The Riley Super 340 is a conversion from a stan¬dard Cessna 340. The 285 hp engines in a standard Cessna 340 and the 310 hp en¬gines in the Cessna 414 are basically the same. Some additions and changes in the area of the induction air intercooler, oil cooler and intake manifold elbows make it possible to extract more power from the 414 engine, through the use of three inches more manifold pressure. Fuel injection, cyl¬inder baffles and other modifications are also necessary. Riley does all this to the en¬gines in a 340 to convert it to a “Super.” When Riley finishes, the engine is just like the 310 hp engines built by Continental and installed in the 414 by Cessna. Even the data plate on the engine is changed to reflect the change. The airplane then be¬comes a 340 with the 414 powerplants. Weight increase is minimum, at 22 pounds.
Additional horsepower helps rate of climb more than anything else, and in the Super 340 conversion, there’s a bonus over and above the apparent simple increase in horsepower. The 285 engines have a mani-fold pressure restriction starting at 16,000 feet; the 310 hp engines are unrestricted to 20,000 feet and can pull 285 hp to 22,000 feet, for a 6,000 foot advantage over the straight 285 engine.
There is one qualification to the Riley Super 340 package. Even after conversion, the engines are “flat rated” at 285 hp, meaning that you aren’t supposed to use the full 310, even though it is there and the engine is built for it. This is because Riley would have to do time consuming certifica¬tion work, such as developing figures for a higher engine out minimum control speed to reflect the higher horsepower. It will come in time; in the interim, Super 340 pi¬lots are told to mind the 33 inch (which means 285 hp) redline on the manifold pressure on takeoff. That’s no problem, but I’d imagine that in an engine out situation, it would be tempting to go for the extra three inches for extra single engine rate of climb, even acknowledging that Vmc would be a little higher. When climbing and cruising, you can get full benefit from the conversion by using 75 percent of the 310 hp for cruise climb. Again, the benefit is most no-ticeable at altitude: The 285 engine is good for 75 percent climb or cruise power to 20,000 feet; converted, it will deliver 75 percent of 310 hp to about 25,000 feet and 75 percent of 285 to about 27,000 feet. So you can see that the Super 340 really pays powerful dividends up high.
Riley Super 340 / Cessna 340
Engines: 2 x Continental TSIO-520-J, 310 hp
Seats: 6
Wing loading: 32.47 lb/sq.ft
Pwr loading: 9.63 lb/hp
Max TO wt: 5975 lb
Empty wt: 3745 lb
Equipped useful load: 2131 lb
Payload max fuel: 715 lb
Range max fuel/ 75% cruise: 1420 nm/6 hr
Range max fuel / 55% cruise: 1732 nm/ 8.5 hr
Service ceiling: 32,000 ft
75% cruise: 235 kt
55% cruise: 205 kt
Vmc: 86 kt
Stall: 71-79 kt
1.3 Vso: 92 kt
ROC: 1800 fpm
SE ROC: 350 fpm @ 100 kt
SE ceiling: 16,000 ft
Min field length: 2130 ft
Cabin press: 4.2 psi
Fuel cap: 840/1416 lb
Riley Super 340-8 / Cessna 340
Engines: 2 x Lycoming IO-720-B1B, 400 hp
Seats: 6
Wing loading: 32.47 lb/sq.ft
Pwr loading: 9.63 lb/hp
Max TO wt: 6600 lb
Empty wt: 4525 lb
Equipped useful load: 1976 lb
Payload max fuel: 560 lb
Range max fuel/ 75% cruise: 1238 nm/4.4 hr
Range max fuel / 55% cruise: 1716 nm/ 7.2 hr
Service ceiling: 45,000 ft
75% cruise: 276 kt
55% cruise: 240 kt
ROC: 2500 fpm
SE ROC: 600 fpm
SE ceiling: 30,000 ft
Min field length: 1600 ft
Cabin press: 4.2 psi
Fuel cap: 840/1416 lb
