Performance of IO-550 versus IO-520

[Luiz Gustavo Figueiredo]

My V35B is about to overhaul its engine soon.I am thinking about upgrading to a 300-hp engine.What can i expect in True airspeed gains?I heard i might get as much as 10 knots in cruise.

[Bill Woody]

In my 1987 F33A, I saw an increase in cruise of about 5 to 10 knots, depending upon temp and DA.  However, roll, take-off and climb is where you really see the difference.  This decreases the time from point "A" to point "B" considerably more than the increase in cruise speed, because you are at altitude, much faster.  

[Bryan Wood]

You can calculate the speed increase pretty easily.  

300hp/285hp = 1.053% gain in horsepower.  Take the cube root of 1.053 which gives you 1.01736343290425.  (Here is a cube root calulator if you want to play around with this. http://www.csgnetwork.com/cuberootcubecalc.html )  Anyway, you need to multiply 1.01736343290425 with your cruise speed to get the new speed that you can expect from going with the bigger engine.  

To give an example of the increase assuming a 170 knot cruise with 285 hp you will increase your speed up to 173 knots with an IO-550.  This will probably be unpopular with some, but it should be very close to what you will get.  The climb and takeoff roll however as stated earlier will improve.  

[Arlen Stauffer]

Luiz,

It's true that just adding a few horspower doesn't give a tremendous increase in cruise speed.  And, more horsepower means more weight and a higher fuel burn.  The 756 NM trip from Daytona Beach to Toledo would take 4 hours and 26 minutes at 170 knots, and adding 10 knots to the speed would save you just 14 minutes -- not much difference....

There are, of course, ways to squeeze every additional knot out of it (if that's your goal):

- more horsepower

- mods that reduce drag

- re-rigging if that's a bit off

- tuned exhaust (as in the Atlantic Aero STC'd IO-550-R)

- composite (lighter) scimitar prop

- wax

Best wishes,

[Don Lawton]

I understood that one of the advantages of the IO-550 over the IO-520 was the 550 would operate LOP much smoother than the 520.

[John Collins]

 

You can calculate the speed increase pretty easily.  

300hp/285hp = 1.053% gain in horsepower.  Take the cube root of 1.053 which gives you 1.01736343290425.  (Here is a cube root calculator if you want to play around with this. http://www.csgnetwork.com/cuberootcubecalc.html )  Anyway, you need to multiply 1.01736343290425 with your cruise speed to get the new speed that you can expect from going with the bigger engine.  

To give an example of the increase assuming a 170 knot cruise with 285 hp you will increase your speed up to 173 knots with an IO-550.  This will probably be unpopular with some, but it should be very close to what you will get.  The climb and takeoff roll however as stated earlier will improve.  

My understanding is that the relationship between additional power and resultant speed increase is not quite as bad as the cube root, and that typical improvements going from an IO520 to an IO550 are between 5 and 10 knots.  Also note that the IO550 is specified as 300 HP -0 to +5%, whereas the IO520 is 285 HP +/- 2.5%. So a best case power improvement could be from 278 HP on the low end of an IO520 to 315 HP on the IO550, or a net increase in HP of 37 HP.

[John Collins]

 

Luiz,

It's true that just adding a few horsepower doesn't give a tremendous increase in cruise speed.  And, more horsepower means more weight and a higher fuel burn.  

The IO550B weighs the same as the IO520BB.  Higher fuel burn is an option on the IO550 and my understanding is that the specific fuel consumption is marginally better for the IO550 than the IO520.

[Bryan Wood]

 

 

Luiz,

It's true that just adding a few horsepower doesn't give a tremendous increase in cruise speed.  And, more horsepower means more weight and a higher fuel burn.  

The IO550B weighs the same as the IO520BB.  Higher fuel burn is an option on the IO550 and my understanding is that the specific fuel consumption is marginally better for the IO550 than the IO520.

I think there are several factors to consider.  A pure horsepower gain can be calculated and predicted.  Gains from replacing the prop, baffling, etc. could account for additional gains that would make the finished product look more dramatic than an engine upgrade alone could provide.  I didn't think about that when posting previously.  

Once a plane is finished with the conversion however the cube root rule could be proven to be valid for the airframe by flying a couple of power settings and noting the speeds for each.  Then do the calculations and it should prove out that the Bonanza airframe does not escape the rules that other airframes are restricted by, but rather it benefited from several changes all implemented at the same time.

[Mike Thompson]

John;  

Don't forget when comparing the 520 / 550 HP differences the difference between rating systems.  The 520 was rated the old way, with life support only (fuel pump and mags).  The 550 is rated at the 300 +5/-0% with air pump and alternator also.  Potentially 50 HP difference...

[Drew McWilliams]

I am very impressed with the IO-550 upgrade in my V35B, But I can't express enough you need to install the new D'Shannon Baffling Kit for proper cooling. The IO-550 seems to be more heat sensitive than the IO-520. Also the fuel flow on takeoff, needs to be at the top of the scale, or a little above for cooling, especially in hot weather.

Drew McWilliams

N1040W

 

[David Niles]

I have a Baron, so two engines and am getting closer to TBO.  Has anyone out there done the conversion to the IO-550 on a Baron and if so what type of increase in climb rates are you seeing?  I am less concerned about cruise since I am doing great with that today and five knots on 200 knots is not much of a factor.

[Luiz Gustavo Figueiredo]

Drew, what do you mean by "very impressed"?  Could you give me some performance and temperature numbers before and after the switch?

[Bill Woody]

While using the above calculations for the increase in power, bear in mind you are comparing engines with the same compression, efficiency etc.  The reality is that when you remove your tired 520, and replace it with a new 550, as I did, the difference will be considerable.  Those calculations result in the difference when you install a fresh 520 vs a fresh 550.

[Robert Martin]

This is more or less an engineering question. The new velocity with the increased HP(IO-550 vs the IO-520) can be calculated by taking the cube root of the quotient of the new HP divided by the old HP then multiplying by the old airspeed. Variables can come into play here that can make the calculation inaccurate. You must know the exact HP of the new and old engine which is difficult to determine. The IO-520 was certified under the old CAR's which specified plus or minus two and one half percent for full power. The IO-550 was certified under the new FAR's which specified minus zero to plus five percent for full power. Now assuming 300 HP  for the IO-550 minus 3 HP for alternator and pump and 285 HP for the IO-520 minus 3 HP and calculating the new airspeed with an old airspeed of 170 you come up with a new airspeed of 173. Now suppose the new engine had 300 HP plus five percent and the old engine had 285 HP minus two and one half percent you would come up with 177.3 knots. In conclusion the incease in air speed can vary between 3 to 7.3 knots. Since HP will vary from engine to engine it is hard to say what the increase in airspeed you will get. I am installing a new platnium IO-550 with BDS baffles and a new simitar prop in my F33A. I will report some exact figures after flight test.

[John McGuire]

The 550 does burn more fuel than the 520 but remember it will go faster so the MPG (miles per gallon) is exactly the same and you get there a little sooner.  John McGuire