EFI Intake Heat Spacers

Install Intake SpacerClaimed Performance Gains
Install Throttle Body SpacerSuppliers
   

Background

The 3.8L V6 Mustang electronic fuel injected (EFI) engine has an aluminum intake manifold that consists of upper and lower intakes.   The lower intake contains passages that circulate cooling water from the radiator.   The upper intake does not.   They can both get very hot.   When that engine heat is passed on to the intake air it degrades performance.

EFI intake heat spacers fit between the upper and lower intakes to insulate the the air in the upper intake from this engine heat.   Air passing through the throttle body can be further insulated by adding a spacer between the throttle body and the upper intake.   Phenolic is used as the spacer material beacuse it has excellent insulating properties and a coefficient of thermal expansion that is similar to that of aluminum.   Once you install these spacers, the upper intake and throttle body run cooler, there is less heating of intake air, and less power is lost when the engine runs hot.  

Adding an intake spacer also has the effect of lengthening the intake runners.   It has been claimed that this adds low end torque, and there have been tests that seem to confirm that, as described at the end of this article.

These spacers have been around for a long time.   Shown above are examples of intake spacers for the 5.0L Mustang V8.   They are sold by Ford Motorsports, BBK, Edelbrock, Moroso, and others in a variety of thicknesses.   None of these manufacturers currently produce spacers for the 3.8L V6 Mustang.   I purchased the spacers in this article from Canadian Mustang enthusiast Branko Kolic, but he is apparently no longer making them.   See Suppliers below for current sources.

Installation - Intake Spacer

A. Remove the Upper Intake Manifold


  1. Disconnect the battery ground cable (8mm).
  2. Remove the air intake tube from the throttle body.

  3. Disconnect the vacuum tube (A) and the idle air control solenoid (B)
  4. Disconnect the throttle position sensor (C) and the evaporative emissions return tube (D)
  5. Disconnect the accelerator and cruise control cables (E) from the throttle body.
  6. Disconnect the accelerator and cruise control cables from the bracket (F).
  7. Remove the solenoid bracket bolts (G) (10mm).
  8. Disconnect the positive crankcase ventilation tube (H) .

  9. Disconnect the two vacuum tubes (I).
  10. Remove four bolts (7mm) and position the coil (J) aside.
  11. Disconnect the vacuum hose (K)

  12. Remove the 12 bolts (8mm) that secure the upper intake.   Make note of which are the long bolts, so that they can be reinstalled correctly.   Then lift off the upper intake.   It's easiest to do this when the engine is cold.   I used a piece wood as a pry bar to carefully separate the two manifolds.

  13. Carefully scrape off any gasket material left around the upper and lower intake ports.

B. Install the Spacer & Gaskets

Above is the 3/8" phenolic spacer and one of the two gaskets needed for this installation.  The Ford part number for the gasket is shown.

Note that their are two alignment pegs in the lower intake.   They fit into holes in the upper intake and ensure that the ports are precisely aligned.   Once you install a spacer, these pegs no longer reach the upper intake.   To ensure proper port alignment, you need to install longer pegs that extend through the spacer.   Two pieces of 5/16" dowel work fine.

One gasket goes on the lower intake, then the spacer, then the other gasket.   In this picture the longer alignment pegs have not yet been installed.   You can see that the spacer is nicely gasket-matched.

C. Reinstall the Upper Intake Manifold

  1. Place the upper intake manifold on top of the spacer and gaskets.   The alignment pegs should hold it firmly in place (no side to side movement).  

  2. Put some anti-seize lubricant on the threads of one of the upper intake bolts, then insert and start that bolt to align the spacer and gaskets.  Then do the same with the remaining bolts.   Turn them all until they are just finger tight.

  3. Using a torque wrench that reads in inch-pounds (in-lb) tighten the bolts in the sequence shown above in three stages.  (If you don't have a wrench that reads in inch-pounds, divide by 12 to get foot-pounds.)

      Stage 1: Tighten to 53 in-lb.
      Stage 2: Tighten to 71 in-lb.
      Stage 3: Rotate an additional 90 degrees.

  4. Connect the vacuum hose (K).
  5. Install the ignition coil (J). Tighten mounting bolts (7mm) to 53 in-lb.
  6. Connect the vacuum tubes (I).
  7. Connect the PCV tube (H).
  8. Install the solenoid bracket bolts (G) Tighten bolts (10mm) to 89 in-lb.
  9. Connect the accelerator and cruise control cables. (E/F)
  10. Connect the TP sensor (C) and the EVAP return tube (D).
  11. Connect the vacuum tube (A) and the idle air control (IAC) solenoid (B).
  12. Reconnect the air intake tube to the throttle body.
  13. Connect the battery negative cable (8mm).

Installation - Throttle Body Spacer

Shown above (left) is a 1/2" throttle body spacer.   On the right is an adapter for the throttle cable bracket, which moves the cable 1/2" closer to the throttle body to maintain throttle linkage geometry.   You will also need four longer bolts to mount the throttle body.   Shown at the bottom are four hex-head metric M6x40x100 pitch stainless steel bolts with washers that I purchased at Ace Hardware.

A. Remove the Throttle Body

  1. Disconnect the battery ground cable (8mm).
  2. Remove the air intake tube from the throttle body.
  3. Disconnect the throttle position sensor (C) and the evaporative emissions return tube (D)
  4. Disconnect the accelerator and cruise control cables (E) from the throttle body.
  5. Remove the two bolts and the two nuts (on studs) that secure the throttle body.
  6. Remove the throttle body studs.

    Hint:  If you put two nuts on the stud and tighten them against one another (shown above), then you can put an open-end wrench on the inner nut, and easily back out the stud.

B. Remove the Throttle Cable Bracket and reinstall with the Adapter

C. Reinstall the Throttle Body


  1. Insert the 1/2" spacer and two new gaskets (I reused the stock gasket on one side and silicon gasket-maker on the other).
  2. Put some anti-sieze lubricant on the four M6x40X100 hex head bolts and reattach the throttle body.   Torque the bolts to 12-18 ft-lbs.

  3. Connect the accelerator and cruise control cables. (E)
  4. Connect the TP sensor (C) and the EVAP return tube (D).
  5. Reconnect the air intake tube to the throttle body.
  6. Connect the battery negative cable (8mm).

My Results?

My upper intake definitely runs cooler on the highway after installation of a spacer.   I've run for an hour at 80 mph, pulled into a rest stop, raised the hood, and found the upper intake cool to the touch.   But once air is no longer flowing through the intake, it quickly picks up the ambient heat in the engine compartment.   I'll guess that the intake now cools down quicker than the engine, but I have no measuring equipment to confirm that.  There seems to be a change in throttle responce - for the better.   Since this installation, my 1/4 mile E.T's have dropped, so I can safely say that the the spacers did not hurt my car's performance at the track.   They may have helped it a bit by allowing the intake to cool quicker between runs.   Some people say they get significant torque and horsepower gains from installing these spacers.   You can read one such claim below.

Update: 10 June 2003: - CLAIMED PERFORMANCE GAINS - The Mustang parts vendor Extreme Effects LLC conducted dyno tests on 1994-1998 3.8 L V6 Mustangs equipped with an intake spacer and found that the addition of the spacer produced a gain of 7.2 ft-lb of torque and 6 h.p..  The gain in torque was attributed to the fact that the spacer lengthened the intake runner.

Update: 30 May 2005: - ALIGNMENT PEGS - When I pulled my intakes to port and polish them, I could tell from discoloration on the spacer that the upper and lower intakes were slightly (1/8") misaligned.   Apparently, when I installed the spacer I did not extend the alignment pegs in the lower intake, and without those pegs engaging the upper intake there was sufficient play in the bolt holes to allow this 1/8" shift.   I've added comments above about the need to extend the alignment pegs when installing a spacer.

Update: 15 June 2007: - SUPPLIERS - Two current suppliers of 94-98 V6 Mustang (singleport) and 99-04 V6 Mustang (splitport) spacers are Veracity Auto Parts [www.vapauto.com] and Jeff Magnuson   [jeffrey_magnuson@wsu.edu]