Originally Posted by
automator
I am still trying to get a grasp on understanding engines and I'm sure a similar question has been asked but after reading quite a bit of several threads I still have to ask. What, if any, are some general guidelines for shimming a head for the different nitro contents? Are there somewhat specific shim ranges for a certain nitro content? I run at sea level and anywhere from 80-100F degrees air temp. Novarossi .21 engines.
As a general rule you can say that .21 engines come from the factory shimmed for 25% nitro at sea level.
- every 10% increase in nitro content, needs an additional 0.1mm headshim.
- every 10% decrease in nitro content, needs 0.1mm less headshims.