Removing, Porting, and Re-installing V6 Exhaust Manifolds

Tools and Supplies

Removal Procedure

  1. Loosen lug nuts on passenger-side rear wheel.

  2. Disconnect negative battery lead, then positive lead. Loosen battery hold-down and remove battery. Remove plastic battery shield (Two 7mm hex-heads, one at the front corner which has to come all the way out, the other at the center rear which needs only to be loosened, since the battery shield is slotted and slides under this one)

  3. Jack up rear of car, both sides, nice and high. (You'll want to be able to slide under all the way to the rear part of the passenger compartment)

  4. Remove passenger-side rear wheel and loosen the front half of the rubber splash shield.

  5. Remove small heat shield beneath A/C compressor tension bracket.

  6. Remove catalytic converter. If yours is an OEM item, like the one on "Ole Red", it is likely held in place with clamps. You'll probably find that these clamps are pretty well rusted and you break one or both instead of loosening the nuts. No problem, as they are standard 2-1/8" clamps, and replacements are only a couple of bucks each.

    Hint: A shot of penetrating oil on each end of the "cat" will help loosen it up. You should be able to grab it and rock it loose by rotating it in place. Once it's loose, take a large (8") C-clamp and hook the outlet pipe and the passenger-side frame rail, and you will be able to flex the pipe far enough to free the cat from the inlet end (driver's side) and then twist it down far enough to clear the inlet pipe below the 'Y' pipe and jiggle the outlet end out of the pipe which runs from the cat to the muffler.

  7. Remove the big heat shield between the catalytic converter and the passenger compartment fierwall.
    Hint: Spin the fasteners on these heat shields and other parts back in finger-tight. Saves time later figuring out which darned bolts went where.

  8. Remove tension bolt from bottom A/C bracket.

  9. Now for one of the fun parts: Remove the top A/C mounting bolts. The outboard fastener is a bolt through the bracket and into the A/C compressor. This one is a real pain to get to, and the only way I found to get enough torque on it to break it loose was to take the stubby 15mm combo wrench, put the box end on the head of the bolt, and take a 17/19mm box-end wrench, grab the "claw" of open end of the combo stubby, and then apply generous force to start it out. Once it was broken free, I could get my short 1/4" drive socket on it and take it the rest of the way out. The inboard fastener is a conventional bolt/nut, and the "stubby" works fine to hold the end on the inside part of the bracket, then a regular socket will grab the end on the outside of the bracket.

    Once the top compressor bolts are loose, pivot the compressor enough to slip the belt off the compressor pulley. (It won't go anywhere much, since it's trapped under the alternator belt, being the "inside" one of the pair)
    Now, finish removing the top bolts, and hang the compressor so you don't put too much stress on the A/C coolant hoses and tubes. I found a length of 3/16" nylon cord worked fine. Tie off one end to the decklid hinge bracket, loop it around the compressor pulley, and you can easily raise or lower the compressor as needed to make room for your hands at various later stages.

  10. Remove the lower A/C bracket (tension bracket). Hint: Again, it's convenient to spin the bolts back in finger-tight so they don't get lost rolling around somewhere. (who, me?)

  11. Remove the upper A/C bracket (main mount). The three bolts which hold this in place are a real trick, especially that one which hides behind the oil pressure sensor. I found out the hard way that there is another bracket behind the A/C mount which is part of the dogbone mount. It is a very good idea to run these three bolts back in, or the engine will shift and make extra work torquing it back into place so you can realign the A/C bracket, dogbone bracket, and the engine block, all at the same time!!

  12. If yours is a pre-88 model, remove the cooling tube that runs from the trunk wall toward the coil. For all years, remove the heat shields next to the coil, plus the little bracket which holds the plug wire "loom".

  13. You are now (finally) ready to start working on the exhaust manifolds, themselves. The front manifold has a heat shield on it which is held in place by three stamped sheet-metal nuts. You'll need a deep socket to get down over the studs and to these nuts. Remove the heat shield and add it to your pile of marginally-useful metal. (Pardon the editorial comment)

    Now, soak all of the exhaust bolts and studs on both manifolds, plus those on the manifold-to-Y-pipe fittings, with penetrating oil. I used "PB Blaster", and it seemed to work fine. It helps to hit 'em all with the oil, then let it soak in for several hours, hit them again, and let them sit again. An extra evening at this point will more than make up for not breaking any of these bolts and having to pull a head off as a result!

    Once the bolts are well-soaked with penetrating oil, contort your arms and loosen them all, but don't remove them just yet. The passenger-side top bolt on the front manifold is about the worst, in terms of access. The passenger-side bottom bolt on the rear manifold is a tight squeeze next to the alternator, but you can get to it with a box-end wrench without having to pull the alternator off.

  14. Before you completely remove the manifold bolts, it's time to attack the manifold-to-Y-pipe bolts. These are held by captive nuts that are welded to the flanges on the manifolds themselves. They can be visciously stuck, as I popped the welds on the front manifold flange (just two little beads, not much meat) in the process of getting those two bolts loose. I then ended up stuck and having to cut one of the two in half with my Dremel tool and a cutoff wheel. The two on the rear manifold came out without undue effort.

  15. Remove the manifold bolts/studs, and fish the manifolds out of the car.

    It was at this point that I realized why one of the manifolds was leaking. I had thought the front was cracked at a weld, but that turned out not to have been the case. Worse, the rear manifold had two loose bolts...one backed out about 2 threads with a visible gap between it and the manifold flange, the other just barely more than finger-tight. No wonder it was leaking!!

  16. With the manifolds off and sitting in my greasy (literally) mitts, I could see that the front manifold had also been leaking, on the passenger side. That leak I'll count as due to a bad (or failed) gasket, for lack of a better diagnosis.

  17. Porting the Exhaust Manifolds

    I figured as long as I had things apart, I might as well port the exhaust manifolds to remove those GM-created restrictions where the stub pipes from the head meet the runners. My approach was to do as much the easy way as possible, then finish off by hand as needed.

    1. In order to minimize any warpage of the manifolds while the welder is at work, I found a scrap of 1/2" x 3" aluminum bar stock from the machine shop at work and drilled it to match the hole pattern in the flanges. You'll find that the manifolds will bolt up back-to-back against opposite sides of the bar, so you only have to drill one set of six holes and you can bolt them both up simultaneously.

    2. Next, take the manifolds to your favorite welding shop and have them beef up the welds at the junctions between the stub tubes and the runners. Make sure you tell them it's all stainless steel and they should use stainless steel welding wire/rod to match. The welding job cost me the princely sum of $25 at a shop that our machinist at work recommended, so it won't exactly break the bank.

    3. Now, the easy way to do most of the porting work is to take each manifold, clamp it in a vise with some flat plates between the vise jaws and the flanges (to hold it all nice and square), and run a 7/8" milling cutter vertically down inside each of the two straight stub tubes on each manifold. The I.D. of the stub tubes is a little over an inch, but neither my machinist buddy nor I thought it was a good idea to risk shaving anything off the inside of the stub tubes by using the biggest cutter that would barely fit. As it is, that cleans out probably 3/4 of the restriction, which greatly reduces the amount of hand work in the next step.

    4. Finally, take a die grinder with a stone on it, or even your Dremel if you're a glutton for punishment, and finish grinding out the leftover bits of the restrictions so there's a nice clean path all the way through into the runners.

    5. Putting it All Back Together

      1. Start off by doing some preparatory work...make sure all the leftover gasket material is removed from the head on the rear side and from the wonderful leak-creating heat shield on the front side. Clean up the mating surfaces with some fine emery cloth.

      2. Take your new manifold gaskets, and tie them to the exhaust flanges with some heavy thread by passing the thread through three of the bolt holes in the flanges and gaskets. Leave the knots out where you can get to them later, and be sure to pick three holes on each manifold which allow you fairly easy access once they're loosely back in place.

      3. Remember to coat each of the manifold/head and manifold/Y-pipe bolts with anti-seize compound before installing them. You do not want to have to fight them if you ever have to repeat this job!

        When you're ready to reattach the front manifold, work some of the Permatex Copper between the heat shield and the head. There is nothing else, other than blind faith, forming a seal at this metal-to-metal joint. You'll have to work fairly quickly now when reattaching the rear manifold, so as not to let the Permatex set up before it's bolted home.

        Now, for the trick with the thread...it will hold the gaskets in place while you find the holes and get the bolts started. Once the bolts are well-started, but while there's still a gap between them and the manifold flanges, cut the threads and pull them out so you don't leave something in there to burn out and cause a leak.
        Tighten up the bolts holding the manifold to the head.

      4. Re-install the rear manifold in the same way (minus the Permatex, since there's no heat shield involved here).

      5. Now reattach the manifolds to the Y-pipe. It will pay to get both bolts on each manifold started before you tighten any of them down, or you'll have to torque the Y-pipe into place on the second manifold. Tighten them up uniformly, making sure that the pair on each joint are brought up tight a bit at a time, alternating between them in the process.

      6. Re-install the A/C bracket, and hang the A/C compressor back in place. You'll find it's just as much fun getting that outboard bolt back into place as it was getting it out in the first place.

      7. Now would be a great time to do the easiest oil change you've ever done on your Fiero. No reaching around the cat, no worrying about spilling oil on the cat anc smogging the neighborhood when you restart the car.

      8. Tension the A/C belt (use a tension gauge to be sure you've got it right) and tighten the tension bolt at the bottom bracket, then snug up the upper bolts good and tight. A long screwdriver (bad use of tools, sorry!) or a small pry-bar is ideal for tensioning the A/C belt. GM actually did something right on this one, and put three holes in the bottom part of the tension bracket so you can pry between them and the tab on the bottom of the A/C compressor which holds the tension bolt.

      9. Put the big heat shield back in place, and you're ready to re-install the catalytic converter.

        Take the exhaust clamps out of their boxes, and loosely assemble the clamp bars and nuts, then hang the clamps on the end of the 'Y' pipe and the inlet to the pipe that runs from the cat to the muffler.

        I thought that a bit of anti-seize on each end would make it easier to maneuver the cat back into place. However, this also makes it easier for exhaust pressure to blow the inlet end of the cat off the Y pipe if the clamps aren't tight enough!! (Hmmm...how does he know that???) It is a bit of a trick to hold the cat and the pipes snug while you tighten the exhaust clamps, but it can be done single-handedly. (I was doing that part while my son had homework to do, so I was minus my usual helper) Tighten the clamps thoroughly.

      10. Re-install that small heat shield under the A/C tension bracket

      11. You're in the home stretch now...put the cooling tube back on, pointed at the coil, and reassemble the heat shields and that loom holder on the rear side of the engine.

      12. Put the battery shield back in place, but be careful not to over-tighten the screws, or you'll crack the plastic.

      13. Bolt the battery back in place, and connect the battery leads.

      14. You're ready to crank it up...call me paranoid, but I make sure I have my fire extinguisher handy any time I first start Ole Red after a major repair. This time, all I saw were a few wisps of smoke as the solvents in the anti-seize burned off, and any leftover penetrating oil did likewise.

      15. Assuming all is well, reattach the rubber splash shield, put the passenger side rear wheel back in place, grab your jack and pull out the jack stands, then set the car gently back on its feet. Tighten up the lug nuts and you're ready for a drive!

      16. Man, this car is quiet now...I hadn't realized just how much of the under-hood noise was coming from those manifold leaks. It will take a bit more driving to figure out whether the porting operation really makes a perceptible change, or not, but time will tell. It'll also be nice to go back to the state inspector and say "yup, I fixed it like you told me to...no more exhaust leaks to worry about."