Boy, some of these guys sure like to jack up the price of someone else's project!! Sure the 4 stroke twin is really neat but look up the price! This is going to be this guy's second airplane not his ultimate dream plane of all time. I have the same GP Cub ARF with a sideways mounted OS 46 FX w/pitts muffler and it is NOT underpowered. His TT46 pro is equal to my OS 46 FX so it would be fine setup for his first scale plane and at an affordable price. As previously stated the pitts muffler will improve the exhaust note to an almost 4 stroke sound without breaking the bank. If funds are not an issue then of course a 4 stroke is nice but not mandatory. I also have a similar sized Thunder Tiger J-3 Cub (these are 1/5th scale cubs) also powered by an OS 46 FX W/a pitts muffler. Again, just fine in the power department for scale like flying, will do loops and rolls, and no problum taking off from a grass runway. They don't all have to have 4 strokes to be enjoyed. My biggest Cub is an early Hanger 9 fabric covered 1/4 scale J-3 with a Saito 120 4 stroke. For me, that's my ultimate Cub, but I also enjoy flying my other 2 stroke powered Cubs. Nothing wrong with them at a much lower investment cost. "89", if you have purchased the TT 75 4 stroke, it will fly your Cub well, but the 46 2 stroke also would have done the job, it's just a matter how much you want to spend on each new project as you add to your hanger. BTY the Great Planes J-3 is a sweet flyer, you will enjoy it no matter your engine choice.