Installing GT40P Heads on 1968 302?

[bulletpruf]

I have a 1968 302 that I plan to rebuild and install in my 69 Bronco project. It will be a mild build; stock pistons with new rings, mild hydraulic flat tappet cam, etc.

I sourced a pair of inexpensive GT40P heads a few years ago; they have a broken exhaust manifold stud or two that I'll need to remove, hence the low price of $100 for the pair.

I'll disassemble them, clean them up, check the valve job and touch it up if necessary. I'll also magnaflux them; I have a yoke and powder. And I'll check the deck for straightness and surface them if necessary.

From what I can tell, compression ratio should be somewhere around 9.3:1, which is perfect.

Any other issues to be concerned with? I know I may run into issues with headers and/or spark plug wires.

What about the springs? They should be fine, right? 110 on the seat and 310 open should work with a mild hydraulic cam.

Thanks,

Scott

 

[Timmy390]

Not knowing the spec's of the "mild cam" no one can say if the springs are good. It's my understanding the limitations of the GT40P heads are not spring pressure but lift of the cam.
The stock springs can't handle more than the stock cam.

Explorer F4TE-6250-BA Hydraulic Roller
Intake at 1.6 rocker ratio .422" lift 256 duration
Exhaust at 1.6 rocker ratio .448" lift 266 duration
1.7 rockers is .449 intake and .476 Exhaust
116 lobe separation

Tim

 

[bulletpruf]

Not knowing the spec's of the "mild cam" no one can say if the springs are good. It's my understanding the limitations of the GT40P heads are not spring pressure but lift of the cam.
The stock springs can't handle more than the stock cam.

Explorer F4TE-6250-BA Hydraulic Roller
Intake at 1.6 rocker ratio .422" lift 256 duration
Exhaust at 1.6 rocker ratio .448" lift 266 duration
1.7 rockers is .449 intake and .476 Exhaust
116 lobe separation

Tim

Tim - it's going to be a flat tappet, should be under .500 lift. If the springs are indeed 110 on the seat and 310 open (I'll check), then I'm sure these will be fine.

Thanks

 

[ntsqd]

By Timmy's numbers it looks to me like the stock springs are going to be marginal at handling the lift as you could be under .500" lift with your cam choice and still have more lift than the cam that those heads came with has.

 

[bulletpruf]

By Timmy's numbers it looks to me like the stock springs are going to be marginal at handling the lift as you could be under .500" lift with your cam choice and still have more lift than the cam that those heads came with has.

Roller lifter versus flat tappet is really an apples to oranges comparison. Roller lifters are heavier than flat tappet lifters. Also, ramps on the roller cam are steeper, so they open the valve much faster, necessitating springs with higher pressure.

I'm putting together a mild AMC 360 right now for my '72 Javelin 24 Hours of Lemons race car and I have a custom flat tappet cam with just under .500 lift. The recommended springs from Bullet Cams are almost identical to the stock GT40P springs - 110 on the seat and 300 open. Since the flat tappet cam I'll choose for the 302 will be a bit smaller (i.e., something like Comp 256H - .477/.484) the GT40P springs should be plenty stout.

I'll check the pressure on the springs just to make sure, but if they're at/near 110/310, I should be fine.

 

[ntsqd]

That's a Spring PRESSURE concern. Mine is a Spring TRAVEL concern.

 

[bulletpruf]

That's a Spring PRESSURE concern. Mine is a Spring TRAVEL concern.

Gotcha. Looks like coil bind is .500 on these springs so I need to stay far enough under that to have a margin of error.

 

[ntsqd]

Why not buy the cam mfgr's recommended springs and after verifying that the valves have enough travel + some margin put them in the heads?

 

[bulletpruf]

Why not buy the cam mfgr's recommended springs and after verifying that the valves have enough travel + some margin put them in the heads?

It's more about the potential headaches than it is the $200 or so for springs, retainers, and locks. Like the heads I'm working on now; they need offset locks because the tip of the valve doesn't sit high enough above the retainer. Not too expensive, but still have to figure out the right part number, disassemble everything, reassemble, etc. Just so many things that you have to deal with - installed height, retainer to rocker clearance, retainer to seal clearance, seat pressure, open pressure, sourcing the right shims, do the springs fit the spring seat, do the springs fit the retainer, etc. If I keep the heads as-is, it can save a bunch of time.

It's also a temporary'ish engine, so it doesn't need to be optimized. I think on down the road, it will end up with a fuel injected 351W, but I'm not there yet.

 

[House]

I believe Sanderson still sells a set of headers that work with the P heads.

 

[McGirr455]

The steam holes from the early block don't match the P heads so on my friends build we put the late head gaskets on the early block and drilled the block to match. Just gets rid of the possibility of trapped air in the top of the block.

 

[fordguy]

Just remember the angled plugs. If it is temporar, find cheap explorer exhaust manifolds, they should work with most anything. I would prefer Gt40 heads versus p heads, but you already have them so go for it. I think you are on track. I understand the valve train dilemma , it cascades sometimes. My current engine was non stock and as things cascaded, just went back to stock (2000 explorer) valve train, except for replacement springs.

 

[Joshuasnr]

Just remember the angled plugs. If it is temporar, find cheap explorer exhaust manifolds, they should work with most anything. I would prefer Gt40 heads versus p heads, but you already have them so go for it. I think you are on track. I understand the valve train dilemma , it cascades sometimes. My current engine was non stock and as things cascaded, just went back to stock (2000 explorer) valve train, except for replacement springs.

You nailed it with the valve train dilemma, it absolutely cascades! Going back to the stock 2000 Explorer setup sounds like the smart move to stop the headache and just get the thing running reliably.

 

[bulletpruf]

The steam holes from the early block don't match the P heads so on my friends build we put the late head gaskets on the early block and drilled the block to match. Just gets rid of the possibility of trapped air in the top of the block.

Excellent tip. Wasn't aware of this issue. I found a pretty good thread on it here - https://www.vintage-mustang.com/thr...steam-holes-a-guide-and-walk-through.1147136/

Thanks!

Scott

 

[bulletpruf]

Just remember the angled plugs. If it is temporar, find cheap explorer exhaust manifolds, they should work with most anything. I would prefer Gt40 heads versus p heads, but you already have them so go for it. I think you are on track. I understand the valve train dilemma , it cascades sometimes. My current engine was non stock and as things cascaded, just went back to stock (2000 explorer) valve train, except for replacement springs.

Yeah, I was hoping for 3 bar heads, but the 4 bar heads showed up for $100 and I couldn't pass that up.

 

[Broncobowsher]

If you have stock Bronco manifolds they can be clearanced for P-head spark plugs. Cast iron manifolds carve nicely with a carbide burr. I ported a set of cast iron manifolds once. Not a bad job to do.

 

[bulletpruf]

If you have stock Bronco manifolds they can be clearanced for P-head spark plugs. Cast iron manifolds carve nicely with a carbide burr. I ported a set of cast iron manifolds once. Not a bad job to do.

Need to figure out what route to take here. I think I have one stock Bronco exhaust manifold (can't recall what happened to the other), and I also have some headers that likely will not work with the P heads. I do have a complete exhaust setup from manifolds to tailpipes that I picked up cheap. Guy installed it and it was too loud for him; has glasspacks.

 

[bigmuddy]

If you have stock Bronco manifolds they can be clearanced for P-head spark plugs. Cast iron manifolds carve nicely with a carbide burr. I ported a set of cast iron manifolds once. Not a bad job to do.

I have done the same as bowsher, I also added some heat protectant boots on the sparkplug wires and worked fine. Frankly, there were only a few wires that were getting toasty before adding the boots.

 

[bigmuddy]

Need to figure out what route to take here. I think I have one stock Bronco exhaust manifold (can't recall what happened to the other), and I also have some headers that likely will not work with the P heads. I do have a complete exhaust setup from manifolds to tailpipes that I picked up cheap. Guy installed it and it was too loud for him; has glasspacks.

I am sure you can round another manifold if wanted. Hell, I may have a set laying around.

 

[bulletpruf]

I am sure you can round another manifold if wanted. Hell, I may have a set laying around.

Are all early 302 manifolds the same or are they Bronco/F100 specific?