Originally Posted by AzBobby
you don't need to change the shims due to nitro %. the shims is only for the combustation chamber and piston clearence during runnig from the glow plug. different percentages will not change that. just a re-tune and maybe a different glow plug from what you were running.
thanks for polluting these boards with more shitty information.
you must not run nitro, so why would you comment on something you have no experience with?
The shims are used when changing nitro percentages. When you jump from 20% to 30% you need more clearance because 30% brings in more air, which means a bigger explosion, hence the need for more room in the combustion chamber.
When you use glow plugs that have different heat ranges, then you need a slight re-tune on your motor. Every glow plug is the same length, unless you put yours in with a hammer, then I could see you needing to add a couple of shims.
Many european engines do need the addition of shims, for some reason they come prepped for 25%, even though they all run 30% across the pond too.