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GT40/GT40P Heads and Ford Explorer intakes

GT40 and GT40P heads are probably the best factory production small block Ford heads.  GT40 and GT40P heads have line designations on the end of each casting.  3 lines on the GT-40 and four lines on the GT-40P.  GT40 heads are found on 96 and early 97 V8 Explorer/Mountaineers as well as 5.8L Lightnings and 93-95 Cobras.  GT-40P heads are found on the 97 and newer 5 liter Explorer/Mountaineer V8s. 

  • The GT40P replaced the standard GT40 on the V8 Explorers and Mountaineers in early 1997. Prior Explorers and Mountaineers had Cobra GT40 heads that were milled to bring it's larger combustion chamber down to the size of the E7 heads to keep compression up.

  • The 5.0 explorer intake was the same from 96-01.  These intakes are spin offs of the Cobra Intake.

  • The 5.0 explorer throttle body is 65mm and will fit a Mustang but you must swap out the throttle shaft and arm from the Mustang throttle body.
     

  • GT40 and GT40P share similar intake runner volumes at about 145cc compared to E7's 124cc.  All accessory bolt locations and valve train geometry are the same between the GT40P and GT40.
     

  • 1.85/1.46 valves compared to 1.85/1.54 for the standard GT-40. The GT40P exhaust port is redesigned and is more efficient than the standard GT40 which is the reason for the smaller exhaust valve. There is room for larger valves but keep in mind going larger on the intake side will cause clearance problems with the spark plug boss.
     

  • GT40P combustion chambers range from 59cc to 61cc based on factory machining tolerances.  GT40 combustion chambers are roughly  65cc.
     

  • Small emissions-type bump in exhaust port similar to E7TE casting but not as large. This bump is in the center on the port roof right at the exit and can be easily removed.
     

  • No thermactor holes in the GT40P heads
     

  • Intake port dimensions are close to a Felpro 1250 gasket.
     

  • GT40P can use stock pedestal mount rockers.
     

  • On GT40P heads the spark plug hole is moved down and rotated out which puts the electrode closer to the center of the combustion chamber. providing a better burn, reducing emissions and increasing efficiency.  The GT40P does not use standard 5.0L spark plugs.   GT40P uses Motorcraft AWSF-32C.
     

  • Standard unequal length shorty headers won't work because of the GT40P spark plug location. MAC offers a coated GT40P-specific shorty and Ford Racing offers a set of stainless shorties that work. Stock Mustang headers work also.  Most equal length shorties will not work. BBK equal length shorty headers have been known to fit. MAC, Hedman and BBK full length 1 5/8" headers fit.  Some full length headers require minor clearancing on some primary tubes but is not a big issue.  Spark plug wires with 90 degree boots are recommended with all headers.
     

  • TFS-2500100 valve spring upgrade kit comes with 1.47 springs, retainers, locks and valve seals.  A dual spring will NOT fit a GT40 head w/o machining to the inner part of the cup but a basic 1.46/1.47" single spring will fit, There is an inner "lip" that is about .060" tall that most likely will have to be machined flat.  You can also go a step further machine the guide too and use the 1.300" LSX dual springs.
     

  • Gasket matching does not net any significant increases in airflow on these heads. These heads are sensitive to the work in the bowl area (including the guide boss) and the short turn. A good 5 angle valve job is a good idea too.  If you are not a head porter, don't try to be one.  P heads are easy to screw up so leave the work to a professional.  If you want to get carried away, a 1.94 intake valve and 1.50 exhaust valve will help flow a bit.  Typical peak flow numbers on a well done set of P heads is about 230 cfm on the intake and 160 cfm on the exhaust at .500 lift.

  • GT40P heads are similar to GT-40 heads with the biggest difference being the P-heads feature a revised spark plug angle which extends the plug into the combustion chamber, putting the flame front close to the absolute center of the chamber, resulting in a smoother combustion process. P-heads have a smaller combustion chamber (approximately 59cc), which will increase the compression ratio over E7TE heads.

 

Head intake port combustion chamber intake valve exhaust valve
E7TE 124cc 61cc 1.78 1.46
GT40P 145cc 59cc 1.85 1.46
GT40-Explorer 145cc 65cc 1.85 1.54
GT40-Cobra 145cc 61cc 1.85 1.54

 

The following modifications must be made for Explorer intakes to bolt up to a 1987-1993 5.0 Mustangs:


1. Lower Intake:

  • The Explorer intake has no hole for the ACT (Air Charge Temperature) Sensor. You have two options here: Drill and tap a hole for the sensor or relocate the sensor.

    • NOTE: SN-95 Mustangs do not need to perform this modification as the ACT was located in the factory airbox anyway.

  • You'll have to swap over all related hardware from your stock intake (temp guage sender, coolant lines, etc)

  • The lower intake itself doesn't have a return port for the EGR coolant flow, so you have two options: Drill and tap for a return port or block off the supply port on the coolant lines.

    • NOTE:On vehicles using a Cobra upper or any upper that does not use engine coolant to cool the EGR spacer this modification is not necessary.

 

2. Upper Intake:

  • Swap the four throttle body studs from your stock intake onto the Explorer intake.

  • At the back of the stock intake, there are three vacuum ports (fuel pressure regulator, Emissions, and vacuum tree). At the back of the Explorer intake there are only two. You can use T or Y connector to split the ports.

  • Two of the other vacuum ports on the intake are a little too long, so using a cutoff wheel, trim them to the desired length.


 

Converting an Explorer 65mm Throttle Body for Use on Mustang:

The Explorer TPS is not the same as the Mustang. It uses a different resistance range and has the two bolt holes set slightly wider apart - you'll have to drill the stock Mustang bolt holes larger to get them over the 65mm TB mounting holes.

The tab at the end of the TB shaft that slips into the TPS is also a little too long for the stock TPS - it needs to be ground down to the same height as the stock tab.

The 65mm TB has the boss for the 90 hard line elbow line that runs from the oil fill neck to the stock TB but it is not drilled nor does it have the elbow. You cut the boss that the stock one is pressed into deep enough with a thin cut-off abrasive blade so you can crack the side of the boss away, making removal of the 90 elbow easier. Then use a uni-bit step drill with 1/4" long step sections to drill the new hole in the 65mm TB boss to accept the elbow. Then inserted it and use epoxy to hold it in place.

The throttle linkage ball is also "clocked" in the wrong position for the Mustang. Cut the linkage off an old 60mm TB and used it. The shaft is split at the end and when the factory slides the throttle bracket and return spring on it during assembly, they press the split end of the shaft and crush it onto the slot in the throttle bracket. Use a small abrasive wheel and grind the pressed halves of the shaft off so you can pry the throttle bracket off.  If you don't grind the stock bracket too bad and the slot is intact, it will slide over the Explorer pressed shaft halves and create an alignment that is correct. Epoxy or some spot welds can be used to hold the cut off 60mm bracket onto the 65mm bracket.