for a 430hps your probably need a good amount more than a 4inch exhaust. hps puts out alot of heat. in my 2'x2'x3' box with 150hps i have a 180cfm exhaust and 4inch inline fan for intake. now that might be a little overkill but my temps are always the same inside the box as in the house because the air doesn't have time to heat up. pc fans work for small boxes with cfls or maybe a 70hps but you will need alot more than a pc fan for a 430hps