i have an ls block that i am building w. pstons rods block guard and head studs. i have heard that if u run stock sleeves w. forged pistons u need to bore the sleeves to 81.5mm, is this true?

 

it all depends on the size of the pistons.

 

is it ok to run 81mm pistons w. 81mm stock sleeves

 

yes it is

 

the reason for boring to 81.5mm is because.
When doing a rebuild, the next step up from stock for hone/bore is 81.5mm
You should bore to 81.5mm so the proper clearances can be measured to the piston spec. With a proper hone/bore your rings will seat well and the pistons will fit in the cylinders properly.

 

People usually go .20 over to make sure the bore of the cylinder is true. When I did my build I bought stock bore pistons size. It ended up my cylinder wall was just a tad bit out of spec so I had to go through the hassle of selling the my stock bore pistons for some .20 overs.

GL