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Herd WebMaster
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USA
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Posted - 05/07/2007 :  10:59:06 AM  Show Profile  Visit Herd WebMaster's Homepage  Reply with Quote
Export Pipe Information
By Scott Mueller.

What we are calling "Export Pipes" are the GM factory Regular Production Option (RPO) code NM8 (Leaded Fuel System), which is an export option consisting primarily of pipes that replace the catalytic converters on cars that are shipped to Gulf Coast countries such as Saudi Arabia. Cars in that part of the world still run on leaded gasoline, which is incompatible with catalytic converters and O2 sensors. Both Impala SS (actually called the Caprice SS in that form) and Caprice models were exported with this option.

Installing these pipes on an Impala or Caprice will significantly reduce backpressure in the exhaust, increase power by 10-15 HP, and also make your existing exhaust sound louder than it is now. If you have one of the louder aftermarket systems the combined result may be too much, however the export pipes work beautifully with the stock exhaust or with other quieter systems like the Borla. With these systems you get a nice mellow sound, and a real growl when you step on the gas.

The actual export pipes themselves as well as the other GM parts which are part of the RPO NM8 option are available from any GM dealer under the following part numbers:
Part # Description Cost Notes:
10204015 LH Export Headpipe $50.49
10204014 RH Export Headpipe 50.49
10168551 Exhaust Gasket 3.91 Qty. 2 required
12551380 94 Export Emissions Sticker 4.95 "NON-CATALYST"
10243957 95 Export Emissions Sticker 4.95 "NON-CATALYST"
12555992 '96 Export Emissions Sticker 4.95 "NON-CATALYST"
10135488 Export Fuel Inlet Pipe 22.77 w/o fuel nozzle restrictor
14090316 Export License Bracket 15.15 w/o "unleaded fuel" embossed

After acquiring the pipes and other parts, there are several items to consider in preparing them before they can be installed.

Shower Drain Removal:

The export pipes each have a flow restrictor spot welded at one end of the pipe that looks very much like a shower drain. You will most definitely want to remove these "shower drains" for maximum exhaust flow. The best way to remove these restrictors quickly and with no damage to the pipe is to use a ratchet wrench socket to knock them free of their spot welds. First get the largest ratchet wrench socket that you can fit inside the pipe (something about 2" to 2-1/4" or so works best), then hit the socket sharply with a hammer to drive the shower drain further into the pipe, thus breaking it free of the spot welds on the sides. Then just twist it sideways and pull it out
with a needlenose pliers. It takes about 1 minute to do both pipes using this technique!

Oxygen (O2) Sensor Bungs:

The stock catalytic converter pipes are equipped with one or two O2 sensor bungs each. These bungs are 18x1.5mm threaded collars which are welded to the pipes in order to accept screw-in O2 sensors. The '94 and '95 cars have pipes with only one bung each, and that bung is attached upstream from the catalytic converter on each of the pipes. The '96 cars with OBDII include the same primary bung on each pipe upstream of the converter, and also a second bung on each pipe aft of the converter (downstream).

The first set of bungs (upstream) are for the primary O2 sensors, which are used by the PCM to calculate the proper fuel delivery and thus adjust fuel injector pulse width. The second set of bungs on the '96 cars only are for the secondary O2 sensors, whose sole purpose is to allow the PCM to detect whether the catalytic converters are present and functioning correctly.

Since leaded fuel destroys O2 sensors, the export pipes do not have either set of bungs installed. Note that actual NM8 equipped cars have a special wiring harness and PCM calibration which does not use O2 sensors to control fuel delivery. Unfortunately for them this means fuel delivery is not nearly as accurate as on US models, since the PCM would have no idea how rich or lean the exhaust is and therefore cannot compensate.

What we need to do is to obtain a set of 2 sensor bungs total and weld a primary O2 sensor bung on each export pipe in exactly the same position as the same bung is on the stock pipe. Positioning is important, as the bungs are clocked on the pipe such that the O2 sensors will be positioned properly under the car and not interfere mechanically with other components. Use your existing pipes as a guide to mark the export pipes with the exact position the bungs should be installed.

There are several sources of bungs, including the NAISSO SSuperstore, Summit, Jegs, or ATR, however some of those are not true stainless in my experience.

For high grade 316 stainless 18x1.5mm threaded weld-on 02 sensor bungs I recommend contacting JGM Automotive Tools (714-895-7001) and ordering p/n TR-18 (cost $12.60 each). They also sell 316 stainless plugs with copper washers to plug the bungs if you ever want to move the 02 sensors to the exhaust manifolds like I have. Another quick and inexpensive source for bungs would be to obtain an 18x1.5mm stainless nut from the hardware section at a local marine store or from Totally Stainless (800-767-4781).

You will need to take the pipes and bungs to a shop where they can be welded. Be sure the shop knows that these parts are stainless steel so they can weld them properly for long life. The bungs are 304 or 316 (austenitic) stainless steel and the pipes are 409 (ferritic) stainless steel. Usually the welding should be done with a MIG or TIG (Inert Gas) welder and a compatible stainless rod. Before welding the bungs in place, it is recommended that you thread in a sacrificial O2 sensor or 18x1.5mm stainless bolt with PLENTY of anti-seize on it as a plug. This will prevent the bung from overheating during the welding process and protect the threads as well. After welding, remove the plug and you should have clean undistorted threads for your O2 sensors to screw into.

Note that '96 vehicles also have rear O2 sensors, which are installed behind the catalytic converters to test whether they are functional or not. We do NOT want to install bungs for those sensors, instead you will need to order a pair of secondary O2 sensor simulators from Caspers Electronics (847-247-0484). These simulators allow the '96 PCM to believe that the secondary O2 sensors are installed and detecting functioning cats or else the PCM will set a trouble code and indicator light. The simulators are
environmentally sealed (potted) with factory connectors attached, you merely plug them into your wiring harness in place of the secondary O2 sensors and use the supplied tiewrap to attach the simulator to a safe place under the car. The secondary O2 sensors themselves are then no longer needed and can be kept as a set of spares to replace the primary sensor later. As a note I recommend replacing O2 sensors on all vehicles at 50K intervals minimum as standard preventive maintenance.

An interesting alternative is available for O2 sensor mounting. The stock exhaust manifolds have O2 sensor bosses (mounting pads) already cast into them which only need to be drilled and tapped with 18x1.5mm threads to accept the sensors. If you did this then you would not have to weld any bungs into your export pipes. On the other hand, a fringe benefit having the bungs in the pipes along with drilled and tapped bosses in the manifold is that it will give you an optional place to install an EGT (Exhaust Gas Temperature) gauge or backpressure test gauge (or both) in the future.

Coating:

Although the export pipes are made from the same 409 stainless steel as the the rest of the exhaust, 409 is a low grade ferritic stainless alloy that
will corrode. I recommend having the pipes coated with a corrosion proof metallic ceramic coating, which will also serve to insulate the area surrounding the pipes from any heat. There are several companies who offer this type of coating such as HPC or MCCI Jet Hot. The Jet Hot coating is the one I am most familiar with, and is both the name of the company and the coating. They have gloss silver, satin silver, cast iron gray, and black colors available. I recommend the pipes be coated satin silver for a stock appearance or gloss silver if you want them to stand out a little more. Call 800-HEADER-9 for more information.

Installation:

First disconnect the O2 sensors from the stock pipes, remove the three nuts holding the inlet portion of the cat pipes to the exhaust manifolds, and the 2 or 4 bolts on the outlet end attaching them to the rest of the exhaust as well as the hangars. Apply a liberal amount of penetrant oil before removing the nuts and bolts. If the car has high mileage, removing the nuts from the manifold studs may damage the threads. New exhaust manifold studs can be obtained from GM under p/n 10220453 along with attaching nuts under p/n 11516072, although I recommend using stainless steel nuts from Totally Stainless instead. I also suggest replacing the attaching bolts on the outlet ends with stainless bolts, which will make any future replacements much easier.

Apply liberal amounts of anti-seize to all attaching hardware. Move your existing O2 sensors over to the export pipes or install new ones at this time. Then bolt up the pipes using the new gaskets you purchased, preferably with stainless nuts and bolts, and reconnect the O2 sensors to the vehicle harness. If you have a '96, finish by connecting the secondary O2 simulators to the vehicle harness and secure them up out of harms way with tiewraps. At this point I'd recommend firing the vehicle up for leak testing and to listen to the new sound of power!

Finishing touches (for the Anal Retentive among us) :

To complete the NM8 conversion, you can now install the export emissions and tuneup stickers on the upper radiator shroud. Simply peel off the FED stickers that are there now and apply the replacement export stickers in the same position. The new stickers read "NON-CATALYST" and "For Export Only" which complete the factory look of these pipes and really opens some eyes at the car shows. The stickers serve to convince the doubters that this is indeed a true factory option. Tell them you bought the car off the dock just before it was due to be shipped overseas. <g>

Since removing the FED stickers will damage them, I have included for the anal retentive out there the part numbers of the original FED stickers in case you want to want have them on hand to restore later:
Part # Description Cost Notes
12551376 '94 FED Emissions Sticker $4.95 OEM Federal emissions
10243955 '95 FED Emissions Sticker 4.95 OEM Federal emissions
12553939 96 FED Emissions Sticker 4.95 OEM Federal emissions

Now swap the fuel filler pipe on the gas tank for the unrestricted export version. The export fuel filler pipe has no leaded fuel nozzle restrictor in it, allowing quicker and easier refueling even with unleaded since the entire diameter of the tube is open. The fuel filler is attached to the fuel tank with a hose clamp and a few bolts, so it is very easy to change.

A final finishing touch is to swap the license plate bracket with the export version which lacks the "unleaded fuel only" warning embossed into the original. Obviously the emissions sticker, fuel filler, and license bracket are only for the most obsessed individuals, the ones who want this to truly look like the factory option it is.

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