Correct me if i'm wrong,

120 means 1.2 ci, 1 ci= 16.3somthing cc, so 1.2ci = 19,56 cc

so .90 2 stroke is 14.67 cc

.60 2 stroke is 9.78 cc And so on....

therefore, 120 4 stroke is the same as 120 2 stroke ( in capacity), the diffrence is, that 4 stroke would have much more tourqe than 2 stroke making it able to pull larger diameter props.

TC[8D]

Min:

The ratio is 3:50. A 50cc engine is 3 cid, an engine of 0.15cid is 2.5cc.

Going between 2s and 4s is more complex. The two stroke engine usually can turn a lot more rpm than the 4s, rpm generally equals horsepower. But the two stroke does not get to use its entire displacement for power, the effective displacement, from the time the cylinder ports close is about 30%-40% less than the numeric displacement. And the effective stroke is reduced as well. Again a generality, longer stroke means higher torque.

So, the two stroke wins the horespower side, the four stroke wins the torque race. Then add the note that the peak horsepower of the 2s is often at an impractically high rpm, we have to decide the only place the four stroke engine loses is in a racing plane. The 4s also loses the price war, but that's outside our consideration of the moment.

Bill.

I am getting back in to flying after 8 years. All though I have flown alot and always used 2 strokes. I took my first two stroke apart and rebuilt it at the age of 7. I am very comportable with them. I have never touched a 4 stroke. It seems like they are really better for the sport flyer and to start learning 3d.

my question is?..is the transition hard. how much diff. is there in the every ay use? Where can I learn more about them?

Stew:

There are many threads here about maintenance, repair, and general care and feeding of four stroke engines.

If you are comfortable running the two stroke engines you shouldn't have any great problem running a four stroke engine.

It would be best if you got with another flier in your area who is already running them, there's enough difference that you can run into trouble. On the other hand, if you read, understand, and follow the written instructions that come with the engine you should do fine.

Bill.

thanks Bill, yea this site is great. I will look up some more info. I just think the benefits of the better torque are just to good. And I always like to learn somthin' new.

I'd put my Os 1.08 2 stroke up aganst any 1.20 4 stroke for hp, I have a 1.20 magnum 4 stroke, it doesnt have the power or the rpm to match the 1.08, this engine can spin an 18X6 prop although i use a 16X6 , my 1.20 is rated for 12,000 rpm, the 1.08 16,000 rpm @ 3 hp (14x6)..