(Similar installation on 4.6L Cobra)

Written by Mustangworld.

Lots of pics, I hope your on the net at 28.8 or faster.

Stang on stands, w / ramps as a backup.
Time to lift the stang again and throw in a Mac Pro Chamber (off-road) H-pipe !

First off, keep in mind that in most states it is not legal to drive on public streets without catalytic converters, and it's illegal to tamper with any smog equipment in your stang (unless damaged) but you can do whatever you want to your stang for off-highway (racing) use, this procedure CAN void your new car warranty (in most cases, at most dealers). Though many 4.6L Mustangs have passed smog tests with the Pro Chamber in place.

Our 4.6L SOHC SOUNDS AWESOME ! With the Mac Pro Chamber AND our Mac Cat-back system in place, our stang sounds like a full blown racer. The overhead cam valve chatter sounds intense with a free flow exhaust, kinda like a 351c with high lift cams and heads. It's a unique sound all it's own that screams "Go ahead, make my day". Cars now keep their distance, dogs don't cross the street in front of you anymore (at the track of course :-). This exhaust note is very controllable, which is why we love the Mac anti-reversion mufflers. If you want more chatter then step on the gas, want a low "boom box" constant tone then lift up on the gas pedal. We can't go into a "whisper mode" anymore like we could with just the cat-back in place, but we can get into a quiet "earthquake" type low end rumble mode if we need to. This is a great "poser" mod, NO ONE wants to race us on the street anymore (uh, I mean at the track :-), the exhaust note is THAT intimidating!

This will finish off our exhaust system mods, we went with a 2 1/2 Mac system throughout for a perfect torque curve match (with the stock heads) when we finally throw in the intake mods (supercharger, throttle body, etc.) We left the stock headers in place because with the stock heads, we did not want to loose any HP for the moment. Low end torque remains the same, but we have a higher HP "feel", 9-14HP peak extra at higher rpms (on the bone daddy stock engine). Until we get the intake side of the engine mods going, we won't see any great increase in HP at the low end of the RPM spectrum. With the 2 1/2 system we didn't loose any low end torque on the stock engine despite the back-pressure changes.

CHECK ENGINE LIGHT AND OBD II. As you will see below, Mac has engineered this h-pipe very well, in the 4.6L ECC5 computer there are 4 oxygen sensors on the h-pipe (as opposed to only 2 sensors on the 5.0 ECC4). 2 sensors BEFORE the 6 catalytic converters, and 2 AFTER the catalytic converters, two sensors on each exhaust side. Mac has placed the rear 2 sensors at the hottest place in the pipe flow (just before the "Pro Chamber"), this is the hottest place within reach of the sensors. This reduces the effects of removing the cats to the computer (but does not eliminate the chance of a check engine flag).

MAC (nor any other manufacturer) DOES NOT guarantee that you will NOT get a check engine light illumination. If the check engine light DOES come on you have a few choices: 1) Disconnect your battery overnight and reset your computer. 2) Re-program your ECC5 computer for the mod (with an ECC programmer). 3) Buy a computer chip that takes care of the problem in it's programming. or 4) Put variable resistors in-place where the sensors would normally go to "fool" the computer. None of these methods are guaranteed to work (but do in most cases). Re-programming your computer or buying a "chip" with the new "off-road" h-pipe programming is the best way to go, to ensure 100% proper engine performance (this is what we are doing).

Once again we turn to Mac for exhaust. Their Pro Chamber h-pipe is a unique piece in aftermarket h-pipes. This h-pipe has a "Pro Chamber" where normally a piece of "blow-by" pipe would be. This larger area greatly aids in the merging of exhaust gases for increased heat and exit velocity. Also, like our entire Mac exhaust setup, THERE ARE NO MUFFLER U CLAMPS ! Don't get us wrong, muffler clamps work great, but we've had our problems with u-clamps in the past and love the fact that our exhaust looks "factory" and totally trick with no muffler clamps in sight. We can also un-install the h-pipe with ease because Mac uses standard 11/16 nuts for the ENTIRE exhaust system, with u-clamps, you'll need a small socket for your muffler clamps and another for your flanges. Also if you are using u-clamps and you over tighten them, you will "kink" your exhaust tubes, making installation / removal even harder, and don't loose the 2 metal pieces associated with each clamp, and two nuts per clamp.............. basically, you can see why we think the Mac system is THE BEST, they manufacture the h-pipe AND the muffler cat-back system, both were made for each other and fit like a glove.

Installation is easy, but clumsy. We have 24hours access to a nice car lift, but that would have been no fun :-) Actually, everything we do here at Mustangworld we want to make sure you can do yourself with standard tools and jackstands / ramps.


1. This is the Mac Pro Chamber h-pipe, a unique piece in aftermarket h-pipes. Note the mounts for the oxygen sensors on the pipe. Also note the pipe is flanged (two pieces) on one side for ultra ease in installation. It comes with one Gasket and bolt hardware. The Pro Chamber "looks" like a catalytic converter in the center :-) Cost $229.00 The Pro Chamber !
2. Here is the stock h-pipe with6 catalytic converters in place. You can see our Mac Flowpath muffler cat-back system in the rear. If your stang is already lifted, lets go to the next step. Stock H-pipe w / 6 catalytic converters
3. The next step is to remove the oxygen sensor (wire plugs). In the front they are located close to the headers and are marked green. In the rear they are marked blue and purple. You also need to remove the wire harness from the black tray that is bolted to the stock h-pipe. It is held to the tray with standard plastic rivets that pop out. You can also remove the oxygen sensors at this time, MARK THE LOCATION OF EACH SENSOR AND TRANSFER THEM TO THE NEW H-PIPE IN THEIR EXACT LOCATIONS. Removing the O2 Sensor plugs
4. Now we can un-bolt the stock h-pipe. Starting with the rear (Fig.A) , then un-bolt the h-pipe from the headers with a long socket extension (Fig.B). Now we must remove the H-pipe from it's 2 rubber hangers (near the rear) it's like a muffler hanger. Step 8 shows this hanger. Then carefully drop the h-pipe out. Fig.C shows the driver side unbolted, Fig.D shows the passenger side done. You need to carefully remove a thin metal gasket from the header on the passenger side,SAVE THIS GASKET, you'll need it when you re-install the stock h-pipe! un-bolting the stock H-pipe
5. The two 2 h-pipes side-by-side. We recommend removing the sensors from the stock h-pipe while the h-pipe is still up, they can get damaged when you drop the stock h-pipe, but if you did not then, you can remove them now and transfer them to the new pipe in their EXACT positions. Don't swap sensor locations. The two front sensors are NTK's F5MF-9F472-AA units. In the rear you got Driver side: F6DF-9G444-AA and passenger side:F6ZF-9G444-AA. A different rear sensor for each side! h-pipes side-by-side
6. Make sure you check each mounting location on the new h-pipe for any stray metal, if you see anything blocking the opening or threads then knock it loose with a screwdriver, then thread the oxygen sensor into place. The Pro Chamber has a split (and flanged)end on one side. Attach this tube to the main h-pipe with a mild tighten on the bolts so we can install the h-pipe as a single unit. Oxygen Sensor
7. Next, transfer the black metal wire harness tray over to the new h-pipe. Use the bolts and nuts from the stock h-pipe. The Pro Chamber has a mounting location for it. Transfer the wire harness tray
8. Now we can put the new h-pipe in place. At the header, the driver side bolts right on, on the passenger side you use the supplied gasket to ensure a tight seal. Use two small rubber bands to hold the gasket in place. Finger tight the bolts to hold the front part of the h-pipe up to the headers. Fig.A shows the h-pipe hanger. It's two rubber pieces attached to the tranny. Using dish soap, (to install / remove) work the Pro Chamber into these rubber mounts. Fig.B shows the h-pipe at the muffler tubes. Fig.C shows the new pipe on the ground. Fig.D shows the pipe in place at the header (passenger side). bolting on the new h-pipe
9. The Pro Chamber in place. In the rear mate the h-pipe end with the muffler tubes and finger tighten the bolts. Once everything is hanging, you can fully tighten the whole system starting at the headers on-back, while holding the pipe in place for chassis clearance. Now plug in the wire harness to the tray (in the rear) and plug in all 4 of your oxygen sensors (front and rear). Rear O2 Sensors and h-pipe hanger location
10. Now we have a "Mac - back" system in place. Pro Chamber and cat-back. This means we have no catalytic converters on the exhaust for off-highway racing use. No cats means better flow and a much louder stang. Also, we don't want to burn out our cats when racing anyway. Pro Chamber Done !

WANNA HEAR IT? Click Here.

Because there are some who will be removing and installing the h-pipes very often for off highway race use, we decided to include some more tips for the 4.6L. Some may choose to leave the Pro Chamber on at all times but if you "get caught" you may get fined. Some may need to re-install the stock pipes for sound control in restricted areas (like an old folks home, etc.).

Install tips:

1) When removing an H-pipe, careful not to bang up the oxygen sensors on the chassis. We recommend removing the O2 sensors while the h-pipe is still up on the stang.

2) The passenger side header uses a gasket and flange, you may need to order a few extra gaskets for constant removal / installation.

3) When installing the passenger side gasket, use two small rubber bands at the ends to hold it in place, this will make installing the h-pipe much easier. The small rubber bands will naturally "burn up" (while driving) and you'll be left with the gasket in place. The stock metal gasket is barbed on one bolt side and stays in place by itself.

3) The passenger side header uses two bolt studs that may "back out" as you are removing an h-pipe. If this happens, you'll need a "stud socket" to re-tighten the stud(s) back into the header. Eventually these studs will get loose and you can just screw it into the header with your fingers no problem. The driver side header (on the 4.6L) uses a traditional gasket-less ball flange.


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