If a plane needs a 1.80 4 stroke, what size gas engine would do the job? I am not really handy with the cui to cc conversion. Thanks in advance!</p>

180 = 30.cc. So I think a 30cc gaser would do the job. 

thank you much!! time to shop for engine!

I'm not so sure on that one. It definitely isn't a direct displacement thing going from glow 2-stroke to gas 2-stroke and it may not be going from glow 4-stroke to gas 2-stroke either. You have to consider an alcahol/nitro burning 4-stroke vs. a gasoline powered 2-stroke may have different power output given a similar displacement. I could be wrong too of course.

I'd lean more towards a 40cc-45cc but that's just what comes to mind first. The type of airplane makes a big difference too. For instance, a big Cub can fly on a lot smaller engine than a smaller aerobatic plane.

6inarow, what is the size and weight of the plane? What kind of planes is it (i.e. sport, scale, aerobatic, etc.)?

Gasoline has a much higher fuel-to-air ratio than glow fuel, and thus if you compare a gas engine to a glow engine of equal displacement, the glow engine will provide more power. Based on the aerobats I've looked at over the past few months, something that a 1.80 four stroke glow would power would be happy with a 40-50cc gas engine.

Of course it depends on the type, size, and weight of the plane.

Thanks for the replies to all, the engine will be for an extra 330L that is going to have an auw of around 13 to 15 lbs, as I have been searching for engines I have found rather quickly that I need at least a 40 cc engine to make this plane fly like I want it. I know this is a beginners forum and thats not a beginners plane but the world of gas engines is a new beginning for me, so thats why I just asked the engine question..........lol. The plane was very reasonable in price but the engine does not look like it will be, so this one is going to have to go on the shelf until budget permits! Thanks to all of you for helping with the size info. pretty soon I imagine I will be asking how to setup a gas plane.........................OH MAN, thisnoob is nuts!

Your last post gives good info.....I've been flying gas for a short time now.....about a year or so......10 CC gas equals .60 2 stroke glow.....
But a plane weighing in at 15 Lbs would need a 40-45 CC gasser.......ask lots of questions because gas is different than glow in the tank set up.....plus I recommend an optic kill switch.......no direct wire feed from ignition to system...and kills the engine in case of a loss of power, and a very nice way for you to kill ignition when you want to open the choke or prime......
One more word of caution......everyone in my circle of friends has had a loss of confidence including me, when going to gas......go slow get the motor broke in with at least 3 gallons of break in gas before you start to get wild......your confidence comes back...you know your hooked when a 160 sized glow engine sounds weak 

http://www.hobbycity.com/hobbycity/s...p;ParentCat=55

There are a number of the XYengines at my club; people have nothing but good things to say about them. Iwould buy one for my next plane.

Iwould think that another downside with larger planes are the servos needed.  I would think that a plane like that would require more high torque servos, which can also get expensive (at least for me with a small pocket book)

Definitely 40cc or larger for an aerobatic plane like that. Maybe even one of the lighweight 50cc engines. Actually, they are pretty affordable compared to larger glow engines, especially 4-strokes plus they cost much less to operate in the long run. Take a look in the gas engine forum, you'll find plenty of good information there. Of course there is a little BS to wade through as well.

http://www.rcuniverse.com/forum/forumid_142/tt.htm

Chuck beat me to it but there is a lot of the info you need in the gas engine forum. When the plane calls for a 1.60 or 1.80 Ipull out a 2.4 40cc, a 50cc could often be better but a lot depends on the engine itself. Iget about the same performance with a Brison 40cc as the guys are getting with the DA 50cc but both engines are on the high end of price. There are several good gas engines being brought over from China for next to nothing compared to glow engines. Istill like the Zenoah engines with the mag ignitions but these new china dolls come with electronic ignitions and good mufflers so they are worth looking at.
Yesterday Iwas flying with a friend that has beenusing these{ {don't quote me on the make please, I can't keep them all in my head!!}} CCRP? When you see the make you will know it. It is a Chineese 26cc that sells for $180.00 with an electronic ignition and the muffler. Another friend just bought there 40cc and it didn't cost much more. Very light weight and a real little power house. Can't beat it for the money. You will hear a lot about them at the gas forum.
There are hundreds of threads about gas engine plane set up too.

I have an RCGF-50cc that I bought for $349. The thing runs outstanding, especially considering the low cost. Another one Ireally like is the Fuji BT-43ei. I hated it at first because the igniton was very noisy and caused a slot of radio/servo interference. After installing a CH ignition on it though it is just a sweet wngine. Starts super easy, runs smooth &amp; reliable, and makes respectable power. Of course it costs almost $500.

Thank you all for the great info!! hobby citys engine is 160 bucks complete! definitely worth trying, troybuilt models has the other engine for 180, not too shabby! Going to go troll around the gas engines forum and do some learning before I purchase, maybe this thing will be flying by the end of summer with these better prices. Once again, thanks to all!