Replacing Cylinder Heads?

[dolsen]

I have a 351 Windsor in a 1990 ski nautique. The existing heads are not GT-40, they are just base heads. I have had a hard time finding a replacement for the base heads and was thinking about upgrading to GT-40. My first question is whether you need to use higher octance fuel when upgrading to standard automotive GT40's, because I understand that the combustion chamber is larger in the base GT40's as opposed to the GT40 P's. Secondly I was wondering if anybody has succesfully installed the GT-40P's, without any problems with the exhaust manifold.

[83sn2001]

I think it is a direct bolt on but I have never swap any out. If you get a set off of a car you may have to have the bolt holes drilled out, but that is all that I am aware of. You might want to look at changing the cam to the gt-40 grind to get the full potential out of the change over.

[dolsen]

Thanks for the advice. I was wondering if the base GT-40 that came on the 93-95 Ford Cobra/Lightning was the same as the marine GT-40 except for the bolt holes?

[darrel409]

Go to the Correctcraftfan.com site they have had multiple discussions regarding your proposed swap recently. 83sn2001 is right about the cam switch too, design your engine improvements with direction and purpose. They also have a set of gt40p heads w/ the bolt holes already drilled out that just went up for sale on that site. Good price $700 for the new pair.

[siuski]

I upgraded the heads on my 93 last year. I ran 87 all last year (my dealer said it was fine) with no problems. The extra hp is very noticable. I didn't change my prop. I can provide a much better pull for jumpers, slalom, and wakeboarders now. My dealer did the install, but he had no problems with the exhaust.

[dolsen]

Thanks for the encouragement. I didn't want to have to run 93 octance all the time due to upgrading to gt-40p's. I currently run 89 and hope that that will be sufficient. The gt-40p's appear to be more readily available then the standard gt-40's. My intuition was to go with the newer gt-40p's, but since the combustion chamber is smaller I was concerned about having to use the high grade fuel. I appreciate all your help.