Super Jet Two base Gaskets under jug

[superjetchet21]

Alright guys. I just took this jug off and discovered it has two base gaskets I’ve never seen this before idk if it was a mistake or if there is a reason for this. The one gasket that was on the very bottom is OEM looking (basic) The other one is like a shiny plastic material that was on top of the OEM one. Has anyone seen this?

 

[///M5]

I've seen the thick plastic ones used to adjust the port timing. Never seen it combined with a stock gasket though.

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[Blue]

Some guys do it to adjust the squish clearance on cylinders that have been decked on top. You can simply buy a thicker base gasket too. Jetmaniac offers many different thicknesses. Measure the two and see what thickness they are.

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[superjetchet21]

You think If I just put an OEM one in it would be fine? Or should I try to match The thickness that was in there ?

 

[superjetchet21]

I can always put the new OEM one in and put the plastic one back on top

 

[Jr.]

Stacking gaskets is an opportunity for something to go wrong?
Buy a single thicker gasket. I stock most sizes also

 

[Blue]

You really need to check your squish to know for certain. These cylinders are usually from the 1990s and been machined many times over unless you have a newer sj motor.

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[TheBuzzard]

When I took apart a world finals winning race boat, I found 3 base gaskets and a cylinder that was ported to the moon. It had been decked on top and had custom team scream ada domes. More base gaskets raise port timing. If the motor was set up that way, you can't just start changing things and have it run right. It was set up that way for a reason. It doesn't necessarily need 2 gaskets but you can't change the thickness without affecting port timing and squish.