GT40 Head problems

Hey guys, I just installed a set of GT40 (1993 cobra) heads on my 69 mustang and I have a mayor f*** up in my hands. I put new 3/8" diameter studs with comp cam guide plates, and proform 1.6 roller rockers. The problem is that it seems that the rocker bottoms out on the steam of the stud, right before touching the valve steam. It seems like a need only about 1/16" more travel. If I did not have the guide plates, I'm sure the set up would be fine, but I understand I cannot leave these out. What do you guys suggest. Is there someone else that have done this kind of mod on their vintage mustang? Also, what kind of spark plug do these head use? I bought a set of the original 302 sprk plugs and they are the wrong size.

Thanks for all your help guys and merry christmas.

I'm not an expert, but I believe your only options are either longer valves and shim up the springs, or have the rocker stud pads on the heads milled down a bit to allow for the extra thickness of the guide plates.
[addsig]

Longer pushrods may do the trick, just watch your geometry. If not motorhead's options are probably your best bet.
[addsig]

Thanks a lot guys...is there anybody that would like to take a shot at the spark plug that these heads use?

<font size=-1>[ This Message was edited by: labzerpa on 12/23/05 5:27am ]</font>

Autolite 764 is what we have in our GT-40's. Sounds like the stud bosses weren't cut right. If you just had tthe stock pedestal threaded, that's likely the problem. I had ours cut about .3 - took a pair of studs and a guide plate to the shop with the heads. He got it spot on - even the stock 302 pushrods set the geometry correct. BTW - the 302 is a 65 289 block with 70 innards.

_________________

1967 Falcon 4 door w/351C - Owner built, owner abused.
70 Mustang 302 / 02 Mustang V6 rag top, 04 SuperCrew parts hauler
http://raceabilene.com/kelly/hotrod

<font size=-1>[ This Message was edited by: ckelly on 12/23/05 10:20pm ]</font>

CKelly- You said you milled .3 off the stud boss- was that with .395 tip valves or the short .250 tip length? Back when I did my 289 heads I milled .3 off and it worked great with stock length pushrods and .250 tip valves. Just wondering because I'm about to do my GT-40 heads and I need to buy new valves, be nice to get it right the first time. Thanks.

I just drilled and tapped my heads, I didn't mill them down. I haven't had any geometry problems. What causes the problems, the length of the valve or the something cam related?

Don't know for sure what the figure was - that's what I pay the machinst for. Sorry. These are 93 stock GT-40 lightning heads, stock 93 valves. Came as Ford reman heads, milled by the previous owner to 61 cc but not installed. The only other mod was having them put on dual springs - and I let the shop pick the springs.



_________________

1967 Falcon 4 door w/351C - Owner built, owner abused.
70 Mustang 302 / 02 Mustang V6 rag top, 04 SuperCrew parts hauler
http://raceabilene.com/kelly/hotrod

<font size=-1>[ This Message was edited by: ckelly on 12/24/05 11:47am ]</font>

oldmustangjunkie, I believe the problem has to do with the guide plates. These rase the height of the stud by the thickness of the guide plate. That is why a good solution would be to mill down the stud buss the thickness of the guide plate to compensate for it. If you have a setup without guide plates or with standard studs you do ot see this problem. By the way, merry christmas to you'll and thanks for the help.