TOG headers / R/T cat install with TOG flex pipe

Written by Ryan D, Member 8574
Applies to the following vehicles: GM 3800 Series 2 and 3 motors
Created 1/24/2004, Updated 12/2/2008

Write-Up Rating
Rated by 8 members

I am making the best and most thorough write-up on installing these headers because there were many points that were not detailed enough causing me to need quite a bit of help. My goal is not just to tell you what to do it is to tell you how to do it. This is not a task for the impatient. I would recommend having a friend help if you are impatient.

With that said I would like to thank John member John Oliver Sal member Silver2KGTP Randy member RatRacer Brad member 2HiPsi and the other ClubGP members that helped me with the information theyve provided.

I have broken the install up into five phases. I think it is a good idea to take a break after each phase is completed. I have heard others say they have completed this install in 5-8 hours but for me this was a rather large project that I spent quite a bit of time on but not all at once. I have a list the parts and specific tools needed. When I started I had all of the tools except the socket extensions and a welder. It is good to have a range of tools before you start this project. I was able to borrow the socket extensions I did not know these were needed when I started but I had to go to an exhaust shop for the welding.

In the steps when I say right I mean the right side of the engine compartment when you are standing in front of the car looking back. The same goes for left. I also suggest reading through the entire install procedure first so you can get an idea of the order that will be taking place. If you use these instructions and have suggestions or notice that something is wrong or missing please contact me.

I have pictures that will be added at a later date. I need to have my roll of film developed. One step specifically says to look at a picture. Until the picture is up I can describe that for you if you contact me.

One more thing that will be added are exact instructions on bending the transmission dipstick tube. For me this is one thing that had to be attempted and failed for me to see the right way to do it. My goal is to make your tube bends a success without having to purchase a new one and retry the bends.




When you start your install remove the following parts preferably in this order to access the manifolds and for working room:

You are now ready to start removing your old exhaust. Its best to start with the down pipe/cat/u-bend section. Removing this allows the engine more movement when you are working behind it.

  1. Jack the car up and support it with jack stands. My jack point was the center of the front bar of the engine cradle. That bar was also the point where I set my jack stands.
  2. Remove the two rubber hangers behind the cat. I used needle nose pliers to do this.
  3. Remove the 15mm bolts from the flange connecting the u-bend and your cat-back exhaust.
  4. Unplug the rear O2 sensor. There is a pin in the harness that must be pulled with needle nose pliers before you can disconnect the harness. This is best done from the passenger side of the car.
  5. Use something to support the pipe under the cat. I used a small box.
  6. Unbolt the down pipe from the rear manifold from underneath the car. Socket extensions come in handy here. These bolts were near impossible for me to move from the engine compartment but they came rather easily from underneath when I used the breaker bar. When the pipe is freed slowly guide it out because you dont want it to bang against your lines.
  7. Remove O2 sensor from the u-bend and place in a safe location. I used channel locks to remove it because I did not have a wrench big enough.

The next piece that needs to be removed is the crossover pipe. All of the bolts are 13mm.

  1. Remove the bolts that connect to the front manifold.
  2. Remove the shield that covers the rear flange.
  3. Utilize your ratchet extensions for the bolts that connect to the rear manifold. These bolts were tough on my car and they ended up snapping and I had 14000 miles on the car at the time of my install. I have heard from others that these bolts are likely to snap.

Take the front manifold off next. All nuts are 13mm.

  1. Label the cylinder numbers on your valve cover gasket and remove your spark plug wires from the plugs and tuck them away or remove them completely. Do not pull by the wire My boots were very hard to get off but keep pulling and twisting on the boot itself.
  2. Remove the nuts for the bracket on the right side and oil dipstick tube on the left.
  3. Remove manifold nuts and studs and save for re-use. The end studs will stay in the head. The center studs will come out with the nuts attached.
  4. Leave the gasket on the head. It can be re-used unless you want to replace it.
  5. Pull the front manifold off and set it aside. I recommend pulling the oil dipstick tube for more working space. It pulls straight up and out of the engine block.

Move on to the rear manifold. All of the manifold nuts are 13mm.

  1. With the car in park go to your driver door and push the car forward. When the car stops you push harder and hit the parking brake. You may also put blocks behind the wheels so the car wont roll back but I used only the parking brake most of the time. My engine didnt go as far forward as I had read about but I had enough room to work.
  2. Label the cylinders on the valve cover and unplug your spark plug wires and move them aside.
  3. Unplug the O2 sensor from the plug on the rear engine bracket.
  4. Remove the wire clips from the rear brackets with needle nose pliers and tuck the wire bundles out of the way. Remove the nuts for the brackets and then take the brackets off. Remember the location of the wire clips.
  5. Remove transmission dipstick tube. It is held in place with one 10mm nut. After the nut is removed you can lift the dipstick tube out of the transmission case. Have pan ready for drips. I wasnt expecting any since I was on level ground but I got plenty.
  6. Remove the EGR nut. The EGR is on the right of the rear manifold near the throttle body.
  7. Remove manifold nuts and studs and save for re-use. As on the front the end studs will stay in the head and the center studs will come out with the nuts.
  8. Pull the manifold up and out of the engine compartment and set it aside.
  9. Leave the gasket on the head for re-use or pull it if you decide to replace it.
  10. Remove the O2 sensor from the manifold and set it in a safe place.


I still need to do this correctly in order to write up on it. I can tell you that you do need a bending tool. I will include pictures and I should have a write-up no later than the end of February.


The first part of your new header set that you will install is the rear header. You should feel like youve accomplished a lot at this point because you have.

  1. Leave the engine pulled/pushed forward. If you returned it to resting position follow step one in the removing stock manifold section.
  2. Get the header in place by ping it down pipe first behind the engine. When you cant move it any farther tilt it towards the right and angle it in place. I didnt have to force it in place and you shouldnt either. Align it on the two end studs.
  3. Start the first and last manifold nuts but only finger tighten at this point.
  4. Start the EGR tube nut. Be sure to watch the end of the tube and make sure it is going in perfectly straight. Mine didnt want to fit into the header correctly and I had to fix it with pliers.
  5. Put in the manifold studs and finger tighten them after you have coated the threads with the anti-seize compound.
  6. Tighten the manifold bolts from the center out.
  7. Tighten the EGR nut. Again watch the tube and make sure it fits completely inside the header.
  8. Install the O2 sensor after coating it with anti-seize compound. The wiring harness on the sensor makes it hard to twist so try to keep the harness from getting tangled in anything. When you get the sensor as tight as you can with your fingers finish the job with the channel locks and use as much pressure as you did you remove it which is not very much.
  9. This point is the best time to slip your modified transmission dipstick tube back into place and remount it with the 10mm nut. It is a lot harder to do once the crossover is in place. Having the engine tilted forward helps you to reach the mounting spot.
  10. Remove your blocks and the parking brake and set the engine back to resting position.

The next part to install is the front header.

  1. Drop header openings up in front of the engine and align it on the end studs.
  2. Start the first and last manifold nuts but leave a little play in them.
  3. Put in manifold studs after coating the threads in anti seize compound. Leave play in them also.

The most frustrating part of installing the headers is the crossover pipe. The crossover bolts are 9/16 14mm

  1. Put the metal donut gaskets in place and set the crossover in position.
  2. In each flange use the bolts with a big washer on each side and a lock washer on one side.
  3. Start all four bolts loosely. I started with the front bolts. I did the rear flange bolts by fishing the bolt through to the front so that the nut was in my sight while I was trying to put it on.
  4. Once you get all four crossover bolts in place you can tighten the front header from the center out.
  5. Tighten the front crossover bolts but do not torque them down at this time.
  6. The rear flange must be rotated to a certain angle see picture to reach the bolts from under the car. To tighten these bolts you need somebody to hold a wrench or leave a wrench or ratchet on the bolts while you tighten them from underneath.
  7. Jack the car up and set on jack stands. Use the right combination of extensions and your swivel socket to tighten the rear crossover nuts from underneath. Torque these down and set the car down.
  8. After the car is on level ground torque the front crossover bolts.

Your headers are finished now replace the items you took off.

  1. Replace the items that were removed during the steps.
  2. Replace anything that you needed to remove that I did not list.
  3. Replace the items removed for working room before the install procedure.
  4. I had one nut left over. I found that it was from the stock front manifolds heat shield.


For this part you need to have the car jacked up as far as you can get it. Make sure to support the car with jack stands.

  1. Use the bolts that came with the headers along with big washers on each side and the lock washer on one side and mount the flex pipe to the rear header pipe. The easiest way to start is to stick the bolt through the back so you can see the nut as you try and start it. It is tricky to keep your gasket GM part 12565634 - closed end towards engine open end towards rear lined up as you try and start the nuts on each side because the holes for on the rear header and the flex pipe are so large.. It proved to be quite difficult for me. An extra pair of hands at this point would have saved me quite a bit of frustration. When you get the bolts started make sure that your gasket is nice and centered as you finger tighten the bolts.
  2. Use a 9/16 box end wrench to hold the other side and ratchet the nuts tight. Still keep an eye on your gasket to make sure it is lined up because it is still visible to you at this point.
  3. Use your putty knife to scrape the old gasket remnants off of your catback system.
  4. Install the O2 sensor use anti-seize using channel locks.
  5. You will notice when you try and slip your R/T cat on to your flex pipe that they do not slip at all they just butt up against each other. If you decide to install the pipe yourself you should support the weight of it by using a small box when you proceed with the steps.
  6. Use the stock 15mm nuts coat with anti-seize and your new gasket GM part 10328740 - thick ring pointing away from cat and bolt the R/T pipe to your cat back system. Remember this gasket is 2.5. I assume you are connecting to a stock cat back. Tighten the nuts fully use anti-seize and reconnect the passenger side rubber hanger and then the driver side rubber hanger. It is nearly impossible to do in the other order.
  7. If you plan on welding this pipe yourself or have it installed at a shop disregard this step. Use the 3 plumbers clamp to seal up the gap between your flex pipe and the cat pipe. Make sure you take the rubber part out. Using this clamp I was able to seal the exhaust leak to a minor tick.
  8. Now you must either weld the flex pipe to the R/T cat pipe or drive to a local exhaust shop and have them weld it. If you do the latter I recommend you have them inspect for leaks while they are under the car. If you have a welder and the skill to weld I doubt I need to tell you how to do it. There will be no harm in driving the car to the exhaust shop without a pipe connected but it will be very loud.


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