FYI: Those are glow engines. I'm know you already know this. As a friendly reminder, you should refer to them as glow not gas. When you say gas, 99% of the modeling community will assume you mean gasoline. This is important becasue glow fuel is very different from gasoline and there are both types of engines in our hobby.

Most glow engines, becasue of the high oil% in the fuel, will leave a small smoke trail. The saito 100 should smoke noticibly, mainly becasue of the quantity of fuel it burns compared to say your OS46. You can add extra oil to the fuel, but considering most fuels are around 18% oil already, you really can't add very much more, so it really won't make a big differance. And as you add oil, you will reduce power since the oil will reduce the % of nitro and alcohol. Really, the only reason to add extra oil to glow fuel is to increase lubrication. Any oil that is added needs to be soluable in alcohol and nitro. My suggestion is Klotz Heliglow or Klotz Benol (castor) which can be bought online at klotzlube.com. But again, it won't increase your smoke much.

If you really want to smoke, you need to use smoke oil in a seperate tank and inject it into the muffler. I suggest SuperDri Aviation smoke oil, but other stuff exitis. DON'T put smoke oil in your fuel... you don't want that stuff running thru your engine. Smoke mufflers for glow work best if they are designed as such with a preheat chamber. Smoke takes heat to work properly. More heat = more smoke. To really bellow smoke out, you need a hot exhaust, like what gasoline produces. Next best smoke would come from a large glow 4S. The least smoke will come from a 2S glow as 2S exhaust is fairly cool compared to 4S and gasoline. I wouldn't bother on the OS46, but you might get reasonable smoke on the Saito100 with a good smoke mufler. I've never had a Saito so I'm not sure who makes a smoke muffler for the 100, but someone must. Depending upon your engine and setup, you may have to pump the oil into the muffler with a smoke pump, such as a TME smoke pump. OR, oher delivery systems work on crank pressure and require a on/off valve.

Another key to produciung good smoke is to fly slow at high power. This typically means using large diameter low pitch props. The slower you can fly at high power settings the denser the smoke will be.

Cheers.