Sorry, should have mentioned the fuel - 25%

I have cut and pasted the complete post from Massive Mods on Go engine shimming below. Anything you need to know should be in here.
Just out of interest I went to a total of .5 mm initially and found after a days racing the coil of the RB#5 plug was quite distorted, which is why I have gone out to .6 mm total. Have run 2 x 3 day meetings and a one day meeting since changing to .6 mm and have had no plug issues at all.


¨Go Engine Shimming 101

The Go head button has a step already built into the head button which is .5 mm so whatever you add make sure you realise that it includes the step.

HOWEVER !

the top of piston to top edge of sleeve at TDC is 3.3 mm

from head button step to end of geo dome is 3 mm

so lets say you didnt use any shims your head clearence would be .3 mm

now whenever you add a shim you add it to the already existing .3

eg if you add a .2 your total head squish would be .5 because you are adding to the alreay built in gap of .3

I run .1 in mine to give me .4 total this was after i ran it in , before during run in i ran .4 to make a total of .7 i only ever use 20% nitro in my race fuel.

When the engine is new i recommend for the first 5 litres or first gal and a half ( for imperially impared ) Running .4 to .6 shim

This will save your plugs and give you a better idle , it will also help with relieving tension on the rod when the engine is still tight ..

So lets just talk about head shims VS Nitro % age and assume the engine is run in. Plug choice is next to each one

15 % .2 Hot
20 % .3 to .4 Med hot
25 % .4 to .5 Med
30 % .5 to .7 Med Cold

My set up on my MG66 FT is this

Shim .1mm and 20% nitro, with med plug LRP #6 , 9.2 mm custom venturi 11.5 mins tank time at average tune , 12.4 mins at race tune. 125 ml; tank. EPA wide open. Turbo Head Button.

Shims VS Heat Emissivity.

The more shims you run the lower the comp ratio, less tank time, and the cooler your head will run but this will give you hotter exhaust temps so if you are melting bodies thats why !

Less shims = higher comp = hotter head button and heat sink = Cooler exhaust temps = not melted body , better tank time..

Hope this info helps !

Cheers MM¨