Local machine shop claims they need to install new valve seats to deal with un-lead fuel.GT40/GT40P heads are from un-lead fuel era, not quite sure of this advise. Question reguarding cyl head milling GT40 & GT40P to change cc?? Example each .010removed = aprox cc. Lost my past info and can not seem to ask search the correct ?? Thanks in advance JMDMT

 

Both heads have induction hardened seats, what this means is Ford heats the parent metal in the seat area, then quenches it to harden only that area. This treatment will hold up as long as needed until too much material is removed in regrinding the seat area. Normally, this is good for the first valve job after they're new. A second job may need new seats installed. On E7 heads (these have a similar chamber volume) each .010 removed equals a little under 2 ccs, a .040 cut reduces the chambers by about 6 ccs.

 

baddad457 are you saying for example if the heads have not been ground , just installed new that there most likely one valve job in them before they need seats? If you don't get carried away. Thanks for the info.JMDMT

 

That's good because it's wrong, the iron GT40 heads didn't exist until 1993 and the P version until 1997. As for shaving them to increase compression you want to be careful, Gt40s often had the same size chamber as E7 at 64cc give or take a couple points, but P's were often 58-61cc to begin with so you need to research the casting numbers and measure the chambers before you start shaving them down even further.

P.S. There were several different heads used on Ford and Shelby competition motors in the '60 including the original GT40 LeMans car and as a result some of these were referred to as "GT40" heads but they weren't actually cast as such like the late model GT40 heads pictured below which I'm pretty sure is what you're buying. Casting numbers for modern GT40 heads are F1ZE, F3ZE, F4ZE, F7ZE while the older heads that used to be referred to as GT40 heads are actually heavily modified HiPo 289 castings with casting numbers that start with a C like C6FE.

 

Yes, that's what I meant. And also be advised that the GT40 heads used on the Cobra Mustangs were milled a couple of extra passes to reduce their chambers to a nominal 60 cc's. According to Ford, you can mill up to .040 from small block Ford heads before running into intake fitment issues, this info excludes the Cobra GT40 heads because they were milled more from the get go.