2 stroke vs. 4 stroke sizing question
 

Is there a file or website where I can find a cross reference for equivalent power vs. size? Most planes list a range of exceptable sizes but I would like to know more about what is equiv. to one particular size. What I'm looking for is:

46 size 2 stroke is equiv. to a ??? 4 stroke, not a range of sizes.

Does manufacturers play a role as well, OS more powerful vs. Saito, etc.?

Would love to find a cross reference to print out and save.

RE: 2 stroke vs. 4 stroke sizing question
 

It's not that cut-and-dried. For example, when you say ".46 two stroke", do you mean a O.S. .46LA or the .46FX or later AX version?

As a general rule of thumb, two stroke displacement X 1.5 is a pretty close match unless the two stroke is a plain bearing economy engine like the OS FP or LA engines or if the four stroke you plan to use is a YS with built in supercharging.

RE: 2 stroke vs. 4 stroke sizing question
 

There is no chart or definitive formula. Even if someone tried to make one it would be ripped to shreds because the tester used the wrong fuel, wrong prop, wrong plug, or wrong something.

Some people say a four stroke needs to be 1.5 times the displacement of a two stroke to have equal performance. For a .46 two stroke that would be a .69 four stroke. That's probably close in many cases.

Exactly which two stroke and wich four stroke does make a difference. Every brand and type runs differently.

Also the airframe it is going on will make a difference in flight performance even though it has no impact on the engine's power output.

RE: 2 stroke vs. 4 stroke sizing question
 

My simple rule is:

40-size planes = 70 4-stroke

60-size planes = 91 4-stroke

RE: 2 stroke vs. 4 stroke sizing question
 

Those types of generalizations can be so inaccurate that in many cases they are wildly wrong. As said by many previous posters such a chart can be useless. The rules of thumb of just ten years ago really have no bering on a lot of what is out there now.

The performance distinctions between the two types of operating cycle are disappearing. There is at least one line of four strokes out there that arguably in the various displacement catagorys offer more useful power than many of the similar displacement two strokes.

John

RE: 2 stroke vs. 4 stroke sizing question
 

What line would that be?

RE: 2 stroke vs. 4 stroke sizing question
 

YS

RE: 2 stroke vs. 4 stroke sizing question
 

I have tested my OS 2 stroke 120 size (AX series) and have seen a buddies used YS 120 size, both with a 16 x 8 APC prop tach numbers are around 9,000.

It is very real to me that both kind of engines are improving, and it seems to me that even that 4 strokes have lower RPM numbers, they have an invisible torque which is in need on some emergency cases or for some 3D maneuvers.

Just a few years ago a 120 size 4 stroker engine was a very heavy and big engine,
Now the manufacturers have improved their efficiency and they are selling now those high power engines in a small lighter sizes.
I love all my 4 stroke engines but it is a truth that there are now at the market some great 2 strokers which can handle bigger props as the 4 strokers were doing for years.

RE: 2 stroke vs. 4 stroke sizing question
 

just get the biggest that you can fit and balance!:D

RE: 2 stroke vs. 4 stroke sizing question
 

The problem with making any comparison is the fact that they exibit different ability.
ie... 2 strokes are known for speed and are good for pylon racers and such, 4 strokes are known for torque and are good for aerobatics particularly those involving vertical climbing ability.

RE: 2 stroke vs. 4 stroke sizing question
 

I bought an UltraStick 40 ARF. I was originally planning to toss a .46 2-stroke engine in it but instead went with a Saito .62 4-stroke. It's hard to compare power since with one you're spinning a 10" prop at higher RPM and the other, a 12" prop at lower RPM.

The 4-stroke is definitely quieter, more expensive to purchase, not really that much more difficult to set up plus it just sounds way better.