Base gasket

do you use the different base gasket thickness to change piston squiss or port timing or does it effect both?

Squish. As far I know nothing else.

Base gasket will affect both squish and port timing. Some engines use base gaskets to set port timing, and copper/brass head shims to set squish.

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Base gasket thickness affects affects both port timing and squish clearance. Depending on the engine and rules, you may use a combination of base and head gaskets along with machining to get the desired result.

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running an x30, i see base gasket listed for sale but have not found head gasket??

x30’s use rubber o-rings.

So the only way to increase compression / tighter squish without changing exhaust timing would be to modify / mill the head?

This is the kind of head gasket I was referring to.
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But mechanically you would have to machine the head, top of the cylinder or both to reduce squish clearance without changing port timing.

I’m not sure what the rules are for X30.

I have just taken the head and cylinder off my X30 for general maintenance and replaced all the o rings and fitted a new 0.4mm cylinder head gasket.
The gaskets that were in place were 2 film gaskets (stamped IAME), combined thickness approx 0.2mm.
What will be the impact of the thicker gasket on the engine performance?
The engine was running sweet so dont want to change things too much.

I would expect that your engine now would be way over on squish (less power) and have a later power curve. So while it probably won’t be really bad, I would expect it to be “more” sluggish than before.
I would be interested to know if you can feel the difference if all you have done is change gaskets and O-ring and no honing or piston change was carried out.

Moving the barrel hight around shifts the port opening and closing times and moves the squish as well. So you must be aware of the cylinder as a whole not just the base.

Moving the barrel will effectively change the power curve, ie the whole curve will move either up or down in the RPM range and absolute power will “mostly” stay the same.
Lowering the barrel will make the peak power come earlier in the rev range and making it higher will make the peak power later in the RPM range.

You would have to check what ruleset your racing organisation follows, as not all engine mods are legal in all series in all engines.
For example running that base gasket combination in my series in a KA100 would be illegal.