gt-40 head?

hello everyone,i was wondering what modifications need to be done when using automotive gt-40 or gt-40p heads on a marine 351 besides changing to brass freeze plugs.thanks for all replies

As Gary mentioned, you'll need to have the bolt holes drilled out to 1/2 inch for the larger bolts used on your 351. After you swap the heads, it is also a good idea to replace the bolts with a new set of ARP bolts rather than reusing your old ones.

the only thing i can think of also, not being the big Ford guy is, i did have a couple of pairs of truly marinized GT heads, both intake and exhaust valves were stainless...obviously put in the heads for higher heat ranges???? but, do automotive GT's get the stainless? I dont know

not to hijack.... but what would be the HP gain from just the heads would you feel a difference ? top end speed increase ?

Dan keep in mind your experience may differ,but I had no top end difference at all.However it does seem to have more mid range torque.I have a 302 and a good cam but am using a 450 cfm carb.My next step is to put on a 650 and see what that does.

Gary S wrote: Dan keep in mind your experience may differ,but I had no top end difference at all.However it does seem to have more mid range torque.I have a 302 and a good cam but am using a 450 cfm carb.My next step is to put on a 650 and see what that does.

Gary, I still think your engine combo has issues... though Im not sure what they could be, exactly. Maybe a less than optimum cam?

My sister swapped a set of P heads on her Mustang last summer, added an RPM intake and a Speedpro cam from Reid. Still running the small outlet (2-3/8") Interceptor logs, but the rest of the exhaust was upgraded to 3"... With some soaked foam and a slipping transmission, the boat still managed to hit 49.5 on the gps. Im certain that number will be improved upon this year with a fresh trans. We did slap a 600cfm Holley onto it though- so maybe youre heading in the right direction with that swap.

Gary S wrote: That speed Tim is just with me on board so I don't really know how much of a difference that makes.No foam,3" exhaust,Holley Contender manifold and that 450 carb.I miss spoke I have a 600 I need to rebuild that another member kindly gave me(thanks Andrew).I'll mess with it this spring,right now I don't want to change anything before the big trip.Here is the cam card,the firing order is wrong,I wonder now if anything else is too! What do you think of the specs?

I cant comment on the valve timing (it would need to be plugged into some dyno software) but the lift looks pretty healthy. Maybe someone could run the program for you and see what type of hp you should be expecting. I do think that the 600cfm carb is the way to go on a warmed up 302 though- so if I were you, Id be inclined to rebuild it and bring it with me to FL to try on the water! Sage had none of the too-large-carb symptoms with the 600cfm Holley on her 289/302... great idle, off idle and all around performance.