GT40P heads and 289 engine question

pazcarguy

New Member
Mar 30, 2005
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Pittsburgh, PA
I have an opportunity to purchase some new GT40P heads for a 1966 289 that I am building. The block has been decked and has new flattop pistons for a CR of just under 9.5~1 with 60 cc heads. I was told (haven't been able to verify) that the GT40P heads won't work on an early 289 beacuse they are set up for a roller motor. I thought this didn't matter as I am using a flat tappet cam. Is their anything I am missing? I was planning on using 1.6 roller rockers and didn't know waht pushrod to use. I am going to use the Edelbrock Performer RPM cam (#7122)(.520 lift). I didn't know if the stock GT40P valve springs were suitable for this if I can indeed use the head. Anybody out there do this before? Brian
 
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Im not sure why they wouldnt work, but the stock valve springs will not hold up to .520 lift. I dont have specs, but my guess is a stock cam with 1.7 Cobra rockers (.478 lift) is only reliable to 5,000, maybe 5500 if you want to push it.
 
You might need to upgrade the springs for that cam. Try doing a search and compare the spring specs first. The Explorer cam's specs are 256/266 advertised duration, .422/.445 lift with 1.6 rockers. No change in springs needed for this cam with 1.7 rockers. (lift increases to .445/.473 with 1.7's) Most stock Ford springs are OK with up to about .530 lift. The spring rates are what would concern you most. You may also need to match up the coolant ports between the heads and block too.
 
I have that same cam in my 68. It was a night mare. You need the Edelbrock springs, and will have to check for proper push rod length. I didn't have the right springs at first, and didn't measure for push rods, so now I'm on my 2nd cam, third set of push rods, and 2nd set of roller rockers as well.....