Joined: Wed May 2nd, 2018
Occupation: Elevator Design Worlds Tallest Buildings
Interests: Ranger Based Vehicles and OFFROAD
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|Quote from wiki:
"The Explorer/Mountaineer heads (GT40P) are somewhat smaller, measured between 58-61cc chamber volume. Thus, GT40P cylinder heads may give a small bump in compression. ... Both have 1.84" intake valves, but the GT40 has a 1.54" exhaust valve whilst the GT40P cylinder heads have a slightly smaller one at 1.46"."
Best description I have seen:
The GT40 & GT40P heads had a few differences that are note-worthy, the most importantly being the bump in compression. The GT40P heads had a small combustion chamber ranging from 58-61cc while the GT40 heads had a 63-66cc combustion chamber. The GT40 heads have thermactor holes built in to connect to the EGR/smog equipment whereas the GT40P heads us an external EGR connective system. The GT40P heads also had a different spark plug placement making header choice important. GT40P specific headers are needed unless you use spark plug wires with 90 degree boots to clear the heads.
They are both good performance factory heads, the gt40's are a little more sought after because they are considered easier to modify for performance, flow matching etc. The nonsense about shorty headers and interference with the spark plug angles is silly...I have personally bolted GT40p headers to GT40 heads and vise versa, the change in spark plug angle is easily over come with some 45 degree spark plug wire boots.
At the end of the day they are both good!!!!
Last edited on Thu Jan 30th, 2020 04:50 pm by 410customs
I build custom RBV, specializing in drivetrain conversions, wiring, suspension and complete custom trucks