The trick to intelligent overpowering is to add useful weight and power to the airplane. I see many cases here of RCU of people adding a huge engine to a plane and maybe only adding speed or climb, but losing agility, which is something I look for in most airplanes.

First, you need to match the power to the type plane. Next, you need to insure you just don't add more power, but in addition, add more weight that nearly negates your power.

In a fun fly plane you want extra power to pull up from a fall out of a hover or some maneuver near the ground. You also don't want to limit your plane by also adding useless weight. As an example, a Goldberg Extreme 330 usualy builds tail heavy with a .46. The mean weight for a .46 is about 17 ounces (16.5-17.7 from my engines). If I need 3-4 ounces nose weight, I can add an engine that weighs that much more without changing anything. It turns out the Saito .91 weighs 20.5 ounces, only 3-3.5 ounces more than a typical .46! You need to trim the nose a little, but the big Saito .91 can be shoehorned in, giving you tons of extra power without requiring any tail weight to compensate. No other 4-stroke .91 can do this.

The Burrito, on the other hand, has its moments chosen for a .46 and would be nose heavy with anything larger. It is also lighter and flys very well with the smaller 2-stroke.

My buddy and I have a scale Northrop A-17A 30's era dive bomber. It was the predesessor of the SBD Dauntless. (At the time Northrop was a division of Douglas.) It is a radial engine plane with, naturally, a short nose. Ours was built by my friend for me and was scaled up from smaller plans to a 68 inch span. During construction, we found that a normal .61 would require several ounces nose weight to compensate. It just happened that I had a Magnum 1.08 in a Joss Stick that I used for testing and running in .91-1.20 size engines. We checked it and the plane required no additional lead. Further, the prop the big Mag could turn, a 15-8, would easily clear the radial cowl. It has been a great flying scale plane, very aerobatic (it flat spins) and the extra weight and power hasn't hurt at all.

As for using a .61 in a .46 size plane, this is the worst engine change there is, in my opinion. Most .61 2-strokes weigh over 25 ounces compared to the 17 ounce .46, by my weights. That is just over a half pound added. A .50-.53 with a Tower muffler or tuned muffler like the Ultra Thrust will more than likely give you more total performance.

Furthermore, in my opinion, the .61 is heading the way of the .40-a useless engine that has very little future. Why buy a .61 when there are .75s and .91s in the same case, weighing the same, but producing much more power. Ball bearing .40s hung on for a while, but do you see many now? Why buy one when for $10 more you can get a .46 with more power and the same weight. I think the .61 is headed that way.

I just noticed that Tiger Shark is listing (but not in stock) a .56 in the .40-size case. It's a punched out .52. 16-17 ounces of .61 killer. How long before other manufacturers catch on. And if you don't think the .40s are going, notice the Irvine .39 and the Tiger Shark .39. Basically the same displacement as a .40, but built in a .32 case at 12 ounces. With these engines, we are talking power-to-weight ratio in a fun fly plane. Now go power your .28-.32 size plane with a .39 and your .46 plane with a .56. Now you are talking serious overpower without a weight penalty.