I just bought a pair of gt40p heads off an explorer and I was wondering if there is any modification needed To put them on my 85 fox? Also can I use the ford racing valve spring upgrade kit on those heads?
You definitely need to upgrade the valve springs on the P heads. Ford racing, trick flow, comp cams, Anderson ford motorsports all make upgraded springs for stock cast iron ford heads. I've got the trick flow 2500100 springs on mine. And are good up to a .540 lift. Check out latemodel restoration, American muscle, ford racing or any aftermarket parts suppliers and they'll have what ya need. And always check push rod length, and push rod to valve clearance whenever doing any upgrade.
I would look into the tfs spring kit. Also, most of the time, the p-specific headers will be needed, or the stock manifolds might work. It's the angled spark plugs that are the issues with the p heads.
alexs parts has drop in spring kits for those, and the price isnt bad either.
you might need different headers though depending on what you have.
bbk1515 headers ,90 lincoln "lincoln logs" will work. heat socks are suggested.