What is the difference between GT40 and GT40P heads? Also, what the heck are roller rockers and how are they different from whatever comes standard?
If you search Google, there is loads of info on GT40 Vs GT40P. More than any of us could ever type here.
Ok, new question, do the GT40P heads just bolt on? Or do I need something else? (I just had Hooker 6901s installed)
the problem gt40p heads is that the spark plug location and angle has been moved. they stick closer to streight out than at an angle that the stock plugs were at. this creates a clearance problem with the headers. there are some expensive things (cant rember the name) that allow the spark plug wires to clear the headers.
I have it on my car for 3 years now as long as you leave the plugs,engine alone there's no problems.. you'll need these spark arms things.
Basically aside from the spark plug difference, the GT40P heads also have slightly smaller exhaust valves and different porting too. There are two types of roller rockers, one has just a roller tip on the valve side, that really does little to improve the friction there as the contact point on the std rockers actually rolls across the valve tip when in motion. The other type (full rollers) have a roller trunion instead of a rocker fulcrum in the center (pivot point) this roller bearing trunion frees up a lot of friction vs a rocker fulcrum. When Ford decided to use full roller rockers on the 93 Cobra 5.0, they found a 15 hp increase over the stock stamped steel sled fulcrum rockers. Some of this was in the switch to the roller fulcrum and some wasin the increased rocker ratio (1.7 vs 1.6 ) which added .030 to the lift at the valve. Another benefit was the friction loss made the oil run cooler. I was sold on em after finding this stuff out. I wouldn't build a motor without em.
