Is there a chart or such that shows 2 cyl vs 4 cyl engine output ie hp etc? how does a 1.50 4 cyl compare to a 2cyl in size specs cc and hp? How does a 1.50- 1.80 4cyl compare to a 1.35 Moki ? Thanks for any info you can give. I tried to search for an answer but found very little I may not be asking the right search question or format. Thanks again.

You didn't find anything because that's a really hard comparison to make. It's hard to make broad comparisons like that like because engines can vary from manufacturers. For instance to make a point, an OS 120 4-stroke doesn't compare to an YS 120 4-stroke. Even in the same manufacturers it can vary, an OS 46 LA doesn't put out near the power that an OS 46 AX does. Because of this it's next to impossible to make comparisons based on just size. You almost have to state specific engines that you want to compare, and from that you can gather comparisons.

Ken

Thanks for the reply Ken.

Hi,
Although for strokes are fine engines, as a rule they are somewhat more complex and expensive than two cycle engines. Because of this they are not so often recomended for beginers. Unless you are required to start with a four cycle or already own one I would go two cycle. The 2 cycle's power to weight ratio is better as well. My 2 cents worth

I already own the Moki 1.35 and just didn't want to overpower the plane when it calls for a 1.50 to 1.80 4 cycle. Thanks for the reply.

You typically add ~50% to the engine displacement when going from 2 cycle to 4 cycle nitro engines. That's just a "rule of thumb", as mentioned above, different engines of the same size can perform quite differently. Some examples of the 50% scale up: a 40 sized planes take .46 sized 2-strokes, and .70 sized 4 -strokes. 60 sized planes take .60 2-strokes and .90 4-strokes. So a 1.8 4-stroke could be scaled down to about 1.2 2-stroke. Your Moki 1.34 should be fine. I've got a Twist 150 that specs a 1.25-1.8 4-stroke. My Super Tigre 1.4 flies it with plenty of power to spare, and I've heard that even an OS 1.2 has plenty of power for the Twist 150.

The Twist 150 is what I am installing the Moki on. The price of the plane was to good to pass up. So the Moki is going back into use on the Twist thanks for all the responses.

Yeah, the 150 sized Twist is cheaper than the .60 and .40 sized Twists!

I guess they've got several 150s in stock, but the .40 and .60 sizes are ordered from the factory in China, and there's a pretty wicked price increase for Chinese ARFs now.

I've got the .60 and 150 sized Twists, they are both excellent planes. I recently crashed my 150 and bent the crank on my Super Tigre 1.4 (G-2300), so I grabbed another Twist 150 ARF before the price goes up, and I plan to put an OS 160 in the new one. I could spend $70 and fix the ST engine, but it never did run very well. I always wished I had just shelled out the extra $$$ for an OS, so now's my chance to do just that!

Although we all knew what you meant, 4 cyl. means 4 cylinder. [sm=thumbup.gif]

Sorry for the wrong abbreviation. Please fill me in on the proper RCU term for 2 cycle and 4 cycle.

You just did. You could also use stroke.

Two or four cycle is incorrect as in our applications an engine can have only one operating cycle.

Two or four stroke is the more accurate way to indicate the operating cycle.

John

2S and 4S are the shortest commonly recognized acronyms for two stroke and four stroke, which may come in handy if you're not a touch-typist.

The "50% extra displacement rule" probably no longer holds true, if it ever did. I've flown the same airframe with a .46 2-stroke and a .52 4-stroke on it, and the .52 4-stroke flew the plane every bit as fast or faster than the .46 2-stroke. O.S. Max is promoting the F82-a as the ideal 4S for .60-size airframes. Enya 4-strokes were designed to be higher revving than most other brands and by reputation normally replace 2 strokes of equal displacement.

On the other hand, some of the most popular Saito engines for .60-size airframes are the 1.00, the 1.15, and the 1.25. Saitos are plenty powerful in their own right, and a lot of scale pilots will use the .72 and .82 on .60-size airframes. The Saito 1.00, 1.15, and 1.25 are similar in weight to a number of .61 2 strokes. 3D pilots use them because they balance out their .60-size airframes while providing gobs of power.

From these examples, you can see that displacement increases as low as 20% to 30% will provide similar or better performance when converting from 2S to 4S, while at the same time some pilots will go as high as 108% of recommended 2S displacement while selecting a 4 stroke.

How you want to fly the plane, how you want to prop the plane, how you want to balance the plane, what brand of four stroke engine you're planning on purchasing, what kind of fuel you're planning on flying with, and several other considerations all come into play when trying to select a four stroke engine for your airframe. A simple chart or ballpark displacement increase simply can't guarantee satisfactory results.

You need to talk to folks who own similar airplanes and get an idea of how they answered these same questions when selecting an engine. It takes a little bit of research to make an informed decision, but that's why we're all here on RCU, to help each other out and to learn from one another.

Once you get over 1cu inch displacement you will find that many 4S engines actually have more power than 2S engines of the same size. So, there is a good chance many of the 4S engines in the 1.50-1.80 suggested range for the twist will be more powerful than moki 1.35, not the other way as some have suggested here.

This is because the comparison is not linear across displacement, so statements like "50% increase" needs to be qualified with a size range. There really are simply too many variations between engines to make any useful generic comparison on 2S/4S displacement. I'd you point back to RCKen's response.