Good point!

For simplicity you can always assume that you are "loosing" about 30% of power on 4 stroker. Thus, to find an equivalent for the "stated" 2 stroker just multiply the size number of the 2 stroke engine by 1.3 - that's your "about the same" size of 4 stroke engine.

For example, your kit calls for .40 size 2 stroke engine, it means you can go wit about .53 (.40*1.3) size 4-stroker.

...just my penny here.

trailingedge, I have not tried the 16x4w prop yet, but I plan on trying a 16x4. They are too skinny? Doesn't have the pulling power that you would think it should have? I am using the APC 15x6, but thought about also trying the APC 15x8 also. I am spinning the APC 15x6 around 10,200 RPM and need to get it down to around 9300 atleast. I have a MAS 15x8 that would spin at 8900 when the motor was not fully broken in, but I think it should be able to handle the prop better now. I'll have to try a normal APC 16x4 and a APC 15x8. It rained most of the day Friday and all day on Saturday down here in Jackson, but we did not get any ice which was a blessing. I flew today after work in a little gusty wind but it was fun, but still too cold on my hands. The field is still too wet for my taste.

When it warms up you should plan a trip to come to one of our fly-ins. Here is our club's web site (needs updating still). www.mmrcc.org I am the club's secretary, so my info is on the website under club officers. Feel free to contact me anytime...

Derrick (DTB)

What about economy spread out over the life of the two engines. Will a four stroke last long enough or be fuel efficient enough to make up for the difference in price? I really like the way they sound but price was a big factor for me. I might consider getting one one day if the longevity and fuel efficiency attributes of the 4 stroke lessened the price gap enough over the long run.

Caint beat a good four stroke for airplanes. The only 2 stroke i have left is a enya 40.
Quit the 2 strokes when i bought my first saito 20 years ago and she still
runs good. Now all i own is OS,SAITO, and YS four strokes in my airplanes.

I have a OS-FS-40 that I was thinking of putting in a Global ME-109 that calls for a 25-36 2 stroke,
would the FS-40 be enough for the 3.2 LB plane? This is the older FS-40. I am kind of new to 4 strokes and would like your inputs. Thanks in advance

This is to add a little more observations to the subject. I can compare two basically equivalent engines, a Saito 80 and an MDS 68. One is mounted in a Phaeton II and the other in a Hog Bipe. When tuned for flight, they both turn a 12-6 propeller approximately 12,600 rpm. The idle is set at 2,500 rpm for both. They will both idle a little slower but this is slow enough and gives dependable prompt transition. (Of course the Saito sounds much lower since there is ½ as many power strokes.)

They both start easily. The MDS can be choked by putting a finger on the intake. This won’t work on the Saito since the intake is at the rear and the cowl is in the way. However a finger over the exhaust port of the muffler works just fine. The needle valve adjustment on the Saito is further from the prop but similar locations can be had for many glow engines. The Saito has a deeper throaty sound while the MDS is more of a scream, but neither is exceptionally loud. The Saito costs $224, and the MDS $99.95. The Saito weighs 19 ounces, the MDS weighs 18.2 ounces.


Both engines turn the propeller with authority and have more than enough power to fly the airplane. As far as dependability, since the MDS is relatively new, I will consider my experience with other engines. In the last six years I have built nine R/C models with power plants ranging from a Norvell 0.61 to the Saito 80. They have included five 2-stroke, three 4-stroke engines and a diesel. During that time I have experienced several “flame outs� with each type. In every case the cause was either a fuel delivery problem or a mistuned engine. In other words I was the cause of them all. If a mechanically sound properly adjusted engine has a suitable supply of fuel, it will continue to run as long as you ask it to.

Each type engine is slightly better in some areas than another, but it is apparent to me that there is no significant technical reason to prefer one over the other. The choice really comes down to personal preference and passion.

I don't have any problem with the four strokes. As soon as they make one
that doesn't cost 2-3 times as much as a two stroke, runs when you want it to
without working on it every day and one that won't shake my airplane and radio
to pieces I'll be happy.

tommy s

I have retired all my 2 stks and now use all 4stks I now have 10 of them and love every one of them. Just be sure the valves aen't too tight.I had much trouble at first with the smaller one when I set the valves at the bottom of the tolerance window and the exaust valve got hot enough too cause it to nold open and kill the engine. It ran fine on the ground but as sone as I tried to take off it would warm up and die.Set the exaust valve to 009 and it runs like a champ.

They have answered all but the cost factor... I haven't had to touch the needle valve on my O.S. .91 FS in over 18 months (puttng several gallons through the engine.) The vibration was no problem at all... not any worse than a typical 2-stroke. the cost... well it was $250 for the engine... which is right at 3 times the cost of an equal power 2-stroke. But it burns enough less fuel... and is so much more reliable I think that made up for the cost difference.

Only problem I ever ran into with it was: I improperly tightened the muffler... and ended up stripping out the threads. ($25 for a muffler... []) My fault... not the engine's...[&:]

How many 2-strokes can you take out in any weather from 32 F to 120 F not care about the humidity... and not have to change the needle one click?

I just started flying my first 4 stroke this year, OS 91 on an Ultra Stick 60. It is so smooth. From now on the only two strokes I will buy will be gas burners, for glow fuel it will be 4 strokes. Next plane I wan't to try a YS!!

Speaking of gas...can you use regular (2 stroke) 10% nitro fuel in a 4 stroke; or do you have to use the stuff that's labeled "4-stroke fuel?"

Specifically: Saito 100 & Tower Sport 10%

Thanks.

I have a YS .91FZ. This thing is turning a APC 15x6 at 10,000. This is a serious powerhouse. If you like your OS .91, you will mess yourself with the power from a YS .91 (supercharging all the way). Just have to wrap the fuel tank to keep it from exploding, other than that, it has been no problem. Be sure to keep the valves adjusted to the proper clearance.

Sure, it will burn the 10% fine. My YS really doesn't like anything under 15% though, but you Saito will probably work maybe. The Saito 100 and my YS .91 really lives for 15%, 20% or more nitro. I normally use 10% for break-in fuel, then either use 15% or 20%. You'll probably have to use a smaller prop or same diameter with less pitch.

You would have to check the oil content of the fuel vs the oil requirement of the engine. I am unfamiliar with the Tower fuels.

The oil content of PowerMaster fuels is adequate to protect most 4-strokes if you adjust the mix a couple of clicks richer than normal on the high speed needle. (a good idea any time... is keeps the engine cooler... less wear.. less troubles.) 16% oil in the PowerMaster Sport blends.

The 10% nitro is just fine... But I have heard that Saitos like a 15% nitro blend a bit better. I run 10% and 15% in my O.S. .91 (with no notable difference... not even a needle setting change needed...)

I've never pushed my 4-stroke for max power... on the triplane I set the throttle linkages such that 80% throttle was the max I could get. (its all I needed and then some.)

Tower fuels (Wildcat with the Tower logo on the bottle?) are "at least 18%" oil content. Anyone know the minimum oil requirement for YS and Saito 4-strokes? This seems high compared to other brands so I'll assume it'll work just fine. I've heard that YS deserves nothing less than 20% nitro...is this true?

I can't speak for the Saito line, but YS is 15% min according to the manual for oil content, but I wouldn't chance it with 15%. I would go with no less than 18%. YS are powerhouse engines and the extra lubrication wouldn't hurt. I use YS 20/20 with very good results. I use this on my OS .46FX with a MCP (mousse can pipe). Vertical is unbeliable on a Super Stick with the FX up front spinning a APC 12x4 at 13,980. Back to the YS. I have used Wildcat 15/18 with good results, but the difference is very noticable compared to the YS 20/20. To me atleast. The Saito line probably can get away with using 10% nitro, but I don't believe a YS will like it much. 18% oil is the lowest I would go as far as oil content is concerned on any motor.

YS .91FZ Manual
"Use a good quality fuel which contains 15-20% nitromethane and an oil content of 15-20%. Synthetic or castor oil can be used, or a combination of synthetic and caster. Do no use four cycle fuel due to low oil content."

I never use straight castor oil. It will clog the YS up. Castor is good for break-in purposes, but synthetic is better for the engine once broken-in or a combination of synthetic and castor. A 80% synthetic and 20% castor is good.