Well.....2 stroke equals firing everytime the piston reaches TDC.
4 stroke (as the name implies) fires every OTHER time the piston reaches TDC. Hence, better fuel economy.

The reason for that is that a 6o 2-stroke is comparable to a 90 4-stroke. If you look at an airplanes specs, it will usually say something like:

Engine size:
60 - 90 (2-stroke)
90 - 120 (4-stroke)

No doubt about it, 2-strokes are smaller with more power-to-weight ratio than 4's.

4's are just so sweet. But for a beginner, I'd stick with a 2.

A .60 two stroke is not comparable to a .90 four stroke! The four stroke is more powerfull! Years ago they allowed the pattern guys to use 15cc sized 4 strokes while the limit for two strokes was 10 cc. Well at the time maybe they were comparable but with the next generation of 4 strokes (which came out immediatly after this rulling) the pattern guys switched to the 4-strokes. A typical sport .60 is probably more compareable to a .80 4-stroke.

This is quite correct,

if money is not a problem you may be better off
buying a 91 4 stroke instead of a 61 2 stroke since they pretty much very similar in size nowadays, Saito is even lighter.

With the 91 4 stroke you will be able to turn a 14" prop
rather than a 12" with a 2 stroke.
Having more torque also means more flexibility in prop/pitch choices across the power band.

I took a Magnum 46 out of my Extra and replaced it with a Saito 56 and had to add weight to the nose, that surprised me. My Extra now is a fun plane to fly. I agree with Minn I won't buy another 2 stroke because I love sound of 4 stroke. I bought an OS160 twin for my Stinson, I can't wait to hear that. Another thing I like about my Saito 4 strokes is if I just want to putput around I run 15% when I want to rip I run 30%, yeeehaaa

The same size 2 stroke is heavier than a four stroke because of the heavy stock muffler. Also manufactures make the two strokes much heavier than they used to.

I find 4-strokes respond quicker (the plane in flight) because they produce all their power right away, low in the RPM range compared to a 2C. This helps the plane speed up quickly - almost the same as a large diesel-powered truck's low-end grunt as opposed to a small car's higher top end, but slower 'off the line' punch.

It may not seem important, but one weird thing I find with 4-C's is they also -slow down- quicker. Dunno what to make of this, but it can be useful - maybe something to do with a larger prop? But I'm not sure.

OK. The winner to me is always going to be a 4-C. I don't care what the box your ride came in says - a .60 2C and a .91 4C DO NOT NOT NOT NOT make the same amount of power. TRUST ME. If they -DID- someone explain to my why my lead-sled YS .91 blows my US-60 straight to mars, while my .65 Magnum just kinda tugs it around the sky? I'm propped RIGHT ON for my .65, and probably a little under-propped for the .91. With the 91 i have unlimited vertical, with the .65 I have vertical... sort of.

For your trainer. Go with a 2-stroke (2-strokes and 4-strokes compete evenly when smacked into pavement at 60mph). For your max-velocity race planes - go 2-stroke. For -everything- else there is bound to be a suitable 4-stroke that you'll be happier with over a 2-stroke.

Uhhh.... Like.... That there YS is supercharged, dood.
Compare it to a supercharged .61 2-stroker.

With the help of a couple small turbos, my little 3 liter auto engine puts out about 450 horsepower. Wouldn't be fair to compare that to a 2-liter 2-stroke normally aspirated engine, would it?

True, I had an OS 91 Surpass on my Skybolt and it flew well. 4 years ago, I switched it to a YS 91AC, and now the thing is a rocketship! Woo Hoooo!

And BWT, rc-sport, you're gonna LOVE the sound of that 160 twin!!

Yea Iknow Minn, now I just have to find someone to finish building it for me.

I use all 4 stroke engines and have no tank larger than 10oz.
they are much cleaner, quieter, and for my money just as relieable
I have never ran out of fuel My biggest engine is .91 as I don't see much use in spending large amounts of money on big engines When I can have just as much fun with 40 to 91 size

rc-sport,

Well, it won't be long before winter is here. That should give you a little more time to build.

BTW, I hear there's a big show coming up in Chicago. Where can I find some info?

Minnflyer, You mentioned in two of your post that 4 strokes are cleaner.



That's totally the opposite on my end, I find that the 4 strokes make more then double the mess on my planes then my two strokes do.


Now maybe its just the smaller four strokes that are cleaner or maybe its the brand of 4 stroke, who knows as I run 100's and up. I have three, 2 strokes and two four strokes and the 4's leave by far more of a glob of waste on my plane then my two strokes do. Maybe its because they have to run richer then the two strokes *shrugs* I have one Saito 100 and one OS 120 FS that has yet to be fired up. All I can tell you is my Saito 100 leaves a pile of gue on the bottom of my Edge.

Randy

Minn, the show coming up is the RCHTA show on Sept 8th, I believe. Its one day only open to the public, it used to be 2 days. Its held at the Rosemont Convention Center in Rosement, plenty of hotels in the area. When I get more info I'll let you know.

'Da 65 iz piped man And that's not a supercharger per se, but it crams air into the engine... so I guess it has resemblences....

My 4 st's are much cleaner than 2 st's There are times when I don't even clean my planes after flying. I guess it depends on where you point the exhaust.

I think you hit the nail on the head rctrax. Blackie, you must have just the right combination of where your exhaust is pointed along with the aerodynamics of your planes.

I use mostly OS 70 Surpass, OS 91 Surpass, and YS 91AC.

For 2 strokes, I use mostly 40-50 sizes.

Like rctrax says, most of the time I don't even clean my 4 stroke planes, whereas my 2 strokes (and I'm not running them rich) will have a stream of thick oil, 2 or 3" wide, running the entire length of the plane.

With my YS91AC, blowing smoke between the bipe's wings, it still doesn't leave nearly as much oil as the 2 strokes do.

And thanks for the info rc_sport

Actually its exhausted inside the cawl I had to cut a large hole out the bottom and I just amied it down. That may be the reason why its ail over the bottom of my plane. I also neglected to mention that I am running a high oil content of fuel. YS 20/20 Power Master.

Randy

Maybe that's it. I run Cool Power 15% in everything, 2 or 4 stroke.

If I am not mistaking the OS will be more forgiven as far as fuel consumption goes. I tried 15% in the Saito and it did not like it one bit. With the 20/20 on the Saito I get a smoother running and more powerful engine.

Randy

I just bought a Magnum .52 four stroke, and I have to say as far as fuel goes it uses far less than any of my 2 strokes. I'm still breaking it in now, running it sloppy rich and it still will run 23 minutes on an 8oz tank. I'm thinking of switching to a 4 oz tank. I should get around 10 minutes of flying time easily with a 4oz tank.

The only negative thing I can see about the Four stroke is it seem to vibrate a lot more than a two stroke. Just make to check your screws for tightness often.

TiggerFlyer

I think all the bases where covered to some degree in most of the posts. 4s's are heavier, larger, cost more, different to adjust and require more maintenance. Most produce power at lower rpm and can swing a larger diameter prop. IMO the OS 91 fx should run no larger prop than a 14x8 but the OS 91 surpass can swing a 16x6. 2 strokes do not usually like a big load and can get real hot. My 4 strokes sip fuel better than my 2 strokes. Note that the ST 3000 is designed to spin a large prop at lower rpm the ST 2300 a small prop at higher rpm and your pay for power in the YS by cramming more fuel into the chamber with cuts fuel economy. I prop my 4 strokes to run at about 9k on the ground but most of my 2 strokes at better than 10.5k. By all means try one but maybe your third or fourth engine. Make sure you run a 4 stroke a little rich - you don't want the prop come off from a lean detonation. 4 strokes do sound great. Each type of engine will have different characteristics.

Blackie, I switched to 30% to run in my Saitos, the difference is awesome.