Not sure of their max PSI efficiency range, but lots of guys run around 15-18 psi on them with great results.

 

I'm using one on my girlfriend's 240sx, which I'm building a custom turbo set-up for. However, I'm mostly using it for the *bling* factor (she is actually somewhat into looks, go figure...crazy women) as it is all metal and polishes up nicely. Should look kinda cool in her front grill once I get it all mounted up. Of course, I am also only planning on running a max of 1 bar on her car (and that's with race gas) IF that. I'm sure it could handle ~20 psi, but I know for a fact her motor won't! :P IMO it's a "decent" but overrated IC, and getting hard to find for cheap. I'd much rather sell it on ebay, but she likes it. :shrug:

Most JY IC's have plastic endtanks that are clamped on - they typically start coming apart or at least having problems after ~16 psi. On the MKIV IC, you can run 20+ psi after using metal strapping to "wrap" the IC up and keep the endtanks from bellowing out. Many of the DSM guys (including some friends of mine) replace their stock SMIC's with these, so you can do a google search and find lots of info on them.

If you are worried about the capabilites of the MKIV IC, look at how many BPU Poopra's get ~400RWHP still using them...there's a lot more than you'd think. It may not be "perfect" but if price is factored into the equation...it becomes a very sweet deal. I had plans on using one for my 88 TBird turbo before a 90mph tree encounter changed the plans for that car permanently.

 

Here is the final position of the Volvo FMIC in my 87 TII: