GX390 Head Bolt Pattern?

[Armilite]

All Bolt Patterns are Based on a Circle. What Size Head Bolts/Studs are used on the GX390? Do you put in Bigger ones for Racing?

All my 70's to 90's Old Skidoo/Rotax 2 Stroke Engines use either an 8mm Bolt/Stud and a (4 or 6) Bolt Pattern-based off either a 94mm or 100mm Bolt Circle.

The GX390 uses a (4) Bolt Pattern-based off what Circle?

Is 96mm the Largest Bore out there?

Here is a Drawing of a 110mm Bolt pattern. From photo's, it looks Larger.

 

[Armilite]

GX390 Torque Plate Concept

A Free Simple 2D CAD program that lets you view it in 3D.
www.emachineshop.com

GX390 Torque Plate Concept till I get the right Bolt Pattern Measurements.

 

[65ShelbyClone]

It's not a square pattern and the piston is not in the center. Bolts are 10mm I think.