COLD AIR INTAKE (CAI) (Last update: 08/21/2005)

Custom Short Intake - Home built, temporary mod.

This mod is temporary... just enough to get the stock air filter box out of the way and make a lot of room for moving the HEI module and external coil to their final position on a steel plate under the VAF sensor. This mod is very simply a K&N RU-3130 filter stuck on the front of the VAF. It fits snugly over the sensor cone and works great, but it does leave the small vacuum hose that used to connect to the old air filter box with no place to connect. A small amount of filter material taped over the end of the vacuum hose should do the trick for now. This mod is also the first step to completing the custom cold air intake project, to be detailed below.

Without the air box to hold it up, the VAF now rests on two pieces of stainless steel strap bolted to the old air box mounting points. It was easy to eyeball the length and bend/twist the new brackets to the right dimensions to securely hold the VAF at its stock location.

Fabrication time: 1 hour (with proper saw, drill press, bench vise, and grinder) to cut, bend, twist, drill, and smooth the edges on the brackets.

Installation time: Less than 30 minutes to remove the stock air box, mount the VAF on the new brackets, and install the filter. Note that I removed two of the bushings from the air box and reused them so that I could also reuse the OEM bolts and nuts to hold the new brackets.

Custom Cold Air Intake (CAI) - The more permanent solution.

Normally, the installation of a CAI is a very straightforward process.... but the basic aftermarket CAI designs trouble me. So, I'm working on a custom CAI design.

For the MX-6, most CAIs place the filter below the battery. This drops the filter down into supposedly cooler air but often, in fact, places it in the very warm outflow of air from the radiator fans... Which will defeat the purposes of the "C" in CAI. So, I'm planning to design a ducted and thermal wrapped filter "can" that will prevent warm air spilling from the radiator fans from entering the filter, conductive/convective heat transfer, and allow the filter to ingest "cold-er" air with a bit of a ram effect through the lower lip next to the fog light while still protecting it from puddle splash.

In addition, I'll be using Outlaw phenolic resin spacers at the thottle body and Thermo-Tec heat wrap to isolate the CAI tubing from radiant and conductive heat.

I would like assistance from someone who understands the operation and engineering behind the Mazda Variable Resonance Intake System (VRIS), understands the physics of "tuned" intakes, and can help with determining the best design dimensions for a CAI that will compliment the existing VRIS valve timing.

The trip wire for this question is the AEM V2 series CAIs which claim to use a dual tube system to "tune" the intake at two fixed peak resonance points in the RPM curve. Well, that is precisely the function of the VRIS (which already does this function with FOUR peak resonance points!), but it's now obvious from the AEM description that modifying the intake with even a "standard" CAI might have some effect on the intake resonance over the stock configuration (for which the VRIS is already "tuned" to).

The three VRIS valve switch points at 3250, 4250, and 6250 RPM are shown in this diagram copied from the mechanics manual, but they are also pretty easily picked out on the dyno plots.

Anyone that can help with this engineering design problem, is welcome to contact me via the guestbook, or private message on MX6.com or ProbeTalk.