I decided to fly Imac this year for the first time . iahve been flying for some years now off and on but would like a challenge and not just burn fuel

the two planes i am building right now is a greatplanes matt chapman cap580 and a greatplanes Yak 25% . the yak will have a DA50 .the cap580 i am between a YS63s or a OS61dx .

Question ... which engine will be better for the cap ..?..i use 15% coolpower for my planes and 305 for heli.....i fi go with the YS do i have to use 20% . Also in the 20 years i have been in this hobby i have never owned a 4 stroke engine .

Question which plane would be better to use at the imac meets .....?

thanks

Use the Yak for IMAC. Bigger flies better and it is easier to control. Use the CAP580 for practice. Don't practice with the CAP just before a contest. Welcome to our nightmare. I would suggest the 20% for the 4 strokes. The YS does require a different tank set up. It is pressurized and some tanks will burst under the pressure. For simplicity use the OS.
EXCAP232

I agree on the Yak for competition and the 580 for practice. When I say 'practice' I mean foolin' around or learning a new maneuver where you don't want to risk your big ride. But if you know the maneuvers in your schedule, then I would fly the Yak extensively, maybe even exclusively, get it trimmed to your complete satisfaction, so flying it becomes second nature. Check the IMAC website for the Peter Goldsmith trimming procedure.

I own about a dozen YS engines, have set them up with pretty much every brand of tank in general use, including a few cheap ARF tanks, and never had one split on me. I have heard of such things, but never seen it. Don't be afraid of the YS, it's a super sweet performer, but absolutely 20/20 fuel to get decent performance from it, on up to 30% nitro after you fall in love with it. The YS loves an inverted mount. Get yourself a Venus (the original, not the II) or a similar 40 size pattern model, put the YS in that, and you'll have a very capable small model to practice your IMAC routines with. My Venus with YS53 and YS63 provoked more spectator comments & questions than anything I've ever flown.

what would be the advantages of going with the ys63.............

I don't know the CAP580, but I imagine it wants a side-mounted engine, which would argue in favor of the two-stroke. The YS can be side-mounted, but I think it's better suited to an inverted mount, as you would have with the Venus or other pattern type model. YS63 would be good power for a five-pound up to a six-pound total weight model.

If you've been flying 20 years and are new to four-strokes, the YS is a great way to broaden your experience. The YS is supercharged, which means it gulps in more air than a non-supercharged four-stroke. The more air to burn is the reason for the high nitro requirement. The pumped & regulated fuel system is different from what you're used to with the two-strokes, but I don't think it's significantly more complicated, given that you have the freedom to put your fuel tank on the CG, and don't have to worry about whether it's higher or lower than the carb spraybar. The regulator solves the fuel siphoning problem, and pretty much avoids any flooding of the cylinder. Starts are very easy, but usually do require an electric starter. Also, with the inverted mount, you'll probably want a remote glow hookup for convenience and safety, so you don't have to reach under and behind a spinning prop to remove your glow lighter.