NC Custom Intake, Learn from my mistakes (STR Class Legal) by auto-X-er

7 minute read

NC Custom Intake, Learn from my mistakes (STR Class Legal)

Compliments of auto-X-er @ www.miata.net

I thought that this would be best here since it is NC specific, but it also has broader uses if mods feel that it could be better elsewhere.

I am entering STR class (autocross) like many of the NC owners and was faced with the situation of not being able to use any of the off-the-shelf complete intakes. After throwing around a lot of ideas, I came to making a custom one out of Spectre Parts with a K&N Filter. Spectre makes a bunch of modular parts that allows you to make a CAI for a lot of cars and it will work for ours. This solution will cost you in the $200-$250 range. Saving over many of the other options anyways. I had a lot of hiccups with it, but now that its done I wanted to share for anyone else interested to save them the trouble. This was done for an NC1.

Bill of Materials:

1Spectre 9405MAF Sensor Adapter

1Spectre 942922° Bend Tube

1Spectre 942424" Tube

1Spectre 949990° Bend Tube

1Spectre 879190° Bend Coupler

[Can get the following at Amazon]

1Spectre 8711Adpater for Return

4Spectre 8771Straight Couplers

1K&N RE-0910Air Filter

1Spectre 8703T Clamp

1Spectre 8701Mounting Kit

I listed everything from Amazon cause they have pretty good deals on what they have. The rest you will have to get somewhere else. I order from Tognottis, cause they ending up being the cheapest that I found, but others would probably be quicker about shipping and such. Should put you right at 200 mark. Here is a picture of all the parts:

Take off the Bumper, you can follow my other Bumper DIY

Remove the bolt and 2 snaps of the snorkel:

It will slide out then:

Remove the two nuts on the filter housing:

Slide out the PCV return on the intake with the blue snap and move the tube out of the way.

Next carefully remove the MAF sensor. This device is fragile, I suggest take it out and the connector off and keep it safe in a bag.

Now, slide the tube off the housing and the throttle body. Once its off its easier to slide off that thing (whatever it is) off of the tube.

Next I recommend starting up a partial assembly. For the Spectre housing adapter use the middled sized sleeve. This is 63mm and matches the diameter that the MAF sensor is mounted at stock. Using some Vaseline or some kind of grease will make getting things together a lot easier. The sleeve is difficult with the couplers. Use the adapter I pictured for our MAF.

Now the fun part. You will need to cut the 24" tube into two sections. One off the throttle body and one to the filter. You can look ahead to understand. For my application I cut 10" from the throttle body and 5 1/2" to the filter. Its probably best to measure for yourself. Make sure to use a guide to cut evenly and clean up with a file. Make sure all of the filings are out of the tube. Aluminum fillings going into the engine would be quite bad for it. 

As part of measuring for the tube lengths attach the rubber 90° bend coupler to the throttle body. The Spectre 90° bend tube is too big to fit in that area, so I used the rubber one. If you want to have smoother flow you could make the aluminum work (so would need 2 of them), but you would have to trim it.

Next, see where the 10" tube will fit from coupler. Don't insert it too far or it will block the flow. It's best to mark it with the pieces off the car so you know the limit. After you see where the tube will sit you will need to drill a 7/8" hole for the PCV return. This shows the kits gasket and replacement piece:

Thats all needed from the kit. It comes with a bit to drill the 7/8" hole, but mine broke when I tried to use it. Perhaps it was not intended for aluminum. I ending up going to harbor freight and buying a heavy duty auger pit to not take any chances. Drill the hole is difficult, if you have a press use it. Once its drilled put the rubber piece in. I used a little bit of silicone rubber to make sure it seals well. Now you can start putting it all together as shown:

As you can see I used the t-clamp and mounting hardware to mount the that thing that was on the stock tube.

Install the MAF sensor in the housing and connect more together

The Filter I selected it the MAXIMUM size you could possible get unless the filter is much skinner like the beat CAI. It just barely slides into place:

Few more pictures of how it all goes together:

I couldn't figure out a way to fasten it down (the filter is really a support how I did it). I ended up using a thin wire between the two holes here but forgot to take a picture. Ghetto solution, but it seemed to work and no one can see it.

Should be done now. I put some silicone rubber on the PCV valve once I could let the car sit for a day to make sure it stayed on. The blue snap will not work with it. It seems to stay on its own, but I did that for good measure.

Now for me I have not gotten an emissions code thrown, but the car does idle very rough while its cold. Don't know why, seems to work fine everywhere else. Can't say I notice much of a power difference, but it does sound a lot better now 

I hope that helps others. Sorry for the lengthyness and all the pictures (which I tried to compress a bunch). Figured it was worthwhile to post, but mostly for us autocrossers. Buying the off-the-shelf ones costs more, but its probably a whole lot easier.