After studying the "List Your Setup", and reading as much as I can find I am still a little lost. I would like to convert my Ring Master Imperial to electric. It flew well with an Enya .35 and probably a 10 x 6 prop 40 or so years ago. I have never done any competition flying or ever plan to, I just make squiggles in the sky some may call loops and eights.
This was my biggest plane ever at 52 in span and 680 sq in wing. As it sits now, it weighs 29 oz. (no motor or tank)
Doing the calculations on it's weight I come up with what seems to be a reasonable power solution however when looking at similar sized planes in the List Your Setup they all seem to be heavier and a lot of that seems like the power plant and batteries.
So, if I may, I would like some suggestions for a power plant, motor, battery, speed controller and prop.
3 to maybe 4 min tops on flight duration. The plan includes stripping all the old silk span covering, making the necessary repairs from its last not so smooth landing and removing as much oil as possible. Maybe even dropping an oz or 2 in the process.
Any and all suggestions would be appreciated as I want to get this right as it is not one of my disposable foamies.

How much beyond a 1:1 thrust to weight ratio is recommended for good flight characteristics in loops, 8's and squiggles.
Which is more important a good power to weight (watts/lb) ratio or thrust to weight?
Is there a point of limited returns for either?

Right, Dennis, this may be a porker but he says that it is 29 oz with no power package.

If the conversion is going to happen, the first thing do is to remove entirely the old motor mounts. The motor will be a firewall type mount and this should save some weight. You need to decide whether to front or rear mount the motor as this will determine how the nose is to be configured. Also, with the short coupled tail you may need to have the battery buried into the wing area (at least partially) to get a reasonable CG. That may require some re-engineering of the fuselage/wing area.

Good luck and let us know how it is progressing.

You may not want to hear this, but the prudence of trying to convert a 40-year-old oil soaked model to electric may be questionable. Safety should always be a paramount concern and there is a good chance you won't be flying safe with this model. How do you propose to clean it well enough to get a solid epoxy joint for the new motor mounts, for example? How to be sure the control system is sound and not going to rip out of the wing?

Sorry to be a wet blanket but we see this kind of vintage stuff at our field sometimes and I cringe at what could happen, and what does happen. Depending on how you value your time, it may be cheaper to start with a modern ARF that is an easy  electric conversion, or get a Brodak or RSM kit that is designed for electric use. You would be in the air sooner and with more chance of success and definitely with a better margin of safety.

Generally, conversions weigh more than a purpose built new bird, but I think you should be OK.  Stripping it down and using a 'cote finish should save a little.  While its exposed recheck the glue joints and look for any opportunities to remove anything that's heavy.  As I recall the Imperial does not have any plywood doublers so use care in reoming the beams.  Heck some folks have cut the nose off completely and grafted a new one on.  Detail changes can help too - for example, if it has old style wheels you can save an ounce or more just switching to new style foamies.

I would endorse the power system that 55Chevr listed.  The Turnigy 3530 is about 1/2 the size motor he listed, the equivalent Turnigy is a 3542.  Match that to a 11x.5 pusher and a 4S pack and you will be one happy camper.

The 2200  packs will limit you to about a 4-4:30 flight time, but in your first post thats all you said you wanted...

Amperial - good one!

I really can't say much about motor wattage - you never know how this were determined, any motor can show a high wattage capaility - for 1 or 2 seconds!  I think it is the statistical analogy to using HP numbers for IC engines - ie, of uncertain value.

I try to start with the prop and work back  The R.I. was designed for a 35 size engine, most likely turning a 10" prop - and struggling a bit to get the job done.  Today that airplane would be powered for an 11" prop.  So that is the baseline for the electric.

I had a 3530 in a 50 oz airplane turning a 10" prop.  It lasted til the 4-leaf clover, after the first loop there was a screech and that was that.  Cutting to the chase, the 3530 is good for up to a 9" prop, the 3536 for 10", and the 3542 works great with 11".  Get one with a kv in the 900-1000 range, put it on 4S and go commit aviation!

BTW, Turnigy uses exterior dimensions, if you were to cross ref to Arrowind, AXI, Cobra, etc, their szies would be 2810, 2815 & 2820 (give or take a litlle)

The R.I.'s were famous for coming out heavy - yours actually sounds lighter than most!  If you can do the strip/refurb without getting heavier I think you will be OK.  I suggest that you try to notch out the LE about 1" deep to provide a little more room for the Lipo...

How does the Sterling Super Ringmaster perform?  And how about the Brodak S1 Ringmaster kit?

Ok, the dim bulb in the brain has illuminated just a tad more. I believe my impression of physical size of a motor and those dimensions sort of placing it into a class of motor is true. Closer inspection of a manufacturers choice of either using the inner or outer dimensionality to name/class their motors will be essential to keep my brain from hurting so much for future and other present projects.

Dennis, glad you liked the "Amperial" and ever so glad you passed along the dimensional details you have saved my Turnigy 3530 and possibly the plane from an early demise.

The Exceed Rocket 3020-860 is added to the short list of necessities.

Many thanks to all and I'm certain there will be more questions to come.

A significant advantage to electric power is that a plane doesn't have to be fuel proof.  I flew electric RC planes with latex house paint on them.