how much boost can a lsj handle with tuning and fuel mods?

i say 19 ish

20 with the proper cooling and fuel mods...or 17 on the stock aftercooler

how much boost can a lsj handle with tuning and fuel mods?

i'm assuming you mean with the stock M62 supercharger. Because everything is relative to what CFM your power adder is pumping out. like if you were to swap to a kenne bell s/c or even a turbo.. you would pump out less boost, but the car would be faster. that might not make sense to you, but i assure you it is true.

back to the original question, i wouldn't go past a 2.7" pulley (17-18 psi) because at that point you are way out of the effiency range of the stock s/c. (making lots of heat, and putting alot of stress on the engine)

Really, the question I have for you is, how fast do you want it to go? with this knowledge i could better help you

oh yeah i almost forgot... youre a total:
newb.....................:D

J/k

newb.....................:D