I am preparing to build a Legacy and am debating what engine to use.  I think I will probably end up with a IO-550 but before accepting this as a “fait accompli” would like to explore the issue a little.

 

What I want in an engine:

 

Mission Profile:

 

-          Our Mooney Ovation is based in Baltimore and we take trips of significant length - over the past years we have been to Central America, the West Coast, British Columbia, the Caribbean, etc. 

-          We do not race or perform aerobatics.  I am looking for an engine that is reliable and economical vs. one that has the highest horsepower

-          We mostly fly at 7, 8, 9 or 10K without oxygen.  In our plane (normally aspirated) there is no speed premium for going higher.  We have built in oxygen and will go higher for good reason like strong tail winds or weather. 

-          In a plane in which there was an advantage to going higher we might do so more often.

 

IO-550 vs TSIO-550 vs. TSIO-360 / Supercharger vs Turbocharger

 

-          It is seductive to think of putting a turbo or supercharged engine into the Legacy and being able to take it into the flight levels at IVP like speeds.

-          A TSIO-550 would give us IVP like speeds at altitude.  The drawbacks are:

o        Price

o        TBO

o        Range

o        Cooling/Baffling/Cowling complexity

-          A TSIO-360 would give us less speed below 10K, but would give us more speed in the high teens and 20’s.  I don’t know how bad the CG problems would be.

-          An IO-550 is probably the safest choice

-          How difficult is it to achieve good engine cooling of a TSIO-550?  How much extra work and cost is associated with a plenum system like that of Aerochia?

-          What is the longevity of a supercharged engine?  How does this compare to a turbocharged engine?

 

Continental vs. Lycoming/New vs. Rebuilt

 

-          I have had both Continental (IO-550 G in a Mooney Ovation) and Lycoming engines (IO-360 in a Mooney 201) and have had trouble with both of them.  I don’t feel strongly about the merits of one vs. the other.

-          I have no great faith in the Continental warranty having dealt with Continental on warranty issues in the past.  (Bad lifters on an IO-550 G requiring a bottom overhaul.  No significant help from Continental).  Because of this I will probably go used rather than new.

 

Compression Ratio

 

-          I see a number of builders are opting for increased compression ratios in their engines.  What are the trade offs related to this decision?

-     Does an engine (like an IO-550) with an increased compression ratio have the same durability as one with the standard compression ratio?

–         If not, how much is the longevity affected?  How much more likely is it that I will need to replace cylinders?

 

Mags vs. Electronic Ignition

 

-          A hotly debated topic on this list and one in which there seems to be no consensus.

-          My inclination is to go with mags until the PRISM is developed (flame suit on)

ROP vs. LOP

 

-          I believe what the GAMI folks are saying and would like to operate lean of peak.  Assuming that I have a normally aspirated engine this will give me an option to stretch my range and increase my economy.

 

Miscellaneous

 

-          Some manufacturers advertise that they are “balanced”, “flow balanced”, “blue-printed”, “ported and polished”, etc.  How much difference do these things make?  Are they worth paying for?

 

Your comments, suggestions, etc are invited.

 

Disclaimer:  I am not an engineer and do not play one on TV

 

Douglas Brunner

N241DB (reserved)

douglasbrunner@earthlink.net