Got Myself A Gt Need Advice

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by justinb2488, Jun 4, 2013.


  1. justinb2488

    justinb2488 New Member

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    OK so I got a 1991 gt 5.0 from a buddy of mine pretty cheap. First thing I hear to do is get the gt40 heads off explorers. Then I heard that headers won't fit around them. So first thing is should I bother to get these heads. I'm kind of on a budget so might be my option if I can find headers that will work with it. Second I want to do cam and lifter upgrade. This is my second car so its gonna be my weekend driver so I'm not worried about tearing it apart. So if I got the gt40p heads how big of a lift off the cam can I get. So just need some info on that and also what else I should consider doing. Also heard about getting under drive pulleys also.
  2. davis3

    davis3 Active Member

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    Welcome!

    There will be no issues if you use the GT40 heads found on the earlier 5.0 explorers.

    You will need different headers if you go with the GT40P heads found on the later 5.0 explorers, due to the different spark plug angle found on the "P" heads.
  3. justinb2488

    justinb2488 New Member

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    So is there different gt40 heads I can find on other vehicles that have gt40 heads that are more easier with headers.
  4. stykthyn

    stykthyn Commander of the snuggie cultists

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    ahh the old mod bug. If I were you I would just get the entire explorer/mountaineer longblock and swap in a new cam. move all your fox related accessories over and call it a day. if you use frpp headers they will work with the p heads and the stock as well. good luck. let us know how it goes.
  5. justinb2488

    justinb2488 New Member

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    Is the frpp headers long tube?
  6. 88LX5.Oh

    88LX5.Oh Advanced Member

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    No valve springs in stock GT40 (or even P heads) are good enough for the stock Mustang cam. Unless you like valve float. You'll need different valve springs no matter which way you go. I want to say that the Trickflow spring kit is very commonly used in the GT40 series heads. I think prior to '98, the Explorer/Mountaineers had the GT40 heads. '98 to '01 had GT40P heads IIRC. FRPP headers work perfect with them, OR you can use 90 degree spark plug boots and do just a little bit of prying on cylinders 4 and 5's primary tubes on a different set of headers. That's what I did with my Bronco and it worked out good.
  7. 88LX5.Oh

    88LX5.Oh Advanced Member

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    Shorties but long tubes can work with P heads.
    My dad has Flowtech equal length long tubes on his drag car and all he did was put 90 degree spark plug wires and it worked out good for him
  8. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Far too many people put a dab of this and a dollop of that, and then wonder why the car doesn't run worth beans. Then they think off the shelf computer chips will fix their mismatched parts problem. It won't You have to have a plan for what kind of performance you want: Hot street. Street/Strip, Pure strip, Autocross or Road course. Each one requires a different strategy and a different set of components.. Mismatch the components and you’ll have a car that falls flat on its face when you demand performance.

    Everyone thinks HP! HP! HP! and thinks that peak HP is what they need. Peak HP is great for a drag strip car when it has the proper gears and tires to get the car up into the high RPM range where it develops that high peak HP near the finish line. On a street car, that strategy will have Honda Accords outrunning you, because you will never get the engine RPMs high enough without running over everything in your path.

    Here’ the strategy: Always remember that there are some tradeoffs in any engine combination. Most of us don’t have enough money to “have it all” as if it was possible by some masterful combination of parts and tuning.
    The following recommendations are for 5 Speed Manual transmission cars without NO2 or pressurized induction, stock short block.

    1.) Hot street: Broad flat torque curve, high velocity airflow in the intake and heads for best throttle response. Gears suitable for reasonable gas mileage and long road trips without excessive engine RPMs. Stand on the gas pedal from a rolling start to squeeze into that gap in traffic in front of you, and it jumps quick and hard to get you there. Max RPM’s are 5200-5500 RPM for best power. Lopey cams may sound cool, but run poorly in a low RPM street environment.
    Use stock cam, stock, GT40 or mildly ported stock heads, Cobra or Explorer/GT40 intake, advanced timing, stock 19 lb injectors, stock fuel pump. Use some good 1.6 or 1.7 ratio roller rockers for extra punch. Use a King Cobra clutch, with stock iron or steel billet flywheel. MAF cars can use a 65 MM TB from the Explorer intake manifold and a 70MM MAF from a 94-95 Mustang. Drive train: 3:55 gears with soft tread compound tires. Use some Ford Racing unequal length headers, stock 2 1/4” cat pipe and some mufflers that don’t drone or get too much attention from the law enforcement or neighbors. The stock computer will handle all this with no problems and doesn’t need any help in 90% of the cases. No skinny or grossly undersize tires for the front: remember you still have to stop quickly in traffic. Make sure all the rubber bushings in the front and rear suspensions are in first class shape. Leave the emissions equipment intact and working. Removing or disabling it won’t get you any more HP or performance. Do not convert to carb or remove A/C: either one will reduce the resale value. Carb conversions cannot be titled for street use or get tags in some places. They definitely won’t pass smog inspections.

    Street/strip: A little more slope to the torque curve with a gently sloping peak. Use slightly larger port volumes on intake and heads for more peak HP. Uses 3.55 or 3.73 gears to get the RPM’s up into a higher range quicker. Be prepared to sacrifice some low RPM throttle response in exchange for high RPM power. This by necessity will be a Mass Air or Mass Air conversion on 86-88 5.0 Mustangs, since stock speed density will not run well with the changes in engine airflow. Don’t get too crazy on any one engine part since you still have to drive the car on the street, and a mismatch can make street driving miserable.
    Use stock or mild aftermarket cam, Ported GT 40, or 165-180 CC port volume aftermarket aluminum heads. Use a Trick Flow, Edelbrock Performer or equal intake manifold. Take a 73 MM aftermarket MAF calibrated for 24 lb injectors, and 24 lb injectors, 155 LPH fuel pump, Kirban adjustable fuel pressure regulator. Be prepared to shell out some $$$ for a custom burned chip using data gathered from a dyno run. Mass market chips will not get the job done. Use some Ford Racing unequal length headers, aftermarket 2 1/2” cat pipe and some mufflers that don’t drone or get too much attention from the law enforcement or neighbors. Drivetrain: expect the stock T5 to fail, so save your money for a super duty 5 speed trans. Tremec 3550, TKO 500 & TKO 600 are the best choices. Different gears in a stock T5 case work for some, but there is only so much power you can pass through a T5 in race mode before it breaks, even with stronger gears. Next are the Chassis mods: full length subframe connectors, different springs, different shocks, aftermarket lower and upper control arms with rubber or urethane bushings. Buy all the parts from someplace like Maximum Motorsports, Griggs or Steeda as a kit so that you know that all the parts fit and don’t argue with each other. Carry spare tires and wheels for the drag strip: skinnys for the front and drag radials for the rear. No skinnys for street driving! Over 85% of the breaking power is generated by the front tires, so skinnys won’t do the job in a panic stop situation. Disconnect the front anti-roll bar at the strip; reconnect it before you drive home. Leave the emissions equipment intact and working. Removing or disabling it won’t get you any more HP or performance. Do not convert to carb or remove A/C: either one will reduce the resale value. Carb conversions cannot be titled for street use or get tags in some places. They definitely won’t pass smog inspections.

    Strip only: High RPM, High flow heads (185-215 CC port volume), wild cam, high flow intake manifold, 70 MM or larger TB, 80 MM or lager MAF, strip everything out of the car that doesn’t make it go faster. Carbs are OK if that’s what you want, but remember that as the temp/humidity/ barometric pressure/altitude changes, you have to re-jet and readjust the carb. EFI eliminates most of that with its built in compensation or you can tune of the fly with a high end Motes or Tweecer system combined with a wide band air/fuel ratio meter. Use custom headers, dumps and minimal mufflers. How fast you can go on 5 liters is a function of the skill level of the driver/mechanic and the size of your wallet.

    TRAILER the car to the race track since it won’t be legal to drive it on the street. Drag slicks in the rear, skinnys up front, use 3.73 or bigger gears (4.xx) in the rear axle. Since you won’t be driving on long trips, the big gears with work with the high RPM power curve to get the best results. Drivetrain: TKO 500 & TKO 600 are the best choices. Different gears in a stock T5 case work for some, but there is only so much power you can pass through a T5 in race mode before it breaks, even with stronger gears. Next are the Chassis mods: full length subframe connectors, different springs, different shocks, aftermarket lower and upper control arms with rubber or urethane bushings. Buy all the parts from someplace like Maximum Motorsports, Griggs or Steeda as a kit so that you know that all the parts fit and don’t argue with each other. Remove the front sway bar, put an airbag in the rear spring of the side that spins the tire the most. Plan on a roll cage if you are truly serious about going fast: most strips will require it once you get to a certain ET range.

    Autocross is a combination of Hot street engine and street strip chassis prep. The engine must accelerate quickly from low RPM and needs a broad, flat torque curve. Next are the Chassis mods: full length subframe connectors, different springs, different shocks, aftermarket lower and upper control arms with rubber or urethane bushings. Buy all the parts from someplace like Maximum Motorsports, Griggs or Steeda as a kit so that you know that all the parts fit and don’t argue with each other. Most of the time you’ll never hit third gear, so some 3.73 or bigger gears (4.xx) may help a lot. You’ll have to spend some more money on brakes since it kills brakes quickly. Rear disks, larger rotors up front, stainless steel brake lines, different brake pads. A 87-88 T Bird Turbo Coupe or SN 95 rear axle will be your best bet. Autocross will severely strain 1st & 2nd gears, so your T5 may take a premature dump. Save your money for a super duty 5 speed trans. Tremec 3550, TKO 500 & TKO 600 are the best choices.

    All out road race is the most difficult of all: an engine that will run at high rpm hour after hour and never fail, yet pull hard out of the hairpin turns that will require a lot of torque at lower RPMs. In my opinion, guys that can successfully build a winning road race engine are the cream of the crop. Top this off with a chassis built for strip only duty, but with changes to the settings of springs, tires, roll bars brakes and shocks. It’s a whole other world of racing.
    You’ll have to spend lots more money on brakes since it kills brakes quickly. Rear disks, larger rotors up front, stainless steel brake lines, different brake pads. Air ducting to cool the brake rotors will be a must. The brake rotors of cars on a high speed road course glow red after several hard laps of racing. Drivetrain: TKO 500 & TKO 600, and T56 close ratio are the best transmission choices.

    On a budget? do the junkyard upgrade...

    Gears - 87-88 T-Bird Turbo Coupe rear axle - disc brakes and 3.55 or 3.73 gears in one package for $125-$300. Add another $100-$200 or so to complete the brake upgrade.

    94-95 Mustang GT MAF - $40-$100. It is 70 MM instead of the stock 55 MM on regular stangs built prior to 94. It uses a slip on duct on the side that goes to the throttle body and a 4 bolt flange on the other. You need a flange adapter to fit the stock slip on air ducting that goes to the air box. Wiring plugs right in with no changes. *1 *2

    95-97 Ford Explorer intake manifold & throttle body $150-$300. The intake manifold flows 220 CFM +, much better than stock. Throttle body is 65 MM, bigger than the 60 MM on stock stangs. I got a 96 with EGR passages that match the stock setup, so my smog gear works just like factory. You’ll need a 65 MM EGR spacer & new gaskets for $65-$90 so you have a place to mount the EGR & throttle linkage.

    3G alternator from 94-95 Mustangs or other Ford. $20-$120. A must have to make the electrical system work like it should or if you have an electric fan. You’ll need a 4 gauge power wire and a 125-135 amp fuse to go with it about $15- $30.

    Lincoln MK VIII electric fan -$40-$160. Free up some HP by not having to drive the stock fan. The 3G alternator upgrade is a must have prerequisite before you do the MK VIII fan. You won’t have enough electrical power if you don’t do the 3G upgrade.

    Aluminum driveshaft: (courtesy of shawn13) It needs to be from a 92-93-94 Aerostar AWD. It measures 45 ½” center of the front U-joint to center of the rear U-joint. You will need the U-joint, part #PUJ353 from NAPA. The Canadian NAPA pat number is 1-0134BF. It should bolt right up after the U-joint swap.

    Note: This driveshaft is not an exact duplicate of the Ford Racing part. It is 3” in diameter while the Ford Racing part is 3.5” in diameter. There is no guarantee that the balance will be any better than the stock part.

    Use a piece of string and wrap it around the driveshaft. Make a mark on the string where the ends overlap. Measure the length of the string:
    On the 3" AeroStar driveshaft the string will be 9.42" or about 9 7/16" long.
    On the Ford Racing 3.5" driveshaft the string will be 10.99" or about 11" long

    *1.) Metal flange adapter http://www.kustomz.com/components.html Buy the TR70 for $40. Or spend some time on eBay looking for one that may fit.

    *2.) MAF & sensor interchange
    The 94-95 Mustang 5.0 MAF & sensor is also found on:
    1995-94 Mustang 3.8L F2VF-12B579-A2A,
    1994-92 Crown Victoria 4.6L F2VF-12B579-A2A,
    1995-94 Mustang, Mustang Cobra 5.0L F2VF-12B579-A2A,
    1994-92 Town Car 4.6L F2VF-12B579-A2A,
    1994-92 Grand Marquis 4.6L F2VF-12B579-A2A,
    Evidently the –A1A, -A2A, AA, etc. on the end of the part number is a minor variant that did not change the operating specs. You should be able to ignore it and have everything work good.
    Illuminator likes this.
  9. justinb2488

    justinb2488 New Member

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    Great thanks for all of that. Not sure exactly what MAF is. Does my 91 gt have MAF on it or do I need to get one?
  10. GroverDill

    GroverDill GoldMember

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    subframe connectors and gears. As far as used heads go, in my opinion they are only a good deal if you can bolt them on as is. I feel you start putting money into "bargain used heads" and the bang for the buck goes out the window.
  11. jrichker

    jrichker StangNet's favorite TOOL SN Certified Technician Founding Member

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    Every fuel injected Mustang made after 1988 had a MAF. The Mass Airflow Sensor (MAF) measures the amount of air entering the engine. The computer uses that data to help calculate the correct air/fuel mixture.

    Here's a book that will get you started with how the Ford electronic engine control or "computer" works.

    Ford Fuel Injection & Electronic Engine Control 1988-1993 by Charles Probst :ISBN 0-8376-0301-3.

    It's about $25-$40 from Borders.com see http://www.amazon.com/ . Select books and then select search. Use the ISBN number (without dashes or spaces) to do a search. Try searching using M-1832-Z1 instead of the ISBN number if you don’t get any positive results. You may only be able to find a used one, since the book is as old as the cars it covers. Or you order it from your Ford dealer as SVO part no. M-1832-Z1.


    Use the ISBN number and your local library can get you a loaner copy for free. Only thing is you are limited to keeping the book for two weeks. It is very good, and I found it to be very helpful.
  12. Mustang5L5

    Mustang5L5 Car used in adult film "Highway Gangbang-InDaButt" SN Certified Technician Founding Member

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    First thing I'd do? Go through the car and get it running 100%. Run the codes, tune it up, make sure all the fluids are fresh and the car is running the best it can.

    Then research. Some guys spend MONTHS debating their combos. Then buy the parts and do the work once. Buy a cam that works with the heads you want to run that is matched to a good intake, etc etc.
    88LX5.Oh likes this.
  13. 88LX5.Oh

    88LX5.Oh Advanced Member

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    Here's the BEST advice you'll get for any engine build. Buy the cam last. Don't buy a cam and then build around it.
  14. mikestang63

    mikestang63 Mustang Master

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    Why are you looking to swap heads? For what purpose. That is not the "first thing" to do. The first thing is to have a goal and a purpose. Is this going to be a weekend street car, see any drag use, or just a cruiser? These things have a way of starting off small and then taking on lives of their own, Best thing is to have a budget and then determine what you want to do within that budget.

    Swapping heads but keeping the stock throttle body, MAF, intake, exhaust is a waste of time and money.

    IMO the first thing to do is make sure the car is in proper working order. Tune up, change and flush all fluids- oil, trans, rear, coolant, make sure brakes, suspension, coolant, drivetrain, electrical, are all in good working order. Check all belts/hoses/filters/tires. Check torque boxes. SAFETY FIRST. Before you do any mods make sure the car is safe and in good working order. I guarantee there are items that need attention.

    Then the first mods I would do are some FREE MODS

    Remove air silencer in stock airbox located in passenger side inner fender
    bump timing to 14 degree BTDC- must run premium fuel
    make sure tires properly inflated

    Next, the first mods to look at are
    Gears- about $250 for the gears and install kit. Another 3-400 for labor
    3.55 if stick
    3.73 if auto

    Subframe connectors $150 for good full length. Another 50-100 for install, Must be welded in. Do not get the bolt in type

    Exhaust- used headers-100-200, h pipe- 50-150, mufflers and cat pipe- 100-200, gaskets. bolts,- another $30.. labor to install full exhaust 200-400

    good set of headers and a cat back system. Personally if you live in a state with no emissions, you can remove the smog pump and hoses, stock mid pipe and swap in an off road H pipe.

    Throttle body and MAF. Used 25-50 for TB 35-50 for MAF

    You can go to any junkyard and get a 65mm throttle body from mid 90's explorers and a 70MM MAF from a 94-95 mustang GT.

    Upgrade alternator- Used 40-60 Wiring 40

    the stock 75 amp alternator and wiring are woefully inadequate and a fire hazard IMO. At the junkyard find any 94-2000 mustang 3G 130 amp alt. Have it tested for free at autozone before installing. Buy the install wire kit off Ebay or the Corral. There are many install writeups on this.

    Taurus or Lincoln electric fan and controller- Used fan40-60 New flex a lite 33054 or DCC controller 110-130 wires, shrink wrap, misc connectors, fuses, etc 20-30

    Under drive pulleys- Used 50-100 new 100-150 Notice I put this after the alternator and E fan. Don't think of putting these on with the stock 75 amp alternator. Do not put on a race crank pulley. Know that there are different kits for stick vs. auto. Your cooling and charging systems need to be in good shape before putting these on.

    HP costs money. Figure 800-1000 for a simple used explorer intake, heads, throttle body swap when you factor in the parts, swapping the valve springs on the explorer head for better ones, machine shop for the heads, tapping the explorer intake for the IAT and EGR coolant tubes, head/intake/exhaust/ thermostat gaskets, various rtv/fluids, new head/exhaust bolts, new thermostat, and other misc. That would give you 260-270 hp.

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