Building GT40 Heads

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Building GT40 Heads

February 04, 2019, 06:29:14 PM

Hello, I am fairly new at engine building, and I have been considering buying some GT40 heads for my 5.0 bird, but I would like to know the best way to build them. What valves, pushrods, rocker arms, etc. should I use that would be proper for my bird? Would I re-use everything from the stock heads? And are roller rockers a good investment? I want to do a Mid-Output type conversion, maybe eventually a full HO conversion. Thanks!

Building GT40 Heads

Reply #1 – February 05, 2019, 05:49:19 PM

So you may be able to find a set of heads that you can reused everything and simply have the heads cleaned up and a good three angle valve job done and not blow a ton of cash. The only thing I would say is replace the stock valve springs and get new ones that will match the requirements of the cam to be used. See the TFS spring kit mentioned below.

If I was going to completely overhaul them this is the list:
Roller rockers - Definitely well worth the money and some of the more popular ones are Comp, Crane, Scorpion, etc. Depending on the cam lift, heads, valve or no valve reliefs on pistons, and piston position in the cylinder at TDC most run 1.6 ratio rockers. You will need to have the studs pulled from the GT40's and new studs (please just get ARP's and be done with it) will need to be installed which typically takes some machining and threading on each boss. Rocker arm length is another critical item so if you don't really know much about valve train geometry then you need to find a good machinist/engine builder to tell you what you will need. This will also go for the valves.
New valve springs - This will depend on what cam you run but I know a lot of guys run the TFS kit on pretty much an Ford letter cam and the TFS Stage 1 & 2 cams. TFS kit part number is TFS-2500100 and it comes with springs, retainers, and locks.
Valves - Manley Stainless Steel severe duty or similar and you will need to know stem diameter, length, and valve size. Again, machinist/engine builder will know what you need to order if you do not have experience or understand the geometry.

In either instance (rebuild or overhaul):
Push rods - you should use adjustable push rods and make sure a stock length push rod will work and if not order the correct length. Most folks do not understand how 0.1" will make a lot of difference.
Port work will get decent results with the stock valve train and better results with the upgraded parts in the overhaul. How much you want to do is up to you and understanding what to have done is important. A good head porter can walk you through the various levels and should be able to tell you what they would do with your planned approach. Examples are blending the bowls behind the valves, gasket matching the lower intake and heads to the gasket you choose to use, and as always working over the exhaust ports as they pretty much suck on all Ford production heads.

Remember that you can go over board on the heads and it will be better than stock but not as good as a matched setup with the rest of the motor. I put overkill on my heads knowing I was going to move up in cubic inches later down the road. Gave up a few horse power but now with the stroker motor it was nice not having to go back and spend more money as it was less money to do it the first time.

I am sure others will chime in on this as well. One thing I will tell you is that you can spend too much money on these heads in that at some point its just better money spent on a set of aftermarket aluminum heads.

Building GT40 Heads

Reply #2 – February 05, 2019, 07:46:16 PM

I used the TFS kit with my E cam and '40P's. It was what popped up the most when I was sleuthing for info, and Graham (88turbo) has the same setup and reports no issues.

I had a valve job done, used the stock valves. The machine shop guy said for a mild street 5.0 it would be fine. He's no longer with us now, but his work was and still is respected all over this area.

I'd have went with new valves had it been a total rebuild...lower mile block, so I left the bottom end alone, save for new oil pump. Good to go.

Interested in the numbers yours will make...god know's you've delt with some shiznit with this engine. Hope it's plenty strong for ya :)

Building GT40 Heads

Reply #3 – February 07, 2019, 02:07:53 PM

Basic bowl blend, 30* backcut on stock valves, install good seals and springs, unshroud valves/chamber work. Polish the whole chamber. Concentrate any porting efforts at slightly widening and smoothing short turn radius on intake ports. Dont raise exhaust port roof too high, you'll breach the water jacket, I've seen it happen, came close myself.

Labor for the bowl blending, chamber work, and valve backcut should run $200-300 all in. This will include disassemble, inspect, and reassemble. Any valvestrain parts, seals will be extra. Check their pricing first, compare, buy your own if they are not competitive.

Stainless valves are nice but overkill for these heads and at this power level. Ditto for 10* locks or lightweight retainers.

Use a quality 1.72 bolt down roller rocker, leave the stock cam in. These heads, even ported, the flow dies off at around .500 valve lift. Lifting the valve past that is power wasted compressing a valve spring for what amounts to non-existent flow gains/power gains.

Skip milling the heads for compression gains. More money wasted. Straightedge them yourself.

Run away from any head porter that talks about gasket matching before doing the above first.

Building GT40 Heads

Reply #4 – February 09, 2019, 06:42:27 PM

Thanks for all the help guys, you gave me a good idea of what I'd be dealing with. And I'm also finding out that with the price of gt40s that aluminum heads may be a better option. Will I have any clearance issues with aluminum heads? I also found these heads on ebay(the link bellow), and I was wondering if anyone has heard anything good about these heads.

https://www.ebay.com/itm/Ford-289-302-351W-408-427-5-0-Mustang-Aluminum-Heads-GT40-EFI-OR-carburetor/372038104093?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D7c4dc0abe1e14c6ebf9a16aef77793de%26pid%3D100675%26rk%3D1%26rkt%3D15%26mehot%3Dpp%26sd%3D372038104093%26itm%3D372038104093&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3Ae1992b9e-2cc2-11e9-86bf-74dbd180b9e7%7Cparentrq%3Ad49a5ebe1680a99b1d112a60ffba809b%7Ciid%3A1

Building GT40 Heads

Reply #5 – February 10, 2019, 02:13:21 AM

Pro Comp has a poor reputation for issues with valve guides and even casting porosity. I've never owned a set, don't plan on it.

I have owned AFR 185s, 205s, Edelbrock Performer RPMs, and TFS 170s and 190s. All have been very capable and trouble free heads for me. I've come across used Edelbrock and TFS heads fairly often for a good price, sometimes with roller rockers and ARP bolts included.

Clearances should always be verified since it is a simple procedure and not doing so can be costly and result in unnecessary downtime.

That said, assuming use of stock HO pistons that have a slight dish and valve reliefs, the clearance for heads using the 1.90 or 1.94 intake valves for many installs has been no issue at all. The 2.02 intake valve heads comes closer to contacting at the peripheral areas of the valve relief. The exception to this is the TFS Twisted Wedge heads which have a design that changes the valve angle in such a way that it results in better clearance for many stock piston applications.

Building GT40 Heads

Reply #6 – February 11, 2019, 08:19:01 PM

If you're set on GT40 heads, go for the earlier heads (3 bar) over the P heads (4 bar) the originals have a bigger exhaust valve, a more serviceable spark plug angle (not requiring specific headers) and no spring binding issues that I'm aware of. The P head has similar stock performance, but are a pain in the ass to go back to and work on later, not to mention the springs will bind. I used them over KB domed pistons and had to grind down the spark plug bosses in the chamber to avoid piston contact WITH THE HEAD. THE HEAD, not the valves. I regret using them.

Building GT40 Heads

Reply #7 – February 15, 2019, 12:06:55 PM

I thought you were talking aluminum GT40 heads as you never mentioned cast iron in your first post. If you have a choice then get the GT40X heads as they continue to flow up to about 0.650" of lift and when ported make some seriously good numbers down low and in the mid range. They respond to basic porting (clean up) and a good valve jot really well.

Here are the Ford installation instructions which provide the details on the heads and you will notice that the Y heads are small volume heads compared to the X's:

https://performanceparts.ford.com/download/instructionsheets/FordInstShtM-6049-X303X305Y303.pdf

A reputable porter should be able to clean them up and get the numbers up but not bad out of the box. If you have the money don't screw around with the stock cam. Call Comp Cams and work with them on selecting a cam for the motor or get a custom grind from Ed Curtis or Jay Allen. Lots of people think they understand cams enough to recommend cams or what to use but there are actually very few that truly understand the dynamics involved with valve trains. Anyhow, good luck and keep us posted.