I have a stock cubed LS1 (346) w/ 90k miles and i had the cylinders honed and cleaned. Having the miles it has and with the honing , the machinst told me the walls have increased in size by just a little bit. He told me to get a set of file fit rings, which i did from speed pro (R-10598 13mm). The package came with instructions on how to file fit them, but the instructions are coming off of a 4.00 bore piston, i have the stock 3.89 size but a forged piston, so its a little thicker due to the coating, but not that much thicker. I am wondering what should be my piston ring gaps??? I plan on using nitrous at times. Any insight would be helpful!!! thanks

 

This is the piston kit i bought through sdpc2000 and it oringinally came with piston rings but like i said, the machinist told me to get the file fit and i did.
http://www.sdparts.com/product/KITSD...pgradeKit.aspx

 

There is normally a chart that tells you what to set the ring gap per inch of bore for different applications. Example would be, .004" for 1 inch of bore for NA. So multiply .004 x 3.89 = .0156 gap.
The difference between a 4 inch bore, and a 3.89" bore will probably be less than .001". So you could just set it for the 4" bore and be safe. You don't want to gap to close completly, it can break the ring.
The second ring doesn't need as much gap.