Hi shalo, O.S. makes more than one .15 buggy engine. There is even a large block .15. The best thing to do is go to the O.S. website and get the specs there. The car engines will not have any problem lifting the heli. They also have large heatsinks because when the car body is on there is not a lot of airflow over the engine. Do you also to have locate a clutch assembly? There are several makes that should work as well......with your choice of gear size.
Mark

The Hitec 5245 mini digital servos have 61oz of torque @ .16 on 4.8v. and weigh only 1.12 oz. And the HS81 for throttle has 36oz. of torque @ .11 on 4.8v. and weigh .58oz. But they are not cheap. $50-$60 for the 5245 and about $24 for the HS81. I just happen to have a few of each laying around so thats what i'm going to use. The jury is out on the engine though. OS makes an 18 with a threaded crank shaft and side exhaust that would work perfectly (quick makes a muffler that fits an 18 with side exhaust). Its rated @ 1.35 HP. But I want to find out if either the ofna/picco/omega .21 (which is 2.1-2.3 HP and Although its a big block, should fit) can be gotten with a threaded crank? The problem I see with using the car clutch is, unless I ad a pull start, I will not be able to start it. And, the fan will not fit! If I want to use the factory starting mechanism and fan, I need a threaded crank shaft. What really looks promissing is the Sirio .23 (claimed 3 HP @ 39,000RPM) which is also a big block but it does not have a threaded shaft. It appears to be a stroked and bored 18. Perhaps I just need to weight until they make a motor like this and in the mean time use the OS.

After going to the hobby store one last time to look at motors, I've come to a conclusion. I compared the Ofna .21 "small block" and the only thing small about it was the diameter of the crank. But the case is about the same size and length as my full size NovaRossi .21 airplane engine. The Sirio, by Trinity, has a small diameter crank and a shorter crank. Although the case is wider and the head taller, If it had a threaded crank, you would only have to make an engine mount for it. makeing it the ultimate engine for the Quick 18. However, like the Ofna, it does not, as of yet, come in a threaded crank. Therefore, the only options at this time are either to use a .18 size engine, in which case the toki with a tuned pipe would not be a bad choice or shoehorn my NovaRossi .21 into the heli. So I am going to start a new thread, shoehorning a NovaRossi .21 into a Quick .18! After looking at some other helis, I think the LiteMachine would have been a better candidate for a .12-.18 size motor.

Why don't you just track down a Kyosho Concept .10?

It came stock with a .15 motor.., the OS CZ-15H

I just bought another NovaRossi engine for this heli. It is a .20 side exhaust engine. Cost was $100 so I will not feel bad when I cut the crank to fit. It does not have the power of the .21 but I think it will work fine. Also, the cooling head that I have will work on this motor. And, the bolt pattern is the same for mounting. I chose this motor because of the price and because it is side exhaust. On a pipe, it should be about 1.9hp @ 29,000. If I need more, i'll port it and bore out the carb. Next step is to shorten the hub that goes on the crank. I'm going to try and make the installation as tight as possible so that the engine hangs down as little as possible. I'll have to modify the engine mount I made by making it shorter as well. Also, the landing gear mount will have to be taller because the engine will still hang down a bit. And, I will have to trim the cooling shroud to fit the bigger cooling head. Ill try and post pics when all is done

** I really have nothing to contribute **
Except there is at least one Concept 10 with an os .15 on Ebay right now...