Atlantic Aero's 550 Conversions

210s, 206s and Bonanzas

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The Continental IO-550P engine with what are called "cross-flow" heads is the latest in piston engine technology. Versions of the engine are used in new Cirrus and Columbia airplanes where they have become legendary for their power output. Now Atlantic Aero in Greensboro, North Carolina, is offering what they call 550 Tuned Induction Conversions for the 1970 through 1984 Cessna 210s K through N, for Cessna 206s, and for Bonanza S35s and later, plus Bonanza 36s. Later model Bonanzas have IO-550 engines but not with the cross-flow heads.

The conversion, which does not include turbocharging, has become a popular option for owners of turbocharged 210s. In fact, most of the conversions are being done to T210s, moving the airplanes from a turbocharged powerplant to a normally aspirated engine with more power.

The first thing that anyone asks is how this converted airplane compares with new airplanes. On speed, the converted 210 would be about the same as a Cirrus or Columbia on the same fuel flow. On price, if you were to purchase a good used 210, gussy up the avionics and cosmetics a bit, and put the new engine in, the investment would be in the $250,000-300,000 range. There would be no glass cockpit and the airplane aft of the firewall would still be more than 22 years old, but it would have a big six-place cabin and enough useful load to carry four people and baggage on trips of reasonable length.

If a person already owns a T210, the price of the conversion is $74,299 installed at Atlantic Aero. This includes virtually everything up front, including a new scimitar prop from Hartzell. A new engine mounting system is also included that adds two mounts and makes this one of the smoothest piston airplanes ever. A complete kit for a field conversion and de-turbo of a T210 runs $64,213. Most of the conversions are done in the field.

The IO-550P has slightly better specific fuel consumption than does the normal or turbocharged 520 engine that it replaces. When compared with the normally aspirated 520, it does better on power with altitude and will actually cruise the same speed at 12,000 feet that the 520-powered airplane does at just under 5,000 feet, all while burning substantially less fuel. Looking at it another way, the 550 airplane can fly as much as 12 knots faster than one with the 520 while burning a bit more fuel. Go fast, save gas-it's your choice.

This engine is rated at 310 horsepower with a margin of plus 5 percent and minus 0 percent. By comparison, the 520 engines were plus or minus 2-1/2 percent. That means the IO-550P might make over 325 horsepower. If it does, that means it will burn more fuel.

Additionally, the 550 has a TBO of 2,000 hours compared with 1,700 for the 520. The result of all this is that the difference in price between replacing the 520 and upgrading to the 550 can disappear because of operational efficiencies.

I flew a 1978 210 that has had the conversion for about 700 flying hours and that was refurbished inside and out at the time the engine was done. It was like flying a relatively new airplane.

With the cowling off, the installation looks clean and simple, especially when compared with a turbo or pressurized 210. On this installation, no major cowling changes are required even though the induction system is on the top of the engine. The Bonanza conversions require a new top and nose cowling as well as a prop extension. A new exhaust system is part of the package for de-turbo installations as is a new air induction system.

On takeoff I expected better acceleration than in my P210 but it wasn't there. That is logical because my engine also develops 310 horsepower for takeoff, though that output is limited to five minutes, while there is no limit on the IO-550P.

The throttle can be left all the way in for climb, which seemed to average 1,000 feet per minute at 110 knots in rather disturbed air. At 6,500 feet I selected 2500 rpm, which was the smoothest in this installation, left the throttle full forward, leaned to 50 rich of peak and found a true airspeed of about 180 knots on just over 17 gallons per hour. The maximum structural cruising speed of a 210 is 167 knots indicated and this could be a limiting factor at low altitude or in cold air.

This engine runs well when operated on the lean side of peak EGT and, in fact, you can lean the mixture until it is far past 50 lean, and the engine still runs smoothly until it starts to wind down because of the excessively lean mixture. Low rpm operation isn't as smooth as 2500. This is a common characteristic of 210s and I thought the new engine mount system would result in smooth running at low rpm, but it still has a low-order vibration when the rpm is dialed back. The airplane has Bose headsets so it is nice and quiet as well as smooth.

The 210 does well with this engine but the airplane that should really get up and go is the V-tail Bonanza. It is lighter and there is a bit less drag, so it should get very close to 190 knots at cruise, or up near Baron speeds. Even though it requires those cowling modifications to accommodate the top-mounted induction, the Bonanza mod costs about the same as one for a T210.

If there is a typical customer for this mod he is an older pilot who has an airplane, wants to keep it, but also wants to build himself one last airplane. The engine would bring that part up to the minute, and paint and interior would take care of the looks. Then there is the instrument panel. Pilots do love to spend money on avionics and autopilots and the 210 panel will accommodate most anything a person can afford. Many 210s are flying with ice protection systems and airborne weather radar, too, so the airplane can be as complete as an owner wants. There are some nice choices here, just waiting to be made.