Has anyone ever rigged up a cold air intake for their engines? It worked for for my M3. Why wouldn't it work? why not plumb cold air from one or 2 of the vents directly to the intake? I have 454 mag mpi's and was thinking running some a duct to one of the vents. Seems to me the engines would get fresh air from outside of the boat and if I run large enough ducts, it would not hinder performance..but may increase it.

Seems to me the vents on my 31ss are sort of pointless. there are 4 on each side. Three of them are well ahead of the engine compartment and the one nearest the engine compartment..which is actually in front of the engines is ducting air out..the other three scoop air in. There are no vents in the back of the boat.

What are your thoughts?

Couldn't hurt to try, although I doubt you'll see a performance difference unless you rig a ram air set up. I don't think there's any shortage of fresh air is the engine compartment.

Is that the same thing when people run with the hatch up about 2 or 3 inches?

I would try that before you spend all the time and money on duct work.

The center cushion of your rear upright back bench is removeable. Pull it out and try that first to see if it helps. With the 500 and 575's it seems to let them breathe better.