Michael Johnson
Technical Editor
December 12, 2000

Step By Step

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138_00z Ford_mustang Left_front_view138_09z Ford_mustang Engine_view
1. Before you get started, drain the coolant and then remove your mass air meter and air intake hose. Then remove the upper intake and valve covers. Don't forget to disconnect the 10-pin connectors at the back of the upper intake.
138_10z Ford_mustang Fuel_line_removal
2. Use a quick-disconnect tool to loosen the fuel lines from the fuel rail. A little fuel will pour from the lines when you disconnect them, so soak it up with a shop rag to eliminate the chance of fire.
138_11z Ford_mustang Fuel_line_removal
3. Holten has a fuel pressure gauge on his GT. He removed the line from the gauge before taking off the lower intake. This would be a good time to remove the accessories from the engine as well, such as the A/C compressor and the alternator.
138_12z Ford_mustang Engine_view
4. With all fuel lines and electrical connections loosened, remove the lower intake. Don't forget to loosen the cool-ant hoses that are attached to the metal lines on the lower intake.
138_13z Ford_mustang Rocker_removal
5. Next, remove the rockers. In Holten's case, he was running stud-mount Crane 1.6 ratio roller rockers. For the GT-40P heads we used Crane's 1.6:1 pedestal-mount rockers.
138_14z Ford_mustang Cylinder_head
6. Remove the pushrods, then loosen the head bolts. Holten's car has ARP studs in place of factory bolts.
138_15z Ford_mustang Engine_view
7. Once the heads have been removed, the cleaning process can begin. Using a cleaning pad, such as a Scotch Brite pad, and judicious amounts of brake cleaner will have everything clean in no time. The block must also be clean before installing the new heads.
138_16z Ford_mustang Cylinder_heads
8. These are the Explorer, or GT-40P, heads we installed. They're available from Central Coast Mustang in either stock or modified form. Ours received the Trophy Stock-legal treatment, which means port-matching. The lower intake on Holten's GT is ported, and the heads were port-matched to the intake. Notice the combustion chamber layout with the spark plug located toward the center of the chamber.
138_17z Ford_mustang Cylinder_head_install
9. Using the studs as guides, Holten lowered the heads into place on top of Fel-Pro head gaskets. Holten also painted the heads the same color as his block and valve covers to make everything look like it was designed to be there.
138_18z Ford_mustang Engine_view
10. Torque the heads down to 70 lb-ft for the top bolts and 70 lb-ft for the bottom bolts. The upper bolts receive more clamping force to offset the wedging effect of the intake when it's bolted on.
138_19z Ford_mustang Roller_rockers
11. We're using Crane Cams Gold Race 1.6 ratio roller rockers. These are pedestal-mount rockers, which the GT-40P heads require.
138_20z Ford_mustang Roller_rocker_install
12. To properly install the roller rockers, rotate the engine until the lifter is on the heel of the cam. While you're tightening the rocker, rotate the pushrod with your fingers. When you can't rotate it any further, the rocker is at zero lash. Then tighten the adjusting nut one-quarter to three-quarters turn. If you must turn the adjusting nut more than that, you must use the supplied shims to properly adjust the rockers. In our case Holten had to use the shims.
138_21z Ford_mustang Headers
13. MAC produces the only header made for the GT-40P heads. They were easy to install and Holten liked them better than the equal-length headers he was using. One thing we really liked about the headers was that they actually had studs in the collectors and were not just loosely fitted with nuts and bolts, which eases installation.
138_22z Ford_mustang Header_gasket
14. Now that the heads, valve covers, and headers are installed, Holten loosely attached the two end bolts for the headers and slid the header gaskets into place. We, again, used Fel-Pro gaskets.
138_23z Ford_mustang Intake_gasket
15. Holten likes to use RTV instead of the supplied cork front and rear intake gaskets. He applied a liberal bead of RTV and allowed to set up while working on the side intake gaskets.
138_25z Ford_mustang Engine_view
17. Next Holten reinstalled the lower intake, being careful not to pinch any wires or connectors and using two studs to guide the intake into place. Don't forget to attach the two coolant hoses to the metal tubes on the intake.
138_26z Ford_mustang Engine_view
18. Holten torqued the intake bolts to 20 lb-ft, working from the center bolts out. Be sure to go back and retorque the center bolts. Now you can connect the fuel lines and the coolant hoses from the water pump. If you have a fuel pressure gauge, attach the line at this time.
138_27z Ford_mustang Distributor_view
19. Rotate the engine to top dead center and reinstall the distributor. Make sure the rotor button is pointing toward the back screw right below the button. Usually this will put you at the point where you can easily adjust the timing.
138_28z Ford_mustang Engine_view
20. Reinstall the accessories before installing the upper intake. You'll notice how Holten has his A/C compressor blocked off. If your air is in good working order you must first have the Freon evacuated from the system. When you're done, have the system recharged.
138_29z Ford_mustang Engine_view
21. The upper intake is then reinstalled. It's starting to look like an engine again! Be sure to also attach the 10-pin connectors at the back of the intake.
138_30z Ford_mustang Throttle_body
22. Attach the throttle cable bracket and pop the cable back on to the throttle body. Attach all other electrical connections as well, like the throttle position sensor.
138_31z Ford_mustang Engine_view
23. Wow, that went surprisingly well. All told, the installation only took about eight hours from start to finish. Holten didn't want us to give away his air induction secret, but we really didn't think it was that great anyway.
138_32z Ford_mustang Engine_view
24. Always change the oil when you take an engine apart like we did here. We used Synergyn synthetic oil for this article. This synthetic blend is made for high-performance vehicles and will surely go a long way in making sure Holten won't blow the thing up anytime soon (we hope).
138_33z Ford_mustang_hatchback Right_front_view
25. Jamie Holten's best time before the swap was a 12.63 at 105 mph. After installing the GT-40P heads, that time dropped to a 12.46 at 107 mph. 5.0

We guarantee plenty of burnout action when you add GT-40P heads to your 5.0 Mustang.

For real performance, stock E7TE heads leave a lot to be desired. However, stepping up in the performance head market will set you back more than $1,200 for a decent pair of aluminum castings--and that's straight out of the box, with no porting. A good port job can set you back another $500-$1,000. After a couple grand you have a killer set of heads, but there's got to be a less-expensive way of making horsepower. Sure, you could race-port the existing E7 castings, which many have done, but then you're putting quite a bit of change into stock heads. There is a better way. Central Coast Mustang sells GT-40P heads at a great price, making them a viable alternative in a market flooded with performance head choices.

Commonly referred to as Explorer heads, GT-40P iron castings are found on current 5.0-equipped Explorers. Similar to regular GT-40 heads, the biggest difference between the two is that 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 at 59cc, which will bump the compression ratio up on an otherwise-stock 5.0 engine. Because of this, your tuneup will probably need to be modified. With the GT-40P heads you will need to back off the timing a couple degrees and bump up the fuel pressure. Obviously, tuneups will vary. You just want to keep it out of detonation.

While we've seen engine dyno tests performed with GT-40P heads replacing factory E7TE castings and resulting in a boost of more than 25 hp, we have reluctantly set our horsepower gain goal at 25 ponies, as well. The reason for this is that we're actually replacing mildly worked E7TE heads. For this reason, we're not sure what kind of boost the GT-40P heads will give. Dennis Hilliard of Central Coast says we can expect to gain three-tenths in the quarter-mile. This kind of improvement may not seem like much, but the owner of our test car, Jamie Holten, runs in FFW Trophy Stock where three-tenths is a lifetime. Holten's best time is a 12.63 at 105.9 mph, and if we gain the desired result he will be right in the thick of things in Trophy Stock competition.

Along with the heads, we used MAC headers for GT-40P heads. MAC is the only manufacturer of these headers, and the parts we installed fit like a glove with no problems whatsoever. With the P-heads requiring pedestal-mount rockers, we also called up Crane Cams for a set of 1.6 pedestal-mount roller rockers. If you're running a stock cam, 1.7 rockers will work perfectly. However, since Holten's car has an E303 cam, we didn't want the pistons and valves becoming too close, so we chose the 1.6 rockers. As with all head installations, check piston-to-valve clearance before final startup.

We did the installation at Holten's place of employment, Motorworks, in Longwood, Florida. It took him and yours truly eight hours from start to finish, using air tools and a lift to gain access to the header flanges. We turned to Rare Auto Design in Orlando for dyno tests to find out how much horsepower we gained. A trip to Orlando Speed World provided us with updated quarter-mile times.

Boy, were we surprised with the results. We gained 45 hp and 40 lb-ft of torque. At the dragstrip, we gained two-tenths and 2 mph. We know what you're thinking--only two-tenths from an extra 45 hp? Let us explain. Holten runs the factory fan, but he had removed it when he ran the 12.63. However, when we dyno'd the car before installing the GT-40P heads, the fan was on the car. Holten tells us removing the fan is worth two-tenths in itself, which tells us the fan soaks up roughly 20 hp. After we installed the heads and with the fan off, he ran a 12.46 at 107.9. We then dyno'd the car without the fan to get some consistency and were rewarded with a peak of 316 hp at 5,500 rpm, and 348 lb-ft of torque at 4,000 rpm. If we subtract the 20 hp that the fan is worth, we end up with a gain of 25 hp.

Now we know why Dennis Hilliard of Central Coast Mustang is so high on these heads. With no other changes we gained 25 hp using factory iron heads. Through Central Coast you can have the heads fully prepped for your combination. As a matter of fact, Central Coast has an '89 coupe with GT-40P heads that has run a best of 11.98 in the quarter-mile.

All in all, the addition of GT-40P heads to any 5.0 Mustang is a worthwhile venture, especially if you're on a budget (aren't we all) or shooting for the Trophy Stock title.

Horse Sense:
The smaller valves found in GT-40P heads improve airflow velocity.