YS 4 stroke evolution is a funny thing. Yamada Japan is always making more powerful nd more powerful engines. The changes over the years have been to really serve the Pattern models. YS is the dominant engine in pattern competition and this is the niche that YS serves. The side benefit is that guys like you and me choose the YS engines for our sport airplanes even if you don't compete. You get that competition performance.

120SF
120SF Big Valve the name of the motor didn't change but inside it did

120AC has a big air chamber box on the back like the 91 and 110 The name AC was for Air Chamber. I believe the AC also introduced the crankshaft ring to increase the compression on the down stroke and give a better super charger affect.

Somewhere along in here the 91AC came out. It had the air box like the 120AC but was aimed at a powerplant to replace all those 61 2 strokes. See the pattern models were not really big enough to take the power or the weight of the 120's so the 91 was a drop in for a 61 2 stroke.

120NC and 120SC came out about the same time. The NC was a Non Chamber and the SC was a Super Charger basically the SC was like the AC but the Air Chamber was under the Valve cover, and the did some other mods The 120SC was the strongest of the 120's. They used a Crankshaft ring to increase the "Boost on the supercharger system. Also I believe the 120SC introduced the low speed air bleed screw on the throttle barrel. I know at one time we were plugging throttle barrels in that had the air bleed screw but not all motors had it. The 120SC was a very powerful but sometimes temperamental beast. It loved Nitro and as long as you fed it nitro it was happy. Try to run it on 15% and the needle setting became so critical that many folks struggled with the SC. It was not produced for very long although they are in high demand from guys that do the scale warbird racing. They run them on 40-50% nitro and they are awesome motors. I had one that could pull the same props and rpms as the 140's

140FZ released Basically a 120NC that was bored out and gave about the same power as the 120SC maybe a smidgen more. This engine also used the valve cover area as the airbox. It was a smooth easy to operate engine like the original 120SF and 120NC. It was lacking the crankshaft ring because it was larger bore and made more power with a smoother to operate temperament


The 91FZ was released using many of the same ideas as the 140FZ and just updated the 91 chassis. A little more power was the benefit.

140L or sometimes called the FZ-Limited. The 140Limited was the first engine to be introduced with the YS motor mount for pattern use. The Limited was to be a special limited production of the 140FZ with some hop ups to make more power and accommodate the YS engine mount. The main hop up was the crankshaft ring like on the SC and the carb throat was increased in diameter. These gave a little more power to the 140L over the 140FZ. YS also did come changes to the pistons to make them lighter and more powerful. Some of the changes worked and some of them were not as robust. This was also the time when Futaba Corp of America sold out to Great Planes and YS engine importing business was taken over by Richard Verano and Dave Shadel. So while the Limited was to be a limited time engine, it was extremely successful and Dave and Richard kept it around for a few years.

Then the 120FZ came out. This motor replaced the 120NC with lots of things that were learned on the 140FZ and 140L like the low end air bleed screw for idle adjustment. This was the easy to use 120SF or NC in a updated system like the 140FZ and 140L were using.

140DZ the first of the Direct injection motors or DINGO motors came out. This engine went through a couple years of testing. There were some hurtles to overcome do to the new fuel injection system. Before all YS engines had used the pressure regulator and not a fuel pump. Now the engine had a pump and no pressurized fuel system. This motor is the king of the 140's RPMs increased 400-500 over the best 140L you could find. Great motor I ran these things long and hard. The 140DZ replaced the 140L as the top pattern competition engine



Shortly after the 140DZ hit the market the 140FZ Sport came out. This was a replacement for the 120FZ and all those 140L's that were in the hands of the Sport flyers. This engine kept the same big bore carb of the 140L and had the new robust piston from the 140DZ but is really smooth and simple to operate. It still uses the pressure system like all the 120's and previous motors.


Along in here the 110FZ replaced the 91FZ again a bored out 91FZ and some other little updates to make it more powerful, and giving a few other features.


160DZ or the 160 Dingo is just a bored out 140 Dingo. A couple of minor changes like a better balanced crank make is smoother with less vibration. Also the bigger bore gives some more power and a bit more punch.


Future...the 170DZ is slated for production later this year in 2007. Basically its a little stronger 160DZ the change is not a bunch but the low end torque is really better than the 160 and you can run the 170- really quiet and still make the same power as the 160DZ. I have run this engine for over a year now and its very reliable and strong just like my 160's. The 170 will replace the 160 but only because it is the latest and greatest. About 90% of the parts on the 170 are the same as a 160 or the part from a 160 will work.

One big note if you have gotten this far. Most of the parts for the 120's will fit each other. The 120AC is the only one that has some major changes in it. But things like pistons and sleeves are all interchangeable for the 120's FS through the FZ

Same is true for the 140's the pistons sleeves usable in each other.

All the bearings from the 120SF through the 170DZ are the same.

In the time of these changes cam gears changed and this accounted for much of the changes if power. Example is you could stick a SF cam in the 120AC or even the 120FZ and it will run. RPMS at the very top end might be slightly different but essentially all the changes over the years either went for more power or smoother operation.

The 160 and 170DZ engines of today are still built on that same chassis as the original 120SF.

Back with the 120SF we ran 14-10 to about 14-12 props. Today we are running 17-12's and 18-10's on the 160 and 170DZ each generation gave a few hundred rpm more and so we went up in prop sizes to keep the engines in the right RPM range. Other than the DZ or Direct Injection Dingo motors they are work the same way all the way down and to include the 53 and 63.