A closer look at the stock 2006 NC header
I removed the stock header on the NC the other day and took some pics of the “squid”.
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On the internetz this piece is considered to be the most restrictive and badly designed part on the whole car. I partly agree but I also understand some of the challenges Mazda engineers had when it was designed;
- Cramped space
- Pre CAT needed to meet emission requirement in all markets including California
- noise
- mass production AND low cost.
At first glance the pinched runners looks to be the main restriction:
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But from above you can see that the runner are pressformed into a square on the inside which means the volume of the runner is not that compromised as it looks.
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<div class="separator" style="clear: both; text-align: center;"></div>The obvious restriction in the header is the CAT but also the cramped “collector” that houses the O2 sensor:
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</div><div class="separator" style="clear: both; text-align: center;"></div>It narrows down to about 2”/50mm and are shaped around the O2 bung. I wonder if this is to optimize the O2 sensor reading or optimize flow into the CAT. For a comparison look how Porche did it on the 996 turbo exhaust. Turbo is dumping exhaust from the turbine directly into the CAT via 4” opening:
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The CAT outlet seems very good and has a smooth transition into a 2.5 exit. It is also smooth on the inside with no edges.
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Runner flange looks good with a taper from the gasket ID to 38 mm ID runners.
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Any serious performance tuning on the NC will involve replacing the stock header. I will recommend swapping it for the Racing Beat header or the NOPRO header if money is no object.
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