Hey all you race engine guys and gals. Am woundering what is the proper way to break in a motor to prepare it for racing. Also is there a target temp I should try to keep while breaking in the engine. Let me know any information you may have or wish to share. thanks for the help.

Depends on if it is a ringed engine or ABC/AAC

its a ringed super tiger 91 2 stroke

Well, I'm sure you will get lots of opinions so I may as well be first lol.

Start with fresh 10% fuel that is 20 to 22% oil. I perfer all synthetic as it burns cleaner. A new medium heat plug will be needed. Usually a OS #8 is the easiest to get but I also like K&B 1L and Enya #4. The reason for new fuel is that as fuel is exposed to atmosphere it attracts moisture. One day this summer walk around the field and look at guy's fuel jugs. You will no doubt see some with droplets around the top. That's not fuel, it's water. Fuel with moisture creates more heat and less lubrication.

Use a prop 1" less diameter then the one you will be running when the engine is broken in. In your case I would use a 12X7 APC. For speed you will want to stick with APC props. Put a good quality filter between the tank and carb.

Upon the first start make sure it is running rich but not overly so. You want to run rich but still generate moderate heat. The first expansion of the sleeve is critical. The smaller prop will lighten the load while letting the engine rev up some which contributes to the needed heat but remember not to allow the engine to run lean.


Run a few tanks through the engine while constantly changing throttle settings from a high idle to full throttle. After a few tanks you should be able to adjust to a reliable idle and fly the engine. For the remainder of the first gallon fly with a rich high end setting about 1,000 RPM from peak but do not hold the same power setting for very long. After the first gallon you can peak it a little more and start experimenting with props. Prop the engine so that at full throttle you are in the 14,000 to 15,000 RPM range without setting it too lean.


Prop selection gets a little complicated. If you have a clean airplane you will be able to reduce dia and increase pitch to go faster. On an airplane with a fair amount of drag, small dia props are not going to work so you need to go larger dia and less pitch. You kinda have to match the prop to the airplane but remember the power curve remains the same and that will peak at about 15,000 give or take.

thank you for the help.  You just commented on another forum about my os 91 that i sent to voodoo.  This is the engine i chose to replace that with.  super tiger 90