GT500 heads

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Thread: GT500 heads

  1. #1

    Default GT500 heads

    I was wondering, due to the GT500 heads having the best flow characteristics, can these be bolted to a 4.6 block with no issues? Ive heard a few times they can be and are frequently, but just wanted to get a definitive answer.

    Thanks!

    Robert

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  3. #2

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    They bolt up but require a special manifold, Robert.

    Ed

  4. #3

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    Quote Originally Posted by eschaider View Post
    They bolt up but require a special manifold, Robert.

    Ed
    Thank you Ed. I will stick with DC 4v heads then.

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  6. #4

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    Robert,

    Something to think about in the heads department;

    The GT500 style casting has a smaller lash adjuster used for the intake which allows a a taller straighter port with a better short side radius and improved flow. The typical "C" head while using the same valve does not have the same port geometry. The port is slightly lower and the short side radius is not as gentle as the GT500 head.

    That said, the valve length on either the Cobra style "C" head or the GT500 style casting are both the same. Manley lists the valve length as 5.339" for the intake and 4.587" for the exhaust. By comparison Manley lists the newer Coyote heads intake valves at 4.722" and the exhaust valves at 4.274".

    The longer the valve, the straighter the possible port geometry and the more gentle the all important flow limiting/enhancing short side port radius. The shorter valve used in the Coyote head speaks to a less attractive short side radius in the intake ports. So how do they flow more air? The Coyote head uses a small lash adjuster just like the GT500 heads but it has a substantially shorter valve. The intake port flow was the benefactor of more than a decade of port development work before the Coyote head ever saw the light of day.

    If you do similar work on the "C" head or the GT500 casting you would get similar results. You need to remember the ultimate flow of any head is determined by the size of the head of the valve, the old bigger is better story. The actual head flow is that ultimate flow associated with the valve head diameter diminished by the quality of the port geometry behind the valve. Ford went out of their way to clean up the as cast ports on the Coyote's and even began to offer the head with CNC enhanced ports.

    Like most racing disciplines the head porting shops improved their game over time learning from each other, Detroit efforts like the Coyote and just hard fought R&D work in the science of port flow dynamics. Here are some comparative port flows that infrequently find their way to the same page;

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    None of these heads are stock heads, all heads have been ported. Interestingly after porting, the heads look quite similar in terms of flow numbers. Just looking at numbers can be deceiving however. If you graph the flow figures some other data becomes apparent.

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    The first thing that jumps out at the viewer is the fact that all the heads essentially flatline after 0.500" lift. There might be bragging rights (as luck turns out there isn't) up there but there is no significant increase in flow up there. More to the point the commercially available Modmotor valve springs have a maximum useable lift of 0.550" which means a 0.600' lift cam would coil bind the valve spring.

    The second thing that jumps out is that one head's flow numbers stand tall above all others across the entire lift range. That head is the Livernois Stg 3 head. Actually this is not surprising when you start to dig into the specs. That Livernois head uses the 1mm larger valves and seats to produce the flow numbers. The other heads are all quite similar and all flow limited by valve diameter.

    Bottom line save your money on a lot of the other stuff. Pony up the bucks to have Livernois do their Stg 3 job on your C" heads and revel in the knowledge you're the biggest, baddest dog in the junk yard.

    Special point, Livernois today likes to use a 0.5 mm oversize valve so they don't have to do seats and a new valve job. Bite the bullet buy the new seats (the exhausts ought to be replaced anyhow) and get the best flowing heads for your project. Don't forget the most hp is derived at the highest engine speeds — think Mihovitz engine speeds ...


    Ed

    p.s. There is one significant benefit to a GT500 head not a GT500 style but an actual GT500 head. Ford beefed up the castings on these heads to better withstand the abuse they see in a s/c environment. So while they don't flow significantly differently they should (might) last longer.
    Last edited by eschaider; 06-23-2019 at 01:02 PM. Reason: Added Postscript

  7. #5

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    Thank you Ed! Great to look at the numbers. I will stick with the C heads seeing as I can net similar results for a much lower cost and they will continue to work with my stock lower manifold. Livernois was who I was looking at for porting, so hearing you recommend them is a big plus. I have a line on someone selling a very low mileage set of DC heads so I will snatch those up and go from them. Getting excited as I am slowly getting closer to have all the parts I need to start assembling my motor.

  8. #6

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    Glad it was helpful, Robert.

    Something to keep in mind with the Livernois porting service. At different times over the years Livernois has had quality control problems in terms of returning the same heads with the same cam caps to the same owners. Once you get them mixed up and worse send them to different customers in different parts of the country it is all but impossible to put Humpty Dumpty back together again.

    My recommendation, when you send in your heads, is to mark the castings so you know if you are getting the same castings back and keep the cam caps, do not send them to Livernois — they are not necessary to port the heads. I don't know how Livernois has sorted out the mixups in the past but I wouldn't be surprised to find out they provided replacements that were not the same head the customer sent in. When you keep the cam caps mark them as left head and right head so you can put them back on the correct head.

    Prior to sending your heads you might want to have a discussion with the Livernois folks and assure yourself that they understand the castings you send in are the castings you want back — especially if you are sending something like DC castings. You definitely want your primo castings back. Find a spot to put your name or other identifying mark on the outside of the casting. Names are much better than numbers. Take a pic of the head with the name inscription. Send a copy of the pic in with the heads and impress upon Livernois you want your heads back not someone else's.

    Because eveyone's focus these days is Coyote components, Livernois will most likely have a lot of Coyote work and not much Modmotor work. That plays to your advantage. Be diligent, be cautious and be deliberate. Their porting is stunningly good. Their ability to match heads up with their original owners and cam caps up with their original heads has fallen short of the mark more than once over the years.


    Ed

  9. #7

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    Ed, I will keep that in mind. I have heard horror stories of other shops doing similar things. Might be time to buy a numbering punch set and have some fun!

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  10. #8

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    The electric pencils that use a fine point tip to inscribe the characters you are writing is a better approach. If you happen to pick a thin spot on the casting it will not break through.

    Ed

  11. #9

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    Quote Originally Posted by eschaider View Post
    The electric pencils that use a fine point tip to inscribe the characters you are writing is a better approach. If you happen to pick a thin spot on the casting it will not break through.

    Ed
    10-4 I think I have one lying around somewhere

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  12. #10

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    Does anyone know the maximum over-sized intake and exhaust valve size C heads can take? Is it +1mm intake +2mm exhaust? Still doing research for once I get these heads ready to go to the machine shop. Want to make sure I have everything exact before getting everything done!

  13. #11

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    The largest commercially available (off the shelf and over the counter) valves are +1mm and a good valve at a reasonable price is the Manley +1mm valves you can get a Jegs or Summit.

    It would be difficult (read expensive but not impossible) to go larger. The challenge you would run into, cost not withstanding, is the shrouding from the close proximity to the cylinder wall. There are cute little tricks that have been used over the years to mitigate the shrouding like cutting complementary reliefs in the top of the cylinder. If you are running replaceable flanged sleeves this is possible. If you are running the OEM cast in place liners I would strongly discourage you from this sort of modification.

    The overall best head flow performance for the 4.6L "C" heads was the Livernois port job and a set of 1mm oversize Manley intake and exhaust valves along with 1mm oversize valve seats.

    The monies you would spend to go above those valve sizes would bring tears to your eyes and no appreciable additional power to the table. Don't forget those 1mm oversized Livernois ported heads outflowed all other heads everywhere on the lift curve. Although I didn't plot the curves, the Livernois port also outflowed two different generations of Roush Yates NASCAR heads out through 0.450" lift or so. Don't micro manage a winning package. Doing that will put you on the outside looking in.


    Ed

  14. #12

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    Thanks ed. Definitely do not need to go as far as scalloping the liner as much as I'd like to go balls to the wall insane. Probably would be suited better for a NA application anyways. I'm looking at doing Inconel exhaust valves and stainless intake with a ceramic coating in the chamber. I'm looking at building a set of heads which can take long periods of full throttle acceleration for things like the Texas mile or land speed racing. Any reccomendations for building a set of heads for useage situations like this? Obviously livernois porting is a must.

    Also, I recently got a 99 cobra long block with a set of good heads on them for cheap. Is there any benefit besides cooling to running a newer revision of the C heads?

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    Last edited by rainyp71; 07-19-2019 at 12:25 PM. Reason: Added info

  15. #13

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    As far as the newer revision heads go. The DB and the DC castings both have 9 thread spark plugs. The DC being the latest and greatest and last revision of the C heads. All other castings only have 4 thread spark plugs to them. For what you’re doing I would definitely look for a DB or DC castings with the 9 threads or at least have the 4 thread castings lock-n-stitched with a higher thread count insert. Ed can correct me if I’m wrong but I believe you want to avoid the Heli-coil brand because I believe the insert is steel and can create hotspots that will promote detonation. I believe the lock-n-stitch uses an aluminum insert.
    Like I said. Ed can correct me if I have that wrong.

    Ken

  16. #14

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    Quote Originally Posted by 4sdvenom View Post
    As far as the newer revision heads go. The DB and the DC castings both have 9 thread spark plugs. The DC being the latest and greatest and last revision of the C heads. All other castings only have 4 thread spark plugs to them. For what you’re doing I would definitely look for a DB or DC castings with the 9 threads or at least have the 4 thread castings lock-n-stitched with a higher thread count insert. Ed can correct me if I’m wrong but I believe you want to avoid the Heli-coil brand because I believe the insert is steel and can create hotspots that will promote detonation. I believe the lock-n-stitch uses an aluminum insert.
    Like I said. Ed can correct me if I have that wrong.

    Ken
    Thank you ken, I completely forgot about the 4 vs 9 thread delimma. I think I will just attempt to sell these heads. If anyone wants a set let me know, I'll let go of them for cheap.

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  17. #15

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    Ken is spot on in his explanation, Robert.

    That said you should not shy away from the Lock-N-Stitch repair for the head(s). The finished head is actually stronger in the plug thread area than a new 9 thread casting. You sort of get a hint at the strength when Lock-N-Stitch tells you the torque spec for the plugs is 35 ft/lbs after a Lock-N-Stitch repair!

    With a taper seat plug like we use you don't need to go that high. A simple spin down of the plug and a light snugging from your wrist is all that is needed to properly seat the plug.

    BTW just incase yo have not heard of Lock-N-Stitch they are the Ford recommended repair solution for the heads. If that endorsement isn't strong enough for you, they are also the contractor that was selected to stitch up the cracks in the cast iron Capitol dome in Washington DC. A major portion of their business is stitching together cracked metal components without welding! All things considered, pretty whizzy guys ...


    Ed

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