It was time to uncork the exhaust. The ND2 head has bigger exhaust valves and ports. The exhaust ports are re-worked to aid high RPM flow. I already hindered that a little by keeping the ND1 exhaust cam, but I was really killing flow with the ND1 factory header and cat.
Mazda changed the size of the exhaust runners on the OEM header for the ND2 by about 2mm according to everything I’ve read. I can’t confirm that though, I don’t have one to measure. But it seems universally agreed. So having the smaller ND1 runners matched up to the larger exhaust ports created quite the bottleneck.
So much so that the car would pull timing in the higher RPMs and on mid-range tip-in. When I pulled the manifold off I could see a thick ring of carbon around each port, showing where the exhaust was just running full speed into that lip where it transitions from the flange to the runner.
The new header has a wide open runner design that taperes down. Even if the runner itself ultimately measured the same, the entrance to it is way smoother. In fact the runner openings match the size of the gasket near perfectly. The exhaust gas will have a very easy transistion.
I also measured the openings to see how much larger the new one was, here is what I found.
A little over 5mm larger on the new header. It does taper down, but what a difference! The exhaust will have a much easier time starting its journey through the header.
The runners also take a different route to the collector.
I don’t know why that is better, but I see other aftermarket headers use the same routing so they definitely know something I do not.
Installation was fairly straight forward. Unbolt the old one and install the new one. I removed the exhaust studs from the head hoping that would give me enough room to pull out the factory header without having to the raise the engine, but it made no difference. After a few minutes of trying, I couldn’t get the old one out without more room. I’ve heard it can be done, but it wasn’t happening for me.
Raising the engine is easy though. I unbolted the one nut holding the engine mount to the subframe mount and then placed a jack under the passenger side of the oil pan with a piece of wood between them.
I didn’t have to lift it much. Just an inch or so and I was able to wiggle it out. The new header fell right into place.
Installation was easy. It all bolted up fine. The 02 sensor swapped over with no fuss and it fired up with no leaks. I used a new ring gasket where it meets the mid-pipe but reused the oem gasket at the head. It seemed to be in good shape and still held a tight seal.
After another heat cycle it turned a nice shade of purple.
There was a noticeable amount of extra heat in the engine bay since the factory heat shields were gone so I ordered up a header blanket from Track Dog Racing. I didn’t want to wrap the header, the risk of rust and cracking scared me a bit. And since they make a blanket specifically for the ND, it made sense.
Step one was install new “L” brackets on the outer most bolts. You can see one in the above photo. Then you just bolt the blanket down, hand form it to the shape of the header and then pull it out some so it’s not making contact with it. It’s not supposed to to hug the header, just create a shield.
So far so good. The car didn’t sound much different at first, but after about 60 miles the car developed a deeper tone at idle. Cruising volume is the same, but when I put my foot down the exhaust has a little more bass to it. The car has no rasp to it at all which is exactly what I wanted. The car essentially sounds the same, just with a little more low end to the sound. I like it.
Performance wise, I’m still working with Fab9 on a tune for the car. I just sent them a log with the header on it so we will see what comes back. However, I can confirm that low-mid range feels great. It pulls very well. 2nd and 3rd gear can get addictive. Obviously it’s no Hellcat, but removing the factory ND1 header definitely woke this car up a bit. Even cruising in 6th gear at 70mph on the interstate, rolling on to the throttle feels a little more torquey.
The car also doe snot pull timing up top as aggressively now. It’s not a night and day difference there, but it’s better. That should hopefully be completely dialed out soon.
Thank you for reading and I’ll see you next time!
