For sport stunting, the Black Widow is just fine. Not enough tank capacity to do the whole pattern. The model should have between 120 and 170 sq.in. area.

Among the other Cox engines, the Medallion has good power (way more than the Black Widow) and very steady running with good fuel draw. The model should have from 150 to 200 sq.in. wing.

If still more power is needed, the Tee Dee is the thing, but I strongly recommend running pressure from that side nipple. This engine will power models from170 to 235 sq.in nicely.

That said, the NV Big Mig is an excellent choice, equivalent to the Medallion, and actually available new!

If you can give us some idea of what model you plan to fly, we can make a firmer recommendation.

Check out rsmdistribution.com for some kit ideas.

No ones mentioned the Brodak engine, anybody using it?

My first choice it the WingMaster like Duke has posted in another thread. Second choice is Walt Musciano's Wizard.

I'll run an external tank to fly the entire pattern. After I get used to flying CL again, I'll be building a Smoothie. 

Those NV engines are interesting! There's two versions but the NV 049 Aero CL seems to be the right one for stunt flying.

I'm not necessarily set on Cox engines, they're just about the only thing around when I started, back in the 60's. EX engines has their "Black Lynx" engine that looks like a good one been then why would you spend that much for an engine with plastic parts?

I have what I think is a related question: If you are flying a more powerful engine, can you use longer lines? That would be a plus in my mind.

Yes, more power allows longer lines. Antone Kephart flies a baby Magician with a pressure fed, drilled out venturi AP Wasp .061 on 50' lines. 5 second laps and all the room in the world to maneuver. The model is a short kit that is on Eric Rule's "secret menu". Basically the essential laser cut parts for the model as presented in Flying Models many moons ago.

I was thinking you wanted a Cox engine from your initial post and the Ex model Engines Lynx is a good choice for a reedie. People start talking about TDs and Medallions. well you can't usually buy a new one of these from Cox Int Or Ex Model Engines. Just about all Cox reedies have plastic parts so no reason to dis it!
You can buy a Norvel 0.049 or 0.061Big Mig for around $80, they are easy to use and have plenty of power for 50 feet lines and you can have a decent stunt plane. Jim Thomerson's Cheap Thrill is a great design amongst many others.

Best of luck,

Andrew.

No disrespect for plastic parts. Just concerned about how well they hold up under figure 9s and precision single point landings 

No problem. The above looks good to me.

Those are two fine engines. They'll crank right up for you every time. The Black Lynx is the hottest one of that type Matt at Ex Models makes. And Bernie's Cox Int'l Killer Bee II is right up there too. Get some extra head shims, because the head, especially the one on the Lynx, has extremely high compression and you'll need to experiment to find out how many to use depending on your fuel, elevation, and temperature. Using Sig Champion 25%, I've used as many as five shims in the heat of the summer, and down to three in the dead cold of winter(I'm at 300' above sea level). Or with the Killer bee (Cox high comp. head), two or three is usually the answer. If you try different nitromethane percentages, a general rule of thumb is to add a shim for every extra 10% nitro. I feel you will get the best service with about 25% nitro. 35% isn't worth the added stress on it for the small gain in power.

These SPI engines really wake up at the higher RPMs that you'll get with a prop smaller than 6". I like to buy the Master Airscrew GF series 6x3 props and cut them to 5.5" or less. 5" is as small as you'll want to run on it, and will give you the highest RPMs. A lot of people like the Cox black props, commonly called rubber duckies, because they are very flexible and durable in crashes. I find them to be harder to balance than the MA props though. Balance is important at high revs and will prolong the bearing life.

One last thing to add is, with the large venturi on the Lynx and Killer Bee, your tank position is critical and really affects ease of cranking. The shortest fuel line possible is best, and keep the tank about level with the venturi height. Too low won't draw fuel as well and too high will flood the engine easily. I feel the mylar reeds are the best replacement part. Reeds will become mis-shapen after a while. And after initial break-in and a couple of quarts of fuel, keep an eye on the piston rod play. The ball socket can loosen and may need to be reset. After the first time, it won't happen so often.

Good luck, and let us know how it runs.

Rusty