how much below pad should I run?

[vnvjames]

I have a 99 Cobra 190D with a 150 Merc. Efi. Running a 3 blade Tempest Plus. I just added a 8" Hydro Dynamics jack plate. I am running 4 1/2 inches below pad. The change in performance is : It is now faster out the hole than believable, runs 56.0 GPS WOT but I am throwing way too high a rooster tail, about 12 ft. high, at WOT I can only get 8 lbs of water pressure, the gauge is new so I know its correct, to get 12lbs of pressure I have to trim down, but loose speed. So~~~what to do? I have a new pair of trim extenders not installed, should I lower the jackplate and add the extenders?

[TomM]

I have a 6" plate and run about 2 3/4" below pad on my 188 with a Yamaha Pro-V 150. I get 12psi, 5700rpm and 57mph wide open with a 23M prop. My roostertail is slightly above the cowling.

Your setup sounds like it's too low but with the water pressure, you shouldn't go any lower.

Tom

[vnvjames]

Hey thanks YomM, so what is the minimum water pressure I need at WOT ?

[TomM]

I believe not less than 10 or 12psi.

Tom

[vnvjames]

thanks

[2fastr1]

It sounds like you have the motor too low. Throwing a high rooster tail means you have it trimmed too high. It shouldn`t be any higher than the top of the cowling. If you raise the motor it will bring more of the boat out of the water so you don`t have to trim it so high. Doing this means you should have the trim lower bringing your water pressure up while still bringing more of the boat out of the water with less trim.