Originally Posted by doki_doki

No need to shim this engine. It already has 2 sims installed from the factory. One shim is thicker than the other. If I remember it right, one is copper in color and the other is silver. Forgot which one is thicker thought. With the two shims installed, you can run the engine with up to 30% nitro. I ran my engine with both shims installed using a 25% nitro and it ran great. No problems so far (been running the engine for almost a year) As for running 16% nitro, you may want to remove 1 thinner shim but it depends again on the performance of the engine and the weather conditions. Why not run it with both shims installed and see how it runs. If you find the engine boggy, you can remove the thinner shim first and see how it runs...