View Full Version : GT40x heads

11-21-2009, 10:56 AM
Does anyone have experience with GT40x heads? I am thinking of upgrading my stock E heads with these to give my 351w some more hp. Has anyone done this swap? My MC is a 1990 prostar 190 with a 351w indmar, edl performer manifold, Acme 541 prop. I would love to hear your experiences on this. Would I need to switch cam aswell? What about roller rocker arms etc? Any advice appreciated....

11-21-2009, 04:29 PM
you might sacrifice some low speed torque with X heads. your best best is to get the GT40 or the GT40P heads.
remember you also need brass freeze plugs and if the heads are only made for a 302 you need to have the head bolt holes drilled to 1/2".

11-21-2009, 06:42 PM
Do a search here.It's been discuss a lot before.
Good luck!Shouldn't be too much of a big job...

11-21-2009, 09:47 PM
I made a switch to the "p" heads about two years ago and have been quite happy with the results (I also have the Edelbrock manifold). I'm not sure about what differences you'd see with the "x" heads but do know several other that have gone with the "p"s and these are guys that are pretty serious about their engines and would have done their homework.

The heads along with a bit more ignition advance will make a noticeable difference in your engine. Adding a cam will also give you additional gains, rollers can add a bit more as well. But of course the price of your engine modification project continues to climb as you add these goodies.....you'll find it can be a game that never ends.....there is always room for a little bit more. Your check book will have to determine how far you want to take things.

east tx skier
11-22-2009, 01:02 AM
The old GT40 heads they used on the HO in combination with the edelbrock performer were wonderful. I hear good things about the p heads. Sounds like they would be x x the improvement.

11-22-2009, 06:11 AM
Thanks for the great pointers. Had almost forgotten about brass freeze plugs...
One of the reasons, for me, to go GT40x rather than p is that I have to get these heads shipped to Europe (so weight is a bit of an issue (aluminum rather than cast iron.)
Why would x's sacrifice low speed torque over P's? In the end, budget beeing an isue of course, I guess it boils down to gt40p are cheaper but more expensive to ship... performance beeing more or less equal?
Also wondering if these heads' outside dimensions are exactly the same as the E's. When I swapped valve covers a while back, I noticed that there was very little room between them and the exhaust manifolds, i.e. I think I couldn't fit new heads if they are taller than the old E's.
Also, someone from Jeg's propose a KIT X ENERGY 262 351W cam along with ALM RCKR ARMS PED SBF 1.7 rocker arms. What do you think?

11-22-2009, 09:01 AM
I believe the X heads have larger runners, which will decrease velocity at lower engine speeds but flow a little better as the speed increases.
Again, not a 100% sure, but I think that is the case.

05-17-2010, 05:22 PM
For those that are interested I finally put in some GT40P's and an acme 13 propeller. 46 mph top speed and a much stronger pull. 4-5 mph gain (+ 400 rpm). Not so bad for a 1990 prostar. Was a pretty staight forward job but time consuming. Took the opportunity to clean the insides. Pistons were in good shape but accumulated a thick coating from 20+ years of service. Lacker thinner did the job though. If I can recommend anything is to take a look at boxwrench.net. Best dvd I've ever seen on rebuilding V8's! If, like me, you're not an expert mechanic it's a really good place to start before any big job on your engine.

05-17-2010, 05:32 PM
I find these motors sooo interesting. I did a 'stock' rebuild on my 351W two seasons ago, threw on Acme 13x11.5 running 47 mph on GPS in my 87 190