IO-550 Upgrade: real-world performance improvements

Martin Pauly

Martin Pauly

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Martin Pauly
I've flown 35 hours since the engine upgrade in my A36 Bonanza - the break-in is far behind me, so it's time to analyze the real performance changes. And I attribute those changes to three things:
  • Upgrading from the IO-520BB to the more powerful IO-550B
  • Changing to a modern, more efficient propeller (Hartzell Scimitar)
  • Replacing the old equipment with brand-new items
I cannot provide an allocation of the total performance improvements to these three contributors, but I can tell you my typical cruise speed has improved from 155 knots to 167 knots (true airspeed) at 20 degreed LOP.

In this video I summarize the first time I took the new configuration up 10,000 feet and cruising at lower-than-break-in power settings. In the process, I determine the GAMI spread, which was surprisingly good given that I am using stock injectors from Continental (0.2 GPH).

- Martin

 
It's a widely accepted approximation in aeronautical engineering that level flight speed varies as the cube root of changes in thrust horsepower. Consequently, the ~8% improvement in performance that you observed suggests a ~25% improvement in Thp.

That seems like "a lot" to attribute solely to more engine power due to a 6% increase in its displacement. I suspect that you've gotten quite a performance increment as a result of improved prop efficiency, as well.

When I made similar comparisons in my own aircraft (a Bellanca Super Viking), the performance change from an old IO-520-K engine to a new IO-550-F engine -- while retaining the same propeller -- suggested a power increase from the -520 to the -550 engine of only about 12% to 15% ... still nice. There's some kind of "magic" going on with the IO-550 engine (improved intake volumetric efficiency?) that seems to yield more of a power improvement that can be explained solely by the increase in displacement.

Good job (as usual) with your in-flight documentation, and enjoy that new engine.
 
Martin Pauly said:
I cannot provide an allocation of the total performance improvements to these three contributors,
Click to expand...

Does the fuel flow not provide a good estimate of the engine power? Especially given the close control of the operating conditions - i.e. 20 degrees lean of peak.
 
Squirrelfury said:
It's a widely accepted approximation in aeronautical engineering that level flight speed varies as the cube root of changes in thrust horsepower. Consequently, the ~8% improvement in performance that you observed suggests a ~25% improvement in Thp.

That seems like "a lot" to attribute solely to more engine power due to a 6% increase in its displacement. I suspect that you've gotten quite a performance increment as a result of improved prop efficiency, as well.
Click to expand...
Indeed. People upgrading from an IO-520 to an IO-550 typically seem to report a five-to-seven knot cruise speed improvement. The prop must have played a role in my installation, and my IO-520 - while running without signs of trouble - was 2,600 hours since overhaul, not exactly in its "youthful age". I was surprised by the magnitude of improvement.

- Martin
 
Congrats on the upgrade! I imagine you are seeing a nice improvement in takeoff and climb performance as well?
 
am I looking at this wrong....on the way out your power settings were 20.3" @ 2500 but on the way back 17.2" @ 2400....
 
Spring Ford said:
Does the fuel flow not provide a good estimate of the engine power? Especially given the close control of the operating conditions - i.e. 20 degrees lean of peak.
Click to expand...
Yes - fuel flow is up approx. 1 GPH at 20 deg LOP, so that's an extra 15 HP. But that alone does not explain the speed gain.
 
edo2000 said:
Congrats on the upgrade! I imagine you are seeing a nice improvement in takeoff and climb performance as well?
Click to expand...
Oh yes - much, much better than before. I went to Colorado in June/July and effortlessly took off from Aspen at ~10K density altitude. That would not have been as pretty with the old engine and prop.
 
Remember, the HP standards for the 550 are tighter than the 520. Something like -0+5 vs +-2.5. Also, don't underestimate the power of having better baffling, as you do with those BDS ones. That really helps.

Certainly, the age of your old motor was a factor, as is the fact that the 550 is an engine that seems almost engineered from the start to run LOP.

One other thing is that I think the old thinking about HP = GPH probably doesn't directly translate. Just look at cars - you can have 400 HP engines that burn less gas than 250 HP engines. If you have a better designed engine, with less wear and better cooling, you can make more HP on the same or less gas.

I'm looking forward to seeing video of 70TB blasting out of ASE
 
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N1120A said:
One other thing is that I think the old thinking about HP = GPH probably doesn't directly translate. Just look at cars - you can have 400 HP engines that burn less gas than 250 HP engines. If you have a better designed engine, with less wear and better cooling, you can make more HP on the same or less gas.
Click to expand...

HP being related to GPH isn't always a thing, but when both are done LOP it's not a bad approximation... On the same engine.

ROP, maximum power is limited by the mass of air entering the engine. LOP, it's limited by fuel and HP is roughly 14.9 * fuel flow in GPH.

A couple things are important to note, though:

* The cylinders will not all peak simultaneously, so you may sometimes have a combination of cylinders running ROP and LOP, and each cylinder's mixture is going to be slightly different. A 6-cylinder aircraft engine is really like 6 small engines flying in close formation around a shared crankshaft. ;)

* Not all the power will make it to the prop. There are several places where power is lost.

I sure do like my IO-550 though.
 
flyingcheesehead said:
A couple things are important to note, though:

* The cylinders will not all peak simultaneously, so you may sometimes have a combination of cylinders running ROP and LOP, and each cylinder's mixture is going to be slightly different. A 6-cylinder aircraft engine is really like 6 small engines flying in close formation around a shared crankshaft. ;)
Click to expand...

If properly done, all the cylinders should run LOP. That's the entire idea of using a multiprobe engine monitor and leaning until the richest cylinder is LOP.
 
weilke said:
If properly done, all the cylinders should run LOP. That's the entire idea of using a multiprobe engine monitor and leaning until the richest cylinder is LOP.
Click to expand...

Correct. But even when you run with the richest cylinder LOP, they're still all different and you'll still have a short period during leaning with some rich and some lean. Also, flying higher with a normally aspirated plane you can get some of the power lost to altitude back by running a mixture closer to best power so you may still end up with some rich and some lean if you're running "at" peak (which is really more like "between peaks").
 
Not a Bo driver, but I would say those numbers are pretty good... you should be happy!
 
My IO-520BB V35A usually trues out at 163Kts on 12.3gph, running 22in 2300rpm and 20 degrees LOP. My brother has a ‘94 A36, and it seems to burn considerably more fuel, which wouldn’t be too bad if it had a higher useful load, but it won’t carry any more than my V tail.
 
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