I have moderate experience with my Miata at this point. Big items IÕve done are: roll bar, brakes pads/rotors, new soft top, Jackson racing CAI, cat back exhaust, and radiator/fans. With that being said, IÕm the type of mechanic that watches an instruction video that says something should take an hour to do and fully expect it to take 3-4 hours.
I have a Õ93 base Miata with 60k miles. A key bit of info about it for this install is that I have already done a Jackson Racing cold air intake which makes this install a bit simpler by cleaning up the engine bay area around the exhaust manifold. If you have the factory airbox, youÕll need to remove a good bit of it before starting and there are many good guides on how to do that already.
For my header installation
New parts to install
á Racing beat header
á Exhaust manifold gaskets, header/cat gasket, back of cat gasket (highly recommended, manifold gaskets are cheap enough to replace)
á Magnaflow direct fit catalytic converter (optional, good time to replace it if itÕs rusting)
á Track Dog Racing heat shield (optional, recommended to keep heat off your heater/coolant hoses
á O2 sensor (optional, recommended to replace every 60k miles)
á Motor mounts (optional, excellent time to install it with the exhaust manifold out of the car)
1. Heat Shield: Open up the hood and remove the 5 10mm bolts for the manifold cover. It should just pop right off.
2. Spray liberal amounts of penetrating oil (I used PB Blaster, everyone recommends it for this job) on the 9 exhaust manifold bolts and the O2 sensor thatÕs sticking out of the pipe
3. FROM THIS POINT ON I SUGGEST ONLY USING 6 POINT SOCKETS. YOU WILL HATE YOUR LIFE IF YOU ROUND ANY BOLT FROM THIS POINT FORWARD.
4. With that out of the way, I would wait at least 6 hours, some suggest 24 hours until you begin to work.
5. Exhaust Manifold: I used a Harbor Freight 25Ó long _Ó breaker bar WITH A SWIVEL HEAD with a 6 point impact socket for the 9 14 mm nuts. Once they were loosened a bit I was able to use a regular 3/8Ó socket wrench to get them to the end of the studs, but I left the nuts on to make sure the manifold wouldnÕt just fall off on my face while I was under the car
6. Break the lugnuts free on the driver side front wheel, jack up the car and support it with 4 jackstands, then remove the wheel. NEVER WORK UNDER A CAR SUPPORTED ONLY BY A JACK. I also removed my passenger side wheel since I am planning to do new Mazdaspeed engine mounts since it is much easier to do the driver side mount with no exhaust manifold in the way.
7. Looking through the driver side wheel well youÕll see a bracket that is attached to the front pipe with a single 12 mm long bolt that goes through a clamp and into a nut that is welded to the bracket. The other side of the bracket attaches to 2 of the 17mm transmission bellhousing bolts. I sprayed all 3 of these bolts with PB Blaster and allow them to sit for a while.
8. O2 Sensor: IÕm replacing my O2 sensor so I just cut the sensor wire right above the sensor and unplugged it. Considering itÕs only $25 for a replacement for the 1993 single wire connector, I say itÕs worth every penny to not have to remove it while itÕs in the car. Once the whole exhaust manifold/front pipe assembly was out of the car, I used a 22mm flare nut wrench daisy chained to a box wrench to get the sucker off after liberal amounts of PB blaster.
9. Catalytic converter: Since I already had removed the old catback exhaust for a new Cobalt this past summer, I knew the 2 14mm nuts on the back of the cat would pop right off with a 14mm flare nut wrench. I then PB blasted the front 2 nuts. For the front 2 I used the 14mm flare nut wrench with a box wrench daisy chained for more leverage. There isnÕt much room but you might be able to get a torque wrench in there with a socket if you donÕt have any luck with the double wrenches. One of the nuts got squeaky at the end of the stud and then wouldnÕt twist even with my breaker bar. I used my impact wrench that then snapped the stud off the cat, which I was okay with since IÕm replacing the cat assembly anyways. You can now wiggle the cat back and forth to remove it from the car.
At this point, you have 2 options: remove the 1 clamp bolt from the front pipe, or remove the 3 bolts from the exhaust manifold/front pipe attachment to just get the front pipe out. I wanted to start with the 2 17mm bellhousing bolts, but I couldnÕt access the top bolt very easily with my breaker bar as the long clamp bolt was in the way.
10. Clamp bolt: Looking through the driver wheel well, I used a long extension, a swivel, and 12mm SHORT socket (I donÕt think a deep well would have fit) to remove the clamp bolt, it didnÕt seem very tight at all. Once youÕve removed this bolt, go back up top and remove all of the exhaust manifold nuts and pull the whole exhaust manifold/front pipe assembly out of the car. You have to pull it out past the O2 sensor then sort of rotate the assembly clockwise. It took me a minute or two to figure out, but probably would have been simple with another person under the car guiding the front pipe portion past the bracket thatÕs still on the bellhousing.
Photo looking from driver side wheel well using long breaker bar, swivel, and 10mm socket to remove long clamp bolt to release exhaust manifold/front pipe assembly from transmission bracket.
11. Bellhousing bracket: ThereÕs still the bracket on the bellhousing that youÕll want to remove if youÕre doing an aftermarket header as it could rattle against your new header. Using more PB blaster, and my trusty breaker bar with a 17mm 6 point socket they came off without too much fuss. I have had a clutch job done before so that may have made them a bit easier to come out. Once you remove the bracket, reinstall the bolts. There are somewhat conflicting torque values out there as the main rule is that all 17mm bellhousing bolts be torqued to 48-65 lbft. But there is also another value that says ÒExhaust pipe clamp bolt (to bell housing)Ó should be 15-20 lbft. I didnÕt feel comfortable with 2 of the 6 transmission bolts being only torqued on at 15 lbft so I decided to split the difference at 40 lbft.
Photo looking up at transmission bellhousing bracket, note the welded nut that you remove long bolt from in step 10. Once the header is out, you can remove these 2 17mm bolts pretty easily with a breaker bar and remove the bracket, as the Racing Beat header does not use it.
Now would be the right time to replace your motor mounts if you havenÕt done them yet. The exhaust manifold makes it very difficult to get to the driver side mounting bolts otherwise. There are many other guides out there that do a relatively good job of explaining it. I have AC which makes the process a bit more difficult to get to the 3 bolts in the passenger side of the block but you can access them from the front of the car with a socket and cheater bar.
12. Put anti-seize on the 9 studs from the exhaust manifold
13. Put anti-seize on the 02 sensor threads (donÕt get any on the sensor itself) and insert the sensor into the header. I tightened it as much as I could with a daisy chained flare nut wrench.
14. Put the new exhaust manifold gaskets on the studs.
15. Put the header into the car. Like the old header removal, you have to do some acrobatics to get it into place. Put the header on the studs, making sure the water hose bracket goes back onto its stud over the header. Hand tighten the 9 nuts onto the studs.
16. Now I replaced my catalytic converter so I had to get new hardware to use there, and hand-tightened the nuts and bolts with new gaskets.
17. Torque 9 header nuts to specs (mine went on at 32 lbft).
18. Torque catalytic converter nuts to 32 lbft.
19. Hook up the battery, start it up and check for exhaust leaks.
20. Drive it a week or so to allow the nuts and bolts to heat cycle a few times and then tighten up all the bolts again to specs.