Super Bob

Can some one explain wich cylinder head shim to use and when. I have a pack of three from traxxas thin,med, and thick. I have a 2.5 with a new piston and sleeve wich has been broken in. I used the medium shim and am burning 30% nitro.It seems that it does not have the power you would expect. I was thinking maybe a shim issue. Just trying tu get an understanding of shim selection.

J_Bone

My Feedback: (1)

Think of it this way. You shim to have the proper area of combustion. If the area is too big, you won't get the best performance out of your engine, Too small and you start detonating.
Detonating will ruin the engine by igniting prematurely and add stress to the crank and other rotating parts. A visual test to see if it's detonating is to check the top of the piston. You will start to see small pits on the top.
To alleviate the problem, you shim the head higher and try colder plugs. Only shim up with the smallest one at a time.
Plugs too don't make your engine run hot or cold. They are more of a timing of ignition than actual engine temp.

J_Bone

My Feedback: (1)

I was running my 2.5 with 30%/MC59 plug and didn't add any shim to it. It seemed to run great but still lacks power of the 3.3 or OS TM/TZ.