.  That’s way different than the performance improvement you can expect from a Turbo on a car.  Could you imagine if a BMW M3 only performed well when you were on top of Mount Everest?

So contrary to popular belief, there are significant disadvantages to the SR22 Turbo, including:

  • Worse performance below 10,000 ft Pressure Altitude
  • Higher maintenance costs and more things that could go wrong
  • Higher up-front cost (of approximately $60,000)
  • The Turbo engine costs an extra 50 lbs which is deducted from the useful payload

Plus, for the real benefits of the Turbo, you need to be at oxygen-required altitudes.  Although the SR22 Turbo GTS comes with built-in oxygen, I just don’t see myself or passengers ever wanting to use Oxygen for most of my travels.  I suspect that most of the time, I’ll be right at that 10,000 ft level, so my performance benefits would have been near zero.  My decision would have been totally different if either a) there was a pressurized cabin option or b) I expected to do most of my flying alone.  But knowing that I want to use the plane largely for business travel and with other people, Oxygen would put a damper on the whole experience.

And that’s how I selected the SR22 GTS, Normally Aspirated engine.

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24 responses to “Choices, Choices: SR22 Turbo or “Normally Aspirated”?

  1. Love the site! Very interested to hear your thought process, so I’m adding you to my RSS reader!

    I’m absolutely willing to be corrected in the following statements, however as I understand it, the reason normally aspirated engines decrease in performance at higher altitudes is that there are literally fewer gas molecules at higher altitude, oxygen – the main catalyst of combustion – being one of them. So, in very rough terms, the turbo basically compresses the available molecules to make the engine “think” it is at a lower altitude.

    What’s also interesting to note is that not only does a normally aspirated engine suffer at higher altitudes, but so does the wing and prop (a vertical, rotating wing). They’re trying to lift against gas molecules, and if fewer molecules are there, then the harder time they’re going to have generating lift.

    I apologize to any aeronautical engineers out there that just read my comment!

  2. Matt, I think you’re right on the money. That’s exactly how the turbo works, but the part that didn’t make as much sense to me was why the Turbo doesn’t perform as well as the NA engine at sea level. In cars, a turbo always beats a non-turbo. Shouldn’t that also be the case in planes?

    So the only explanation I could think of is that there must be some performance cost associated with the turbo itself and as you gain in altitude, the turbo makes up for the cost and then some (by packing in the air as you explained :-) )

    • For simple understanding, aircraft engines can operate at 75%+ power while just flying around below 6000 ft. unlike a car that rarely use more than 40% of its power at any given time and even less, 15%, while cruising. Being that an aircraft engine is most always working hard and designed that way, a turbo charger is then used as a suppliment giving the engine it full capability even after the air thins out as it climbs higher.

  3. Ah, I see your point. True; I’m not sure what the performance loss is all about. Odd.

  4. I think the difference between an airplane’s poor turbo performance at sea level vs. an automobile turbo, is that airplane turbos do not boost the intake pressure above sea level pressures, whereas an auto turbo does. Hence the auto turbo significantly enhances top horsepower at sea level. The plane turbo simply seeks to maintain the normal, non-turbo sea level horsepower, as it climbs above sea level. I’m not sure why a plane turbo is limited this way…something to do with maximum RPM on the prop, I would assume.

  5. Cirrus is turbo-normalized, which means manifold pressure is maintained at sea-level pressure. Therefore you won’t see any performance increase till 10,000 ft, when benefit of maintaining sea-level pressure overcomes the extra weight penalty of turbo-charger.

    In the Columbia 400, the turbo-charger boosts pressure beyond sea-level, so you can see substantial performance improvement over Columbia 350 (normally aspirated), even from sea-level onwards.

  6. very interesting, but I don’t agree with you
    Idetrorce

  7. Nothing comes for free. A piston engine is essentially a pump. When the exhaust exiting the engine drives the “hot” side of the turbo it is taking energy from the “pump”, the engine. This is a fairly small loss, but is a source of some loss of power. Also, as the incoming air is pressurized by the turbo it is heated a great deal, often in excess of 100 degrees. In an air cooled engine, hot intake air causes excessive heat and reduced detonation margin in an engine that is already heat stressed. Hot air containers fewer air molecules compared to cold air at the same pressure.

    In an effort to fix this problem, the incoming air is greatly cooled through the use of an intercooler. However, pushing the air through radiator like device causes even further pumping losses. So, yes the naturally aspirated engine will produce better performance to a point.

    Note that in the graph only 85% of rated power for the turbo normalized engine is utilized. In fact, if you wish to produce 100% power, the turbo normalized engine will do this for you. Though fuel burn would be high, at 5,000 ft or so the turbo will begin to pull away from the N/A engined plane.

    If your mission is flying over the 1/2 of the U.S. that is relatively flat there is no compelling reason for the turbo. In areas of high mountainous terrain the ability to efficiently climb and cruise above the terrain and weather is a great advantage.

  8. no se puede comparar un auto a un avion,a 18.000ft hay la mitad de oxigeno que a nivel de mar,ahi es donde es mas eficiente el turbo al mantener el aporte constante de oxigeno al motor.Los autos siempre circulan dentro de un rango normal de altitud,si a su auto normal le saca el tubo de escape y el filtro de aire le funcionara parecido a un turbo.

  9. Hi,
    i am so mcuh confused dont know either to go for turbo or non turbo, i normally go for mountain flight, and havent yet got cirrus , wish to know is cirrus turbo is a preassurised or non preassured, cause normally i am always on 18000 at, if i could get some hint about the cuirrs

  10. The Cirrus Sr22 Turbo is a turbo normalized engine with some pretty tight tuning. I have a great deal of time in both versions of the SR22 and I feel the Turbo is wonderful. It is nice to cruise above 10,000 feet. There is no traffic. Everyone is required to have a transponder(this is good when you have traffic alert). The turbo climbs so much stronger and you only need to go to 8000 ft usually to notice a difference in trip times. How? The turbo holds a faster TAS through the climb than the non-turbo.
    The turbo-normalized engine is so much easier to fly. One mixture setting..thats it! I sum it up by saying “In a Cirrus Turbo below 8,000 you use less fuel than a non[turbo Cirrus, and above 8,000 you go faster. That 8,000′ number changes with temp and altitude. I agree with the more maintenance point. There are more parts to maintain and a higher level of tuning.
    Cirrus Turbo Advantages: Speed, Ease of operation, OPTIONS in weather.
    Disadvantages: More parts to maintain
    I wouldn’t recommend a new pilot get a Turbo because they typically do not have the flight profile to enjoy the benefits. It is easier to fly though. Good Article!

  11. Made it coast to coast (KSMO to KSRQ) with one fuel stop in Texas, a little over 8 hours total time. Top GS was 294 kts. New G3 Turbo Perspective. N622CT. Flew at FL 250 until O2 ran out.

    SWEEEEEET…..

  12. Has any one had a problem with detontation in the Cirrus SR22 non-turbo? We had a cylinder g0 down due to detontation.

  13. The M3 has never had a turbo. And never should in my opinion.

  14. I would have purchased the Columbia due to the fact that it’s a non normalized turbo. Just me.

  15. Ok. the reason its turbo normalized is so it doesn’t put anymore stress on the engine. You would have to make the engine parts thicker to be stronger, thus heaver. So you really need to redesign the entire engine. However, with the turbo normalizer, you’re making it AS GOOD as sea level, but not any more powerful, thus you don’t need a more powerful, heavier engine. Its brilliant!

  16. One reason the turbocharged engine produces less power below 10,000′ is that it uses lower compression pistons than the non turbo.

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