ULTRAcooling the Cessna 340 and 414

Reprint from Charlie Papa Tango Magazine

In my experience, there are at least two things pilots can’t get enough of. One is more power and the other more fuel. Certainly, if you asked pilots for a list of improvements they wanted, it would include more speed, more useful load, greater range, shorter takeoff distance and safer single engine operation. In most cases, these improvements relate back to having more power and more fuel. For example, with more power, you could safely carry more weight and also improve the takeoff and single engine performance. If you had more fuel, you would have more range at the same speed or more speed at the same range, but you may also need more power to carry the extra weight of fuel safely.

I could certainly be described as an advocate of both more power and more fuel, but like you, I am also concerned with efficiency and cost. Before I became involved with the 340 or the 414 Cessna airplanes, I had the pleasure of flying some aircraft that were upgraded with higher output engines. Most notably, an S model Bonanza that was upgraded from a naturally aspirated 285 HP engine to a turbocharged intercooled 350 HP Lycoming as used in the Chieftain. Another was the Aerostar, which jumped from 290 HP to 350 HP with Chieftain engines and was turbo-intercooled in the process. Both the Bonanza and the Aerostar demonstrated impressive climb and cruise improvements and both were much safer and easier aircraft to fly. In addition, they were both more fuel efficient. The Bonanza and the Aerostar engine change programs were accomplished by my company, Machen, Inc., a sister company to American Aviation, Inc.

When we upgraded the Bonanza and the Aerostar we learned a great deal about the importance of proper intercooling. Without it, we lost 90 horsepower at altitude. By optimizing the intercooling systems on those aircraft, we restored the lost power and picked up 10 to 15 knots more speed while reducing fuel consumption and cylinder head temperatures. The engines seemed to run more smoothly and they were noticeably more powerful and fuel efficient.

After completion of these two engine change projects, it was logical, from a business standpoint, to apply the single most powerful and beneficial part of the engine installation, the intercooling portion, to various other aircraft in the general aviation fleet. This is because intercooling is the biggest improvement in performance for the least amount of money. We concentrated on the business twins and completed installations on the Beech Duke, Piper Navajo, Cessna 337P and Cessna 303.


During this time, one of our previous customers, Mr. David Smith acquired a Cessna 340 and called me regarding any improvements we could offer for this aircraft. He brought the 340 to our facility for evaluation and after a visual inspection, we suspected there might be room for improvement in the intercooling system. Thus began our involvement with the powerplant in the Cessna 340 and 414 airframes.

After instrumenting his 1978 Cessna 340, we test flew the aircraft to determine the temperature and pressure of the air in the following locations: 1. entering the turbocharger inlet, 2. exiting the turbocharger and entering the intercooler, and 3. exiting the intercooler and entering the engine. As expected, the existing intercooler was very poor due to low ram recovery, excessive pressure drops and improper heat exchanger design. Because the temperature of air in the #3 location (entering the engine), continued to rise as the aircraft climbed to altitude, both the climb and cruise performance and the engine efficiency deteriorated. This is because at the same manifold pressure and RPM, an engine that is injesting hotter and hotter air, loses power rapidly and requires extra fuel for cooling and detonation protection. When we later tested a RAM modified series III, 325 HP conversion, the temperatures were even hotter. That was not unexpected, as the modified engine uses even more manifold pressure resulting in more heat of compression in the induction air and with RAM conversions, the original intercooler is simply reused as in the standard airplane. The actual power loss we calculated at either climb or cruise climb power was about 40 HP. The cruise performance suffered equally as much as the climb, again due to superheated air entering the engine. The power loss in cruise resulted in a penalty of 7 to 12 knots depending on the altitude and power setting.

Knowing pilots wouldn’t be happy if they knew they were giving up 40 HP in climb and 7 to 12 knots in cruise, we assumed there would be a good market for correcting the problem with a properly designed turbo-intercooling system. By restoring the lost power, we could in effect give them a power increase. The increased power would result in a fuel saving as they would be at rich climb fuel flows for less time. Properly intercooled engines are also more fuel efficient in cruise and more forgiving of lean mixtures which would extend engine life. Believing we could satisfy the pilots desire for more power and save some fuel in the process, we set about designing a proper system. Our experience with other aircraft allowed us to complete the task in a little under a year and FAA certification was completed shortly thereafter.

In addition to better climb and cruise performance, our takeoff distance on a hotter than standard day was shorter, our single engine climb and ceiling were higher, and we were now able to maintain high cruise power settings at low RPM for greater fuel efficiency, engine life and noise reduction.


We had Mr. Smith’s turbo-intercooled 340 and a RAM Series II 340 here at the same time at one point and we made a climb performance comparison on one of our test flights. With the pilot of the American Aviation turbo-intercooling 310 HP 340 holding 31.5″ and 2450 RPM, I flew on his wing in the RAM 325 HP 340 holding 34″ and 2500 RPM. It took my RAM converted 340 an extra 2 1/2″ MAP and more RPM to stay in formation. As we climbed up through 10,000 ft., I could no longer keep up, even though I was pulling more manifold pressure and RPM. The reason is really simple, it was about 20°F hotter than a standard day, and at 10,000 ft. the American Aviation turbo-intercooled 340 was breathing compressed air that was considerably cooler than the RAM modified aircraft. The 310 HP 340 climbed better because it had more power! By that I mean it had more power than was actually being produced by the RAM airplane’s engines which was breathing superheated air due to the inefficient stock intercooling system. After turbo-intercooling the RAM 340, its cruise-climb performance increased about 300 ft. per minute at 10,000 ft. as one would expect. It’s interesting to note that at 38″ and below, a RAM modified engine is virtually identical to a standard engine, and the stock intercooling system remains unchanged. Therefore, the RAM engine responds as well to our intercooling system as the standard engine. The extra power offered by RAM is accomplished by boosting the manifold pressure above 38″. At these higher manifold pressures, the temperature of the induction air elevates quite rapidly and is in greater need of our system.

You might assume that intercooling and engine that is already intercooled would be a risky business decision due to the difficulty in convincing customers of the need. We were also concerned but confident in the increased performance and the fact that we were giving them “more power”. Fortunately, the performance increases have spoken for themselves and many of our 340 customers have written testimonial letters extolling the virtues of the system.

To help differentiate our system from the standard intercooler, we have given the high efficiency system the name ULTRAcooling. We have produced a video tape to explain some of the advantages of the ULTRAcooling system and also to familiarize Cessna 340 and 414 owners with our company. In the video tape, there are shots of the instrument panel showing the power settings, fuel flows and speeds you can expect once ULTRAcooled. We are making this tape available to all 340 and 414 owners on a complimentary basis. With nearly 200 aircraft already updated, our sales to date have exceeded the original projections. Hopefully as more owner become aware of the performance advantages the ULTRAcooling system offers, we will update the vast majority of the fleet. ULTRAcooling is certainly the most performance for the money and the most efficient application of “more power”.

Jim Christy