Hello, I'm going to be picking up a set of GT40P heads off an Explorer/Mountaineer very soon and I'm having difficulties finding if there is anything that will need to be done to the heads before they can be swapped onto my 351w. Will I need new springs? I know that I will probably have to enlarge the bolt holes to 1/2. Should I lap the valves?

Here is what I'm trying to do, I've gathered a lot of the parts. Once I have them all in hand I'd like to swap out the heads and intake/carb all at once. Currently running the stock 2bbl, with the Motocraft 2150 (with massive vacuum leaks - the truck won't idle properly).

351w
GT40P heads
Stock iron 4bbl intake
Edelbrock 1406
33" tires
3.55 Dana 61

The truck will be used on the street, hauling heavy loads, pulling trailers, etc. I frequently load up the bed with very heavy objects! It's what the truck is for, right!?!

 

Those GT40P springs are designed for the explorer hydraulic roller camshaft and will probably be too much pressure for a flat tappet cam if that is what you have being a 1983 model. You really need to know what cam you have in there and match the springs accordingly if you're keeping the cam. Also those gt40p springs are lift limited if you have or will be installing a higher lift cam. Most people will tell you to have the heads checked out by a shop which is always a good idea because it is a crap shoot. Look closely at the mating surfaces (straightedge helps), seats/valves, guides, etc. Yes the 351 will require 1/2' bolts I believe. I've always installed P's on 5.0 engines. Personally I have ran heads that I have picked up but they were low mile, clean, and visually checked out OK but I've always changed out the springs to match my usually larger cam.

 

I'm not entirely sure what all the specifics of engine in the truck, but I'm fairly certain the cam would be a stock cam. I don't believe it's the original engine, and all of the emissions and engine control were ripped out. Just using Duraspark II and a standard vacuum advance distributor. My plan is to find a set of heads off a junk yard Explorer/Mountaineer this weekend.

 

If you are serious about using this truck to haul heavy loads, I would put a smaller tire on it. 3.55's with 33 inch tires are not the best combo for hauling loads. Plus it sits the truck up so high making it harder to load.

 

I'm very aware of this fact! I love the way the truck looks and I'm still young enough to climb in and out of it (for now......). Once/if these tires need replacing I'll go back to a more stock size but I'm pretty sure these tires will last longer than I'll own the truck. This truck is mostly acting as a farm/beater truck. Dump runs, furniture, wood, gravel, etc.

I'm mostly hoping to get it running better, right now I have to use both feet to drive even though it's an automatic. If I don't flutter the gas pedal at idle it will die, other times I'll come to a stop and the engine will race. If I don't hold down on the brake while I'm fluttering the gas pedal I'm sure I'd 4x4 my way right on top of the car in front of me.

I'm fairly certain there is a large vacuum leak at the butterfly shaft on my 2150 so the 4bbl intake and carb will probably solve my problems but if I'm going to have the intake off, I figured I might as well keep going and take the heads too. Ohh, and the radiator is plugged up.... This truck has got me into a lot of hot water with the wife......

 

I would skip the heads for now. It's going to be a lot more work, and you won't be able to take advantage of free breathing heads with those gears and large tires. Unless you pull it down and shift it manually.

 

Thank you for the input. I'll work on the 4bbl conversion for now, and worry about the heads another time.

 

Later down the road you can keep your eye out for a old f250 or 350 sitting in someone's yard. 4.10 gears are very common in those trucks up to 1998 and the whole complete axle assembly would swap in place. The trucks to keep an eye out for are 1985.5-up f350's. They will have the dana 60 front axle that everyone is looking for to swap in their truck. There are some that do have 3.55's, so make sure they have 4.10's before you buy. Then you can do more work on your engine after that.

 

You will need the exhaust manifolds from the P heads. No idea if they will work on the full size trucks or not. You stock exhaust manifolds will not leave clearance the revised angle spark plugs.
Alternatively if you can find a set of GT 40 heads that would be the best way to go.
Do not worry about the springs the spring rate is ok for flat tappets and is in fact lower than the old flat tappet 5.0L H.O. But if you are going to use a cam other than stock they will need to be replaced as they are only good for .440" lift.

If you can sort out the exhaust I would not waste the time of doing the 4bbl then doing the heads. and basically having to redo the 4bbl set up and tuning all over again that is a waste of time money and resources.. Just do it all once.

The GT40/p heads will make a big difference in power and will help with fuel economy. Although 33's and a 3.55 rear is not ideal it will still be fine for towing all except the heaviest of loads. The 33's are only 1.3" larger in diameter than the stock size so the impact will not be that great. They will give you an effective rear end ratio of about 3.35 or there abouts.

So if you can sort out the exhaust and find a decent set of heads do the swap, you will be glad you did.

 

Why the GT40 vs GT40P heads?

 

 

Ya you nailed it. the spark plug angle on the P heads was revised to be more straight out from the head to improve combustion and help lower emissions. This can cause clearance issues with many headers and most stock manifolds. The GT40 heads use the same spark plug angle as all other factory small block heads. The GT40's and the GT40P's are pretty near identical with the P's flowing just a bit better If you can find GT40's it just makes it easier as you can use the stock manifolds and pretty much any after market header they just reduce the question if stuff will fit.