How About a Ton of Payload, With Enough Horses to Make it Fly?

It's nearly ready, says Riley's President, MaryAnn Kingsley: what the C-337's basic design has teased us with all along, and never delivered, until now: a ton of hauling capability.
Riley's Super Skyrocket, with its new STC, will sport a gross weight increase on this inline twin, from the usual 4700 pounds, to 5400. This extra 700 pounds' carrying capacity translates to full tanks -- even the "big" tanks with 150 gallons -- and 1100 pounds' capacity left over, for "other," like you, your family, your anvil collection, etc.
The capacity is useful in another way, too: the Skymaster was designed to carry everything pretty much directly under the wing, so it's really tough to get the CG out of bounds, regardless how it's loaded.

Ms Kingsley told us, "The gross weight increase for the 337 Super Skyrocket is expected soon, possibly this summer. The pressure tests, the air conditioning tests -- all the engineering analysis -- is done." The Riley group is known for 'getting things done,' in the industry. (They've been one of the nation's top STC houses for years. They have a great relationship with the FAA, and understand the agency's requirements as well as anyone -- and they can deliver the data in a useful format, on schedule. Even the regulators have to love a company that does that.)
The machines sport plenty of power, too, to pull (and/or push) the Super Skyrocket along. "We got rid of the wimpy engines," Kingsley said. Now there's a pair of Continental's TSIO-520NBs: turbocharged, intercooled, 310 hp each. "In cruise, they're just loafing along," she said. "And if one for some reason has trouble -- you're still safe. It just goes straight, like it's supposed to. Now, the 337 is a truly viable people or baggage-mover, without gross weight, or CG problems."
They've gone very high-tech, as well. "We're using the same solid-model software as used at Boeing, and at Airbus," she noted.

More improvements

Kingsley said there are a lot of 337s still around, in good shape. There are two reasons for that, she says: for one, they were built like tanks; they're a solid platform. For another: "Most of them don't fly too much," MaryAnn said. "They were underpowered; and they were noisy." They have cured both those problems. The 620 hp is plenty to motivate the 5400-lb gross machine; and "We've also changed the soundproofing, and gone to a three-blade Hartzell prop. It's a really nice environment inside, now," she related.
It's too soon to know about price and delivery. Just get ready!

FMI: http://www.superskyrocket.com