I have a mastercraft prostar 190 with a 351w. It has a holley carb that I just rebuilt, but I am needing some more power to barefoot. So, I was told to install gt40P heads. That being said, will the heads need to be milled for 1/2" bolt holes, and what kind of valves are best to use?

 

The boat motor should already have GT40 heads on it, it's easy enough to find out just look for capital letters on one of the outside corners near the valve cover. If you find the letters GT then you got GT heads and P versions won't be much of an upgrade, but of you find a R or T then you have regular small valve heads and GT40s would be an upgrade. Also of it turns out your motor has regular production heads then it probably also has a regular production cam and that leaves a LOT of untapped potential on the table regardless what heads you use, in that case you'll see far greater gains from just changing the cam.

 

I see numbers instead of GT. What does that mean?

 

If it's a pre 1986 motor, them you definately need a head upgrade. All the stock Ford heads after 1985 had those letters cast into the corners the Conansk pointed out. "S" denotes E6SE heads, "T" was on the E7TE's, "GT" was cast on the GT40 heads (along with three vertical bars on the end of the head) The "P" heads had either GTP or "P" cast there. You may not be able to use "P" heads with your exhaust manifolds due to the different spark plug angles. And do your research before doing a cam change, what works in a car or truck isn't necessarily what you'd want for a ski boat. Seems to me you'd want better bottomend and midrange for pulling someone up out of the water in as quick a period of time as possible.

 

The easiest way to aquire the gt40ps are from the last few years of explorer; find one in a j/y. I am in the process of rebuilding a late model roller 302 and these are on my workbench waiting to go to the shop for a quick once over as soon as they get my block back to me... The cam I am going with is out of the same exploder; i have had a fair amount of advice from these guys and from another on a boat forum... The exploder cam should produce some real nice results however... Your 351w is probably not a roller. It might not hurt to see what it takes to rollerize that shìt as it might be good for lots of bang for the buck.

This makes it easy... Put the top end in from the explorer and your in business.

Also... Not sure about your manifolds but mine are the big water jacketed types... They have lots of room. The gt40p heads work fine.