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How to install a MAC Off-road Pro Chamber Mid-Pipe on your 1999-2004 (GT, Cobra) Mustang

Installation Time

2 hours

Tools Required
  • 9/16’’, 18mm, 8mm deep well 3/8’’ socket
  • 7/8’’ box end wrench
  • Never-seize lubricant
  • Penetrating lubricant
  • Floor jack
  • Jack stands

MAC Offroad Prochamber Shorty H Pipe Install Guide

Install Vehicle: 2003 Ford Mustang GT Automatic


Note- O2 sensor extensions are not necessary for this install.


1. Disconnect battery using an 8mm socket
2. Jack up car using car lift or floor jack and support car with jack stands
3. Spray 4 studs at the front
and 4 in the rear of the stock h pipe with penetrating lubricant
4. Disconnect O2 sensors


5. Remove nuts from exhaust flanges connecting stock h pipe to catback system using a 9/16’’ deep well socket. Note: Keep the stock h pipe supported on the catback by leaving the studs in, meaning, just remove the nuts.
6. Disconnect the upper bolts with a 9/16’’ deep well socket (if doing a header install,
the upper bolts do not have to be removed, the entire manifold and stock h-pipe can be removed in one piece)


7. Carefully remove stock h-pipe. Use a friend to help lower h-pipe.
8. Remove the 2 - O2 sensors using a 7/8’’ box end wrench and install on new
ProChamber h-pipe. Do one at a time to keep them straight, because they need to go back on the same side as the original h-pipe.


9. Install the new supplied studs in the catback side flanges, applying never-seize first


10. Lift ProChamber H-pipe into place, supporting the h-pipe by finger tightening the supplied nuts onto the studs. A friend is very helpful to support the ProChamber while you are tightening things up, but it can be done without help.
11. Finger tighten manifold/header size flange nuts onto studs
Note: I had problems making these flanges fitting! This can be seen in the picture below. To remedy this, I had to use a floor jack and block of wood to lift the header side carefully



12. Tighten the manifold/header side flanges reusing the original nuts with a 9/16’’ socket, or with the supplied hardware that came with the headers (mine was a 18mm)


13. Tighten the catback size flanges with a 18mm socket. Do not overtighten! It is really easy to go back and torque down later if there is a leak. The same cannot be said for stripping out the nuts or studs.
14. Connect the O2 sensors to their plugs. To do this, remove the plugs from their clips to allow for extra length. Then ziptie the plugs back to the holes on the plug bracket. O2 sensor extensions are not necessary for this install.


15. Lower the car, reconnect the battery (8mm) and start the car. Let your Mustang run for several minutes, until there is no more smoke (the smoke is just the anti- rust oil added to the ProChamber)
16. If there are any leaks, find them by sound and tighten the flange bolts


This guide was created by American Muscle customer Tyler Smith on May 26, 2015

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