What other mods have the inline pro guys done to get to 13:1?

 

See their website or their engine build post in the S2KI Sponsor group buy forum for their 2.5L stroker engine specs. Iron cylinder liners, 13:1 compression ratio pistons, H-beam rods, stroker crank, valvesprings and retainers. I believe they also offer high compression pistons, rods, etc. for stock crank and cylinder walls.