Installing Headers

[KP] Now that I’ve completely finished the installation of my RM Headers, I thought I’d take a minute or two to reflect on the task in the hope to provide some insight to those of you who have contemplated to do this job yourself.   

In summary, the job is not all that difficult. There’s a lot of steps, and quite a few things to take apart. However, all of this is rather straightforward… especially when you have easy access to ask Randy any questions along the way.

Working on the rear side of the engine is easy and once you have removed the stock cats and downpipes, the stock manifold is easy to remove as is the header to install. To get enough access to the front manifold, you must remove a major structural cross beam. To do this you need to remove the bolt through the rear engine mount, and then undo one 17mm nut and two 17mm bolts per side to completely drop down this crossbeam. To get enough access to get it completely out of the way, you need to undo another brace and some brake cable (emergency brake) hangers, and

 also loosen the supporting bracket for the shifter cables. You don't ever take the shifter  cables apart, you just loosen the bolts that hold the cable ends in place to give you  enough room to remove the crossmember. 

Guys, this is all straightforward, just a lot of ratcheting for those without air tools. The final step in getting access to the front manifold, is to remove the AC compressor. The compressor is attached to a supporting bracket with 4 12mm bolts. You simply remove these bolts, turn the compressor slightly to clear the belt, and then lower the compressor to sit on a block of wood or similar. Re-install of the compressor is really simple — just the inverse of the above steps. There’s never a need to mess with any belt tensioners, etc. Once this is done, access to the front manifold is easy.

Admittedly, I was worried about putting the crossmember back in place and especially in getting the 17mm engine mount bolt lined up and in position. In practice, this worry was unwarranted. I put the cross member back up in place, left all of the attaching hardware loose. This allowed me to wiggle the crossmember to the right position to slide the

 engine mount bolt into place. No problem.

All in all, it was a rewarding project. The RM headers and cat pipes are really quality products. I really wasn’t expecting all of the hand porting work on each of the header ports… very impressive.

Perhaps best of all was the access to and support of Randy whenever I needed it. Randy has quality products and a first class customer support perspective.

 If any of you are considering this installation and have any additional questions, please  private me and I'd be more than happy to respond and provide my phone number, etc.

[NM] Lessons Learned:

– Shop Manual: Not a ton of info on the headers but at least I knew what I was looking for. Also, helped me with the oil change and is really going to help me with the springs.

– Lift equipment: You will need a decent jack, some wheel chucks, and 4 jack stands. I found a great 2 1/2 ton medium duty jack at WalMart ($40) that the black top comes off (cotter pin) and then the flat round piece fits easily under my NSX. I added some groves so match the underside of the NSX too.

– Sockets: You will need 10mm, 12mm, 14mm, & 17mm sockets. Get the 6 pt kind and buy the best. It sucks to have to go to the store 100 times to buy these and a third of my install time was spent running out for more tools. Sears guarantees theirs for life

– Wrench: You will need a 22 mm wrench for the O2 sensors. I was able to get the front one off without removing the header – but that is the exception.

– Keep stuff together: When you take something off the car. Keep the nuts & parts together. Better yet, lay the parts out next to the car in a similar location as to where they are going back in.

– Ratcheting Wrench: You will need a torque wrench and a smaller hand wrench. There is a newer wrench with a handle at the bottom that lets you hold the wrench in one location and twist the bottom. Very convenient! Also, you may need a hollow bar to fit over one of your hand wrenches.

– Adapters & Extensions: You will need many different sizes of extensions and all adapters (1/2", 3/8",1/4"). The hardest part was figuring out a way to get to every nut and apply enough torque not to strip it. You will be trying a dozen angles and extensions for each one and every bolt becomes a mind teaser.

– Glasses & Gloves: Wear them. My eyes killed and my hands are raw. I personally would get some decent shop gloves and cut out the fingers. You want the knuckle protection but will need the touch of your fingers. Watch out though as many of the AL NSX stampings are very sharp!

– Liquid Wrench and Locktight: I talked to Randy and he didn’t think that you need to worry about torque settings – just make sure everything is good and tight. I used a little locktight and the liquid wrench on everything but the O2 sensors.

[LB – 00/1/3] RM Header Installation 1991 NSX

Kendall, Nick, and Spencer have all preceeded me with great write-ups so I would just like to detail my experience on my 1991 since there are some differences. I have broken this into a tools and installation section.


DO NOT EVEN THINK ABOUT USING 12 POINT SOCKETS FOR THIS JOB. Exhaust fasteners are soft and you will definately strip a few if you use them. 12mm and 14mm 6 POINT swivel sockets REALLY help. You can get them at Sears pretty cheap. If you buy a metric set of these from Sears, remember that the standard set DOES NOT come with a 14mm, so get that in addition to the set. Also have on hand a 12mm 6 POINT deep socket for the manifold nuts, the swivel sockets are too shallow due to the length of the studs. Nick talked about extensions and he is right on. A really good investment is a set of 3/8 swivel extensions, these extensions have a funny looking tip that will allow the socket about a 15 degree swivel without a universal adapter. I have found that the universal adapter almost NEVER fits when you need it.

And last but not least (as Nick mentioned) GLOVES, GLOVES, GLOVES, if you do it without them you will know what we all are talking about, a lot of sharp edges under there:-(


To start with make sure you spray ALL the hardware you can get to with WD40, PBBlaster, etc. I used PBBlaster and it works very well. As Kendall points out it this job is pretty straight forward, just a lot of stuff! When I looked down at the garage floor once everything was apart I was astounded as to how many parts and fasteners I had actually taken apart.

There were a few "challanges":

The front beam is a large aluminum piece that goes the full width of the car and has the front engine mount bracket on it. Once you get all the fasteners off (two 17mm bolts, and one 17mm nut per side, plus the engine mount through bolt) it is still pretty tight. I found a little help from a hefty screwdriver/or crowbar was handy. This piece is mounted on two long studs, so it wants to come off straight, if you cock it even a little it gets stuck. Be patient. Clear the emergency brake cables from under it by shifting them above it as it comes down. Once off you have a clear shot at the AC compressor and the front manifold/downpipe. Just keep wrenching.

Assembly basically goes in the reverse order, the rear header is a breeze. The front header did present a little more thought and work. Once the front header was mounted, I went to install the front beam, the nut for the engine mount that used to be fairly accessible was pretty much hidden by the front header. You need to get your left hand BEHIND the front header (between the front header and the engine block) and reach in to hold the nut in place, then use your right hand to turn the bolt. At this point you are hugging the front beam. A pain in the butt, because you cannot see anything up there, it’s all feel. Spencer points this out in step 32, frustrating to say the least.

Now that I was done with the front beam installation I laid there and looked up, to my disappointment the front header pipe on the drivers side of the car (Cylinder #6) was so close to the engine mount bracket (1/64") I was sure it would be rattling once I started the engine, so out the front beam came AGAIN for some minor dremel work to clear this interference. I marked the location prior to removing the front beam, them dremeled it on the bench, remounted and checked, removed, dremeled a little more, remounted checked. OK. Now remember, these cars do have tolerances and the headers are mandrel bent and hand welded, so this may not be a issue for you, but make sure you look for it. There is still a lot of work to finish from here, you DO NOT want to find out AFTER you are done that you have a rattle.

So the headers are mounted, cross beam in, and it is all down hill, mmm….. I also found some close interference with the rear rod beam ("U shaped suspension bracket", ala Spencer step#1) and the front cat. The header pipe was VERY close (1/16"), almost touching(accounts for my tiny rattle at 3900 rpm). THIS WAS WITH THE STOCK EXHAUST SYSTEM ONLY (my RM was in the mail, couldn’t wait!). To solve this I shimmed the rear rod beam with washers between the rob beam and the rear beam. The spacing of a washer thickness or two will clear this nicely, no dremel needed! Again, this may not be a issue for you, but make sure you look for it. It is also not critical to do this early in the reassembly, since you can do this after you are done with your first test drive, very easy to get to. NOTE THAT WITH THE NEW RM DTM EXHAUST THIS WAS NOT A PROBLEM. THERE WAS ABOUT 3/8" CLEARANCE, NO PROBLEM.

OK, we are now ready for the last step: install the muffler/exhaust. If you look down at the parts you removed (manifolds and pipes) you will notice both front and rear pipes have a flex section(this is different from the 1995 car). The headers DO NOT have a flex section, but the flanges do rotate which really helps. The way to get this all to go together is when you mount both cats, DO NOT tighten the three nuts on the header side of both cats, only start the nuts so that both cats are hanging loose. Then wrestle the exhaust into place. I did this alone and the exhaust is very bulky and awkward, so I used a floor jack to hold it up and moved it into place, probably MUCH better with a helper. Once the flanges are all aligned tighten the whole system.

Well, job done, 10 hours total. Looks great, sounds great, feels great. I’m not sure I could get this down to Spencer’s 3 hours on the second time though. A special thanks to Kendall, Nick, and Spencer for their previous write-ups, invaluable. And a thank you to Randy, who was always there to take my calls (2) and give me some worthwhile tips.

Installing Comptech Headers

[SS] First, headers do increase power, and reduce weight. The car felt better this morning driving to work. I highly recommend them.

Second, I can relate to Nicks experiences, right down to the dream about 3 Ninjas (N, S, and X) beating you about the neck and shoulders. My shoulders are bruised and raw, my face is black, and I have several other nicks, scrapes and abrasions. A set of glasses and bandana tied around your head are very helpful. About 3/4 in to the job, I was told my bandana was too tight if I still thought this was a good idea.

Using the Nick Scale of Automotive Upgrade Installation:

Number of tools dropped on head …..1 (I am a quick learner)

 Number of stars seen.......12
 Number of calls to Randy.....0
 Number of times I wished Nick was there to help.....5
 Total Time......10 hours

Now for a few extra details about installation:

Get the shop manual, it has all the torque settings and excellent diagrams. Most of the bolts attach to aluminum threads. It is VERY easy to strip aluminum, and VERY unpleasant to fix. Do not overtighen. Do NOT spray the O2 sensors with liquid wrench. Bad things happen as other owners can testify. Spray a little liquid wrench on the nuts  which connect the cat output pipes to the muffler pipes. A breaker bar  helps significantly in loosening some of the rusted on nuts and bolts.

The rear manifold:

  1. Remove the U-shaped suspension bracket. It is the first thing you see when you get under the car. It looks like a big flat bar connecting the front motor mount cross member to the various suspension parts. You must detach the emergency brake cables from this bar.
  3. Remove the little bracket which holds the cats' O2 sensor wires. The rubber sleeves on the wire just push out of the bracket clips.
  5. Disconnect the O2 electrical connectors which are above the little bracket you just removed. These connectors are latching type, and a little lever on the connector must be pushed to get them apart. I think the front O2 connector just came unplugged, but the rear one requires first releasing the latch on the connector which holds it to a little bracket the connector is attached to. Then, push the latch which releases the connectors.
  7. Remove front cat by removing the spring bolts connecting the cat to the front down pipe. Then remove the 3 nuts which connect the cat output pipe to the muffler pipe. No need to remove the spring bolts which connect the cat to the output pipe. Remove the two cat hanger bolts, and the cat pops out.
  9. Remove the anti sway bar. Then ends are disconnected by first loosening the 17mm nut, then insert an Allen wrench into the bolt, and use a box wrench to remove the 17mm nut completely.
  11. Remove the rear cat by removing the spring bolts connecting the cat to the manifold down pipe, then remove the 3 nuts on the cat output pipe to muffler pipe flange. Wiggle the cat off the rubber hanger.
  13. Remove the suspension bracket which attaches between the lower suspension and the body beneath the trunk. This looks like a flat bar, and angles up from the suspension to the trunk.
  15. Disconnect the rear O2 sensor connector. And remove the little bracket which holds the sensor wires to the head.
  17. Remove the heat shield on the right axle CV joint
  19. Remove the heat shields surrounding the rear exhaust manifold, and wiggle the shields out.
  21. Remove the 7 nuts which attach the manifold to the head, and remove the manifold and down pipe together from the car.
  23. Place the manifold and pipe on a secure surface, and place the open end of the 22mm combo wrench on the O2 nut. Then lightly tap the box end of the wrench with a hammer and the O2 sensor comes loose. I used a 2.5 pound shop hammer, and the O2 easily came undone.
  25. Install the O2 sensor in the rear header, and install the header. Dont forget the metal head gasket. The nuts which hold the header on are more difficult to get to as the pipes are covering them. Tighten them down as best you can. Do not overtorque.
  27. Install the little O2 wire bracket that attaches to the head. Push the O2 wires' rubber sleeves back onto the bracket, and plug in the connector.
  29. Replace the CV joint heat shield.
  31. Install the trunk to suspension angle bracket.
  33. Remove the cat gasket from the original down pipe and install on the header collector flange.
       Now, on to the front manifold. 
  35. Remove the front engine mount bolt from the cross member.
  36.  You have to get at this bolt from the drivers rear tire with a swivel socket and some long rods.
           The tire has to come off the car
  37. Remove the transmission cable carrier nuts. They are 4 x 14mm. I did not remove the nuts which connect the cables to the carrier. Along with this, remove the oil pan rock shield.
  39. Remove the remaining cross member bolts. There should be one 17mm bolt on each side.
  41. Wiggle the cross member down and over to the drivers side a bit. The tranny cables prevent you from removing this member from the car, and you just need to move it a few inches to get clearance to the front manifold.
  43. Remove the front down pipe.
  45. Remove the 4 bolts attaching the A/C compressor to the engine mount. You do not need to remove the belt or hoses, just move the A/C compressor off towards the passenger side as best you can. Mine just sat there, wedged it, but you may need to rest the compressor on a block of wood or something.
  47. Disconnect the front manifold O2 sensor wire from the engine compartment. First push the little lever to release the connector from the bracket, then push the lever to release the connector halves.
  49. Pull the O2 wires out of the little carrier above the manifold. Again, the little rubber sleeves just press out of the clips.
  51. Loosen the O2 sensor by placing the open end of your 22mm on the nut, and tapping the box end with a hammer. Once loose,  just unthread the sensor to remove it.
  53. Remove manifold heat shields.
  55. Remove exhaust manifold.
  57. Install the front header. Dont forget the metal head gasket. The nuts are rather difficult here, as the pipes are bigger and cover several of the nuts. Try your best to get them tight. Do not overtorque.
  59. Install the O2 sensor into the header, attach the wires to the little carrier, and plug the connector together and on to the mount.
  61. Reattach the A/C compressor.
  63. The front engine mount nut is kept from spinning by a little tab. I had to put a little grease on the nut face to stick it in place, then wiggle the cross member back in place. Then squeeze one hand in to hold the nut and the other hand pushes and threads the engine mount bolt on. This is all tight, tricky, and frustrating, and took me a little while.
  65. Attach 2 (one on each side) of the cross-member-to-body bolts.
  67. Attach the transmission cable carrier and oil pan rock shield.
  69. Remove the down pipe cat gasket and place onto the collector flange.
  71. Install rear cat.
  73. Install anti sway bar. Use the allen wrench and box wrench to get the nut seated, the torque down the rest of the way.
  75. Install front cat.
  77. Connect O2 sensor connectors. Attach the little wire bracket, and push the rubber sleeves back on to the bracket clips.
  79. Attach the large U-shaped suspension bracket, and emergency brake cables.
  81. Test drive. Feel the power.

[KP] This was an excellent write-up from Spencer. I’d just like to add a step 22.5 for those that may use this as a cookbook to do their own install. Step 22.5 would be something like the following:


22.5 Standing on passenger side, reach down to the AC compressor from the top and disconnect the wire going to the AC clutch. This will enable the compressor to be lowered beneath the car and set on a block of wood (next step).


31.5 Reattach AC compressor wire.

Spencer, I hope you just forgot to mention this step though you actually *performed* it. Otherwise, your step 31.5 might involve a soldering iron. I’m not going to mention how I know this. 🙂

[SS] Uhhhh, yeah, add those steps regarding the compressor wire. I never saw the wire, although I know of it from other posts. My compressor never came down, it just moved over to the passenger side about 1 inch and wedged in over there, belt and  wire still attached. I think it actually went up a bit. Hopefully I  didnt do anything unpleasant. Havent tried the A/C yet.

Please note: My car is a 95T. The cats were relocated in 95 to accomodate  the T, so pre-Ts may have a different order of removing the cats,  sway bar, and suspension braces.

I think I could do it again in under 3 hours instead of 10. I would also get a 1/2 inch thick high density closed cell foam pad to lay on instead of concrete garage floor. Saves the shoulders.

Do It Yourself

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