Good question!!
I'd like to hear if anybody running a marine intake on the last few years of the 5.7 vortec, like in the 1998-2000 Tahoe, and has actually passed CA smog! I'm thinking of doing a marine intake to my 383 this fall. I just had mine smogged, second time after the new 383, so I'm thinking it's time to mod!! But I think Jrgunn is right, if the truck computer is OK, and the truck passes the hydrocarbon and CO2 tests, I'm pretty sure my smog guy, who's a good guy, wouldn't really notice the marine intake. And even if he "visually" noticed a modification, if the test computer says it passed.....it passed. But I'm not sure what ECM/computer mods are need for a marine intake, if any, because I think if the vehicle ECM is moded, maybe the CA smog test computer will catch that and flunk it. That may be a CA thing. I think I've seen that a lot of folks that do that marine intake mod also do the 411 ECM mod. But I've got A LOT to learn about all this yet. This is the place!
