I need some help on choosing an engine for a seagull ultimate 90. I have a OS120 surpass but I dont know if it will suffice. I would like to put it on gas but I dont want it to fly like a brick either. If I go gas I will use a crrc26. If I go glow I would like a 4s but may opt for a 2s. Please give me some imput. Prefer real life experience. I would like it to have good vertical climb. I dont do extream 3d but would like to learn.

ANYONE???</p>

How much does the plane weight rtf?

the advertised is 10-11 so im guessing 12 to be safe</p>

I would say neither motor has enough to fly it with much/any extra power left at 12 pounds,especially a bipe. Try to hit the target weight of 10.5 . I think the OS 120 4st is probably the lightest, easiest bet in your case. If its low on power, strap on an OS 160 or a YS 110-140

A few of my club members had this plane and all were disappointed as it builds heavy. One had an O.S. 1.20AX (2-stroke) and was not happy with the power. I'd agree with nitrowing in that a YS 1.40 to 1.60 is in the right ballpark, O.S. 1.60FX is also a good choice and one of my favorite engines, Saito 1.80. You would probably need a 40cc gasser, which will be heavy.

Hey Sess! I see you're in West Caldwell. Where do you fly?

I have flown this plane with a Zenoah 20cc ei and it was just not enough and was too heavy. I then flew the same plane with an OS 1.20 2 stoke and a 17x6 prop and it was great. Unlimited virtical and hovering at about 1/2 throttle. It is a difficult plane to 3D with though but it's flat spins are great.

A buddy of mine has the same plane with a zenoah 20. It flyies fine. hover and near full throttle but has good vertical. i really dont want a zenoah though. I know each persons idea of enough power differs. I dont need it to hover or harrier, just fly good. The plane may be bad from the git go.</p>

Are the YS's alot more powerful than the saitos and os?

Another consideration might be balance requirements. If it looks like its going to come out tail heavy, this would be a good chance to throw in some extra power. I have the O.S. 160 two stroke and the 120 AX. Both really nice motors. I had the 160 in a Giles that weighed around 11 lb. Tons of power. I know you said you didn't need hovering power. I take that to mean the kind of power that lets you pull out of a hover with authority. Even so, I think the 120AX might not be what you're looking for. As stated above, its been tried in this plane and found wanting.
Anyway, just my 2 cents, from a two stroke perspective.

I may go the 160 route. What kinda fuel consumption ??

Kind of depends how you fly. Boring holes in the sky eats up fuel. In 3D work, I've found a ship with plenty of power to be fairly easy on the fuel, simply because you're not flying full bore all the time. Watch someone flying 3D with a good power to weight ratio. You'll see lots of blipping and throttle adjustment. Kind of the same principle as running higher nitro runs cooler than lower, because you can run the engine richer to develop the same power.

Having said all that, the 160 is a big motor and will go through the fuel. Sorry I don't remember exactly how much, maybe somebody else will. I haven't flown that motor in some time.

The OS 1.60 FX is a great engine. I have two. The fuel consumption is not bad at all but if your used to little .46 to .60's then you may be a little shocked at first. One of my 1.60's is listed in the RCU market place right now if your serious about going that route. I still feel the 1.20 is about perfect for that plane though.

ro347: I fly in Moonachie at the Hackensack Valley Flyers.

I have an O.S. 1.60FX in my GP Su-31 which weighs about 11.5 pounds fueled. I can get (I sh*t you not) about a 17 minute flight (full 3D) out of that engine and the stock tank and have time to spare. I set my timer for 8 minutes and land with half a tank and I have the motor set rich. Like Mr67Stang says, you will be very surprised at how miserly it sips fuel. YS's are powerhouses but they gulp fuel.

Once set properly the 1.6 is very good on fuel, a couple of clicks more rich ,and the tank empties quicker..
I also can fly 10+ minutes with a bunch left (stock tank) in an EF Yak 54.
The OS 1.6 runs strong on 5-15% cheaper fuel.

YS out pulls most engines in displacement, but wants a minimum of 20% fuel and can be a bit trickier in tuning. The sound is very exotic and powerful though. They are $$
The OS 160 can fly a wide range of larger aircraft.

I think its still the best value between glow and gas (26-30cc) engines
A Bisson or Slimline pitts muffler is usually used, and many use the VP-30 pump for ultra reliable no sag performance.

OK   Let me ask this.......in yalls opinion will the OS 120 4 stroke fly it safely? I mean like scale like or will it take a mile of runway to lift it airborne? </p>

I think it will fly the plane fine, but you won't have great 3D performance. If you are just going to fly sport and stay away from low level hovers you will be good.