RX-7 Boost Gauge Installation

This document details the installation of my Autometer 3301 Boost/Vacuum gauge using an A-Pillar mount, into a third generation RX-7.

Necessary Items:

• Coat Hanger
• Electrical Tape
• Nylon cable-ties
• Boost Gauge
• Miscellaneous hardware that comes with Boost Gauge (nylon tubing, brass fittings, etc.)
• Coat Hanger to route boost gauge tubing
• Short length of rubber tubing which just fits tightly over nylon tubing
• A-Pillar mount
• Alcohol, or some other cleaning agent for A-pillar

• Approximately 5 feet of light-duty dual-strand wire
• Either nylon wire splicers, solder, or some other way of splicing wires together

I've had a lot of problems with my car producing sufficient boost (as of this writing, I still am). I needed another diagnostic tool to be able to tell what the turbos were actually doing, to further determine where my (relatively) low-power problems were coming from.

After taking my car to the dynamometer, and registering only 193 peak hp, I knew something was wrong, but needed further information. Thus, I decided it was time to have a real-time indication of how much boost the car was actually producing.

This, I feel, is one of the few serious omissions in the car's design, the lack of a boost gauge. Unfortunatly, not only does Mazda not provide a boost gauge in the car, but they do not provide any "official" guidelines for the performance of the turbos. Generally speaking, net wisdom prescribes the following behaviour for the sequential turbo setup on a third-generation car, when they're working properly.

• On wide-open-throttle (WOT) boost should go up to 10-11 psi
• At approximately 4500 rpms, boost should drop down to 6-7 psi
• After the drop, boost should again rapidly recover to either 8 or 10 psi (depending on which version of the ECU is installed in the car. Early 1993 cars will hold 10 psi of boost until redline, while later versions hold slightly less, around 8 psi).

After having determined the need for a boost gauge, I selected the Autometer 3301 boost gauge for the following reasons:

• It cost around $50
• It was lit
• It had a black face, white numbers, and a red needle, with a silver ring around the face (This was my attempt to add a relatively stock-looking instrument to my dashboard.)
• It was a 'full-sweep' gauge, registering almost 270 degrees of travel
• It showed both boost and vacuum

Then, I needed to select an appropriate mounting method. I ended up choosing an A-pillar mount, designed specifically for the third-generation RX-7. (The other easily-available alternative, the steering-column mount, is generally more expensive, and I feel it gets in the way of seeing the all-important tachometer.)

I bought my Boost Gauge from Summit Racing and my A-pillar mount from Diamond Star Specialties. (Note: DSS is actually a Mitsubishi parts dealer, but they have some things for RX-7s as well, one of which is the somewhat-hard-to-come-by RX-7-specific A-pillar mount. This combination of items works very pretty well together. The gauge fits exactly in the slot, and the A-pillar mount follows the contour of the A-pillar very closely (although the texture of the mount does not exactly match the texture of the original A-pillar.)

Some additional points to note: At night, the boost gauge can sometimes cast a reflection on the inside of the highly-sloped windshield. This is but a mild annoyance. Secondly, the light on the Autometer gauge is significantly dimmer at a particular setting than the rest of the dashboard lights, again, something which (for me, anyway) was easily overlooked.

References to "left" and "right" are as you are looking at the steering wheel as you would normally while driving.

Step 1: Route nylon tubing through firewall
I found it much easier to route the nylon tubing from the driver's side footwell, through the steering wheel boot. This made it possible to keep the tubing relatively short, and avoid drilling holes through the already-crowded firewall. Poke a hole in the steering wheel boot with a coat hanger, and then stick the coat hanger all the way through, at a slightly upward angle. The steering wheel boot is a double-boot, that is, you'll be going through the surface on the passenger compartment side, and then out through the boot on the engine compartment side. Look for the tip of the coat hanger in the engine compartment near the steering wheel column.

Then, slip the tip of the nylon tubing over the end of the coat hanger, and pull it back through into the passenger compartment. You should now have a piece of nylon tubing with ends on either side of the firewall.

Step 2: Connect nylon tubing to intake plenum
On the passenger's side of the intake plenum (the silver thingy in the engine compartment with 'tubes' molded into it), there'll be a small (1/2" inch) rubber cap over an unused tap into the intake manifold. Remove the rubber cap (it just pulls off, but it can be a bit stubborn if it's never been removed), and attach the short length of thin rubber tubing. Slip the other end of this rubber tubing over the end of the nylon tubing, making sure that you have a tight seal. (You may want to use some RTV to aid in this process, just be careful not to use too much, in case you ever want to remove this.) Route the nylon tubing as you wish through the engine compartment. (I went straight back from the attachment point, along the firewall, zip-tying to various brackets, until I got to the steering wheel column, at which point I went straight down.)

Step 3: Route nylon tubing in passenger compartment
I took the easy way out here. There's a small gap between the dashboard and the A-pillar where I stuck the nylon tube, in preparation for the A-pillar mount. Then, I nylon zip-tied the tube up underneath the dashboard to get it out of the way.

Step 4 (optional): Run wiring for lighting
I used the ashtray light to power the boost gauge light. This light dims with the rest of the dash lights, and is readily accessible. This step is optional, since most people won't be looking at the boost gauge at night, but it's a nice extra feature that we may as well take advantage of. (It goes without saying that we're going to be messing with the electronics in the car here. If you don't feel confident about your abilities to keep from crossing wires, you may want to disconnect your battery, but keep in mind that this may require you to reset your radio after you're done. Otherwise, just make sure you keep your wires apart to keep from eating up fuses.

   Remove the panel around the parking brake console (and containing the rear defroster switch, security light, and ashtray). To remove this panel, first, unscrew the gear shift knob. This knob simply unscrews counterclockwise (like 25 full turns!), (if its never been off, it may be a bit tight). Then, remove the panel by simply pulling up on it. I found it easiest to just get my fingers underneath the left edge of the panel, and lifting up. (It's held on by like 5 little clips) (Note: Do not wrap your fingers around the panel through the parking brake boot, as this piece of plastic/cloth is NOT attached to this panel, and has its own frame. Pulling on that section of the boot will break the parking brake boot frame!) This will expose the underside of this panel. Be careful, as the wiring harness which goes to the lights and switches on this panel are very short. You may want to disconnect these, for easier access to the wires going to the ashtray light.
   Fish a length of light-duty dual-strand wire through the dashboard from inside the driver's side footwell to underneath the panel you just removed. I found this easiest to do by putting the coat hanger through from underneath the panel, just to the left of the shifter knob, and then poking it through until I could see it in the footwell.
   Now, splice your newly-fished wire into the two wires leading to the ashtray lights.
   Finally, run the wire up to the A-pillar mount, making use of the same gap you used to run the nylon tubing.
At this point, you should have everything done, except for installing the boost gauge itself (tubing and wiring run, etc.)

Step 5: Installing A-pillar mount
Note: When I put the A-pillar mount up to the A-pillar for fitting purposes, I didn't like how far up the pillar the mount ended up sitting. So, I cut diagonally across the bottom of the pillar (following the curve of the dashboard), so it would sit flat against the dashboard, and lower down. This worked perfectly (but this step is obviously optional.)

Run the wire (if you bothered doing the wiring) and the nylon tubing through the hole in the A-pillar mount. Hook the wires to the light bulb, and the nylon tubing to the brass fittings supplied with the 3301 gauge.

Now, clean the surface of the A-pillar mount with alcohol, or something else to remove any contaminants from the surface. Then, remove the adhesive protectors from the back of the mount, and stick it carefully to the A-pillar.

Finally, put the gauge into the hole in the mount, and enjoy your new boost gauge.

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