I have a whipped on a custom built 496 does any one know what pulleys they put on them for 3.5 lbs and 6 lbs boost. Mine ar 3.5" on top and 8" on bottom and only seeing 3.5 lbs of boost

You need a smaller pully to get 6psi. You are about where you should be for the size of the pully depending on how many RPM's you are running. What are your rpm's, size boat, prop? I am getting 6 with 2 5/8 at 5300rpm on a 509.

It is a 288 sunsation a 496 with a 26 hydromotive p5 only getting 5100 rpm

Dennis, be careful throwing boost at an 8.1 if it does not have forged pistons or crank.

It does I have a forged crank,pistons and rods dart heads it's built to take it

I measured the original 5psi pulley that came with my whipple when it was new and it is 3 1/4". Of course that is at sea level and you need to go smaller as you go up in elevation. I'm at 3200.
Good advise JRider, it sounds like Dennis has it covered but I wouldn't whipple a stock 496 either, they don't last.