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GT500 heads

16K views 44 replies 8 participants last post by  4sdvenom 
#1 ·
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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#4 ·
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;
175616

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.

175617

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.
 
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#5 ·
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.
 
#6 ·
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
 
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#8 ·
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 ·
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!
 
#11 ·
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
 
#12 · (Edited)
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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#13 ·
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
 
#14 ·
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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#15 ·
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
 
#16 ·
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
I will look into this. I will probably end up doing it just to be safe due to the amount of boost I want to run. Any reccomendatins on valves? Like I said looking for something Inconel or better for exhaust.

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#22 ·
I have a local guy (https://www.facebook.com/Jandersonheads) that did a pretty great job on my heads. I think if you're not looking to spend $3000+, he would be a pretty good option for many. My heads are DB's that had some work done by a friend many years ago as well as larger Manley +1mm valves. He was able to make some large gains, especially on the exhaust side. I made 1346whp with these before he touched them and looking to make more once I get the engine back in in a couple weeks.

Intake - Before & After



Exhaust - Before & After

 
#23 · (Edited)
Those are very nice numbers Tony, especially if you consider the more attractive pricing your guy offers. The flow figures in the earlier post were "C" heads, a ported GT500 and two ported Coyote heads.

One of the nice things about the GT500 head, somewhere around 2012 or so Ford made a running change in the castings to improve strength for boosted applications. Those improvements make the heads last a bit longer under the sustained beating a race only engine gets.

Thanks for contributing.


Ed
 
#27 ·
I'm running a Sullivan lower now on 4.6 cobra heads. I had called to a couple shops a while ago about switching to gt500 heads and they said modifying the intake wasn't worth the hassle to run ported gt500 heads vs ported Cobra heads. Maybe that's true based on the data posted previously in this thread.
 
#28 ·
modifying the intake is the easiest part. The fact that used GT500 heads are $2K and used Cobra heads can be gotten for $300 is what kills most. The guys that have done GT500 heads that I know of have made far more power than ported cobra heads would be why I would do it.
 
#29 · (Edited)
What Josh said about the ported GT500 heads is true. I can not think of anyone who went to the GT500 head that did not make more power. You need to be circumspect when you do these sorts of evaluations because I also can not think of anyone who did not upgrade other aspects of the engine when they went to the GT500 Head so you will have difficulty doing an evenhanded A/B comparison.

What is absolutely certain however is that Ford made engineering changes to the basic GT500 head around 2012 or 2013 (don't remember which anymore) that substantially improved their strength especially when used in high power builds north of 1500 hp. The upshot was improved casting life at the elevated power levels and improved strength especially when using large head studs like the Accufab half inch studs with the 9/16 block side threads.

The very best ported GT500 heads have been reported to flow somewhere between 340 and some as high as 350 cfm. This might be significant at high boost levels but at lower boost levels - not so much. For example if we look at engine airflow in four different engines, one is n/a, one is 15 psi boost, one is 30 psi boost and one is 45 psi boost we see very different engine appetites for air. The numbers look like this;

Font Parallel Number Pattern Circle


Now lets say you have a head that flows 320 cfm (at 28" of H[SUB]2[/SUB]O) that works out to a flow capacity of 320 cfm per cylinder times 8 cylinders or 2560 cfm. To help put these numbers into perspective, a pressure drop (or delta pressure) of 28 inches of water across a port equates to 1 PSI pressure differential across the port being flowed. The chart above shows the n/a engine's air flow appetite as 591 cfm at 8500 rpm. A cylinder head that is capable of 320 cfm at a delta pressure of 1 psi through a single port will have a more than adequate flow capacity for a naturally aspirated engine that only requires 591 cfm for the entire engine at 8500 rpm.

Yes you say but that is n/a. Well, when you go up scale and run higher boost pressures you get a scaled representation of the same phenomena. The heads again far exceed the engine's appetite for air. When you change the pressure drop across the port (boost) to 15 / 30 / or 40 psi from 1 psi, you are magnifying the port flow capacity by a country mile and you are back to the obvious question, why am I doing this and what was it that I was worried about again?

Net, net bottom line, in real world flow considerations the performance difference between two heads that are separated by 10 or even 20 cfm at the mid 300 cfm flow range will turn out to be negligible, if measurable at all, in engine performance. The associated changes that most engine builders make when they go to the marginally higher flowing head are typically the contributors to the increased power they observe and report.

That said, if you were going to build a race only or predominately race only engine at high boost the last generation of GT500 head is by far the most robust casting Ford has offered and worth the investment just from a parts longevity perspective - if you consistently race the engine at boost levels above 30 psi. If you are like most of us and usually operate well below 20 psi with the occasional foray into the 30+ psi boost range then a well ported "C" head is what you should be looking for. The monies saved will easily find other pieces to buy for the build.

When you are attempting to select a porting service pay attention to their mid and low lift flow performances. A robust flow performance from 0.200" lift through 0.400" translates into significant horsepower because of increased cylinder filling efficiency. Your valve is only at max lift once. It is at mid lift twice! Once during the opening ramp motion and once during the closing ramp motion. This is substantially more time than you will be spending at max lift. It is also where the bulk of the cylinder filling occurs.

The second place in your lift / flow map you want to pay attention to is the no-mans land between zero lift and 0.100" lift. The long duration camshaft opening and closing events are designed to take advantage of this cylinder filling opportunity just after the valve opens and just before the valve closes to both enhance the initial filling event and also cram that last bit of fuel air charge into the cylinder at the end of the closing event. If your ported heads under perform in this region you are basically chopping off "X" number of degrees of valve open duration - which begs the question, why did you buy that nasty longer duration, bad mannered cam?

Porting shops have had the ability to get much better at what they do in terms of port development with the advent of CNC port development tools. The best example if this is the Coyote heads. Both their intake and exhaust valves are substantially shorter than a corresponding Modmotor head yet the casting flows as well as the better ported modmotor heads. Why? Flow dynamics and port development learned over the last 15 to 20 years of CNC port development.

In general you will be well served by buying a ported "C" head done by a shop that produces robust low and mid lift performance - that's where the gold is buried. If you miss the max lift flow of your favorite internet killer head, in the big picture it is all but irrelevant. Go for the gold. You will find it is buried in the low lift and mid lift flow numbers.

Ed
 
#30 ·
I appreciate the detailed response. I see your point with low to mid lift flow numbers.

One thing that you haven't mentioned that I'm curious about is exhaust flow of the head versus intake flow. To my untrained mind, the flow on the exhaust would potentially be more important than intake because the intake is pressurized and the exhaust wouldn't be.

My car is a turbo setup so I'm sure that changes the dynamics versus a supercharged car.

Comparing flow numbers with two companies livernois and fox lake. Fox lake claims to flow a lot better on the exhaust side but not the same on the intake and livernois does better on the intake not so much on the exhaust.
 
#31 ·
Exhaust pressures historically have run much higher than intake pressures especially at initial blow down when the exhaust valve opens. That said the engine power output is simply the total amount of fuel and air that can be burnt per operating cycle. You want to optimize the intake and especially on a turbo application you have little you can do to change what happens after the exhaust valve opens.

Newer design turbos can produce impressive boost (and therefore power) figures at lower exhaust pressures than their older siblings. These turbos may or may not spool as quickly as some of their higher pressure hot side cousins. You need to spend time with your Turbo supplier to optimize that metric for your build. That said you'll notice that rules making bodies focus on inlet side performance (boost) when attempting to normalize performance between cars with different types of superchargers. They don't do the same for the hot side design metrics — there is a reason. You've got to keep you eye on the ball and not be distracted by side shows. Other than keeping the hot side plumbing as short and hot (at the turbine) as possible along with minimizing unnecessary bends in the tubing your horsepower is intimately associated with the compressor side of the device.

There is an argument that can be made that restrictive exhaust plumbing creates pumping losses that are paid for with horsepower that never gets to the rear tires but the real world numbers argue that the low hanging fruit, power production-wise, is on the inlet/compressor side.

Don't try to over-science this process, you'll be much happier.


Ed
 
#33 ·
Don't forget the low off the seat lift is equally important to the cylinder's filling efficiency. The Livernois flow numbers are a poster child for the low lift and also the 0.200 to 0.400 lift range. You are unlikely to find any "C" head measurably outperform them in this range and when you look at the graph in post #4 the trace that sits clearly aboven anyone else is the Livernois Stg 3 head.


Ed
 
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