Last week, I decided I wanted to spruce up the interior of my car a bit. How I could do that…well, I could get a set of floor mats, I could replace the shift knob and boot (they’re both worn out), or I could do something for functionality and form – add some more gauges. I looked through what’s available, and made a list of everything I want…air:fuel ratio, intake manifold pressure (vacuum/boost), battery voltage, and oil pressure. That’s four gauges – a slight problem, because the largest A-pillar gauge pods out there are 3-gauge pods. That leaves me with two options – get a mounting cup and stick it on either the dash or the steering column, or get creative.
If you ask me, the cup would’ve looked stupid – that’s for muscle cars, not tuner cars. However, I vaguely remember seeing a full-race RSX with a gauge mounted in the driver side center air vent, which I thought was a pretty cool way to make use of that, so I decided to go that route. Now, the question is, which gauges should go in the pod, and which one should go in place of the vent…well, I’m going to want the ones that I have to look at frequently while driving to be easy to look at. Oil pressure and battery voltage are something I want to know, but it’s not like the voltage is going to significantly change while I’m driving, and if the oil pressure has a major change while I’m out redlining it, chances are the motor’s already blown.
That leaves air:fuel ratio, and intake manifold pressure – two things that will definitely change frequently while driving. I don’t want a huge project on my hands, so I’m only going to do one gauge – I don’t want a gauge pod with empty spots in it, so that means I’m definitely going to be mounting whatever I get in the dashboard air vent. The air:fuel ratio gauge will require removing my ECU’s secondary oxygen sensor and replacing it with one that goes directly to the gauge, so I need K-Pro before I can do that if I want the car to remain running properly, so that leaves the manifold pressure gauge. That’s fine with me, that gauge is useful for keeping track of my fuel economy as well.
The gauge I’d seen mounted in that vent was pretty much a perfect fit, or at least that’s the way it looked – so I measured the vent, three inches in diameter. Well, the only 3″ MAP (manifold absolute pressure) gauge that goes below 0PSI that I can find is the DEFI Boost Gauge…in fact, the only 3″ gauges I can find period are the 3 1/8″ DEFI gauges. They certainly do look pretty sweet, but at $300 each, I really don’t think so…eventually I’ll replace my MAP gauge with the DEFI Boost Gauge, but I’m not looking to spend a ton of money right now.
That leaves me to look at the other ones I can find at the next size down – 2 1/16 inches. ClubRSX has some pretty sweet ones, but all the local stores (Pep Boys, Autozone, Advance Auto Parts) have these SunPro gauges – and the MAP gauge is between $20 and $30, depending on where I go. They don’t look as nice as the ones over on ClubRSX, but the price is right…and I’ll put a nicer one in later on. I wanted some instant gratification. So I picked it up, came home, and hooked it up.
The previous mods I’ve done (namely the stereo and oil catch can) made getting this gauge hooked up much easier. The gauge didn’t just pull a digital reading from the MAP sensor, which would probably be doing by pigtailing off of the ECU’s MAP sensor connector – rather, it came with a real thin hose that literally just hooks up to the intake manifold and has its pressure actuate the gauge. So there were two key things that I needed to make this thing work – a hookup to the manifold, and a way through the firewall.
The hose connecting to the intake manifold and going through the firewall
A way through the firewall was easy – the power cable going from the battery to my amp and subs already goes through the firewall, so I just jammed the hose through there and reached through the engine bay to pull it through. The way to the intake manifold hookup was also already paved for me – the gauge came with a little threaded brass fitting to connect the hose to the manifold. The outer diameter of this thread was about 5/16″…well, the PCV valve is about the same size. I already had the PCV port on the intake manifold plugged with a little vacuum cap, and I had a foot of 5/16″ vacuum hose lying around, both as a result of building and installing my breather tank a few weeks ago.
So I got the hose hooked up to the intake manifold, run through the firewall, and hooked up to the gauge right there in front of me…sitting in my cupholder, with the backlight wiring hooked up to a 9V battery so I could read it at night. It stayed that way for a couple days while I devised a game plan to get it mounted in the vent.
What I came up with was to fabricate a circular fitting out of sheet plastic, with a 2″ diameter hole in the center to hold the gauge. I took a ride down to Home Depot and failed to find anything myself, so I asked an employee there – they suggested plexiglass. I picked up a little piece (8″ by 10″) of Lexan XL10 .093 thickness (not sure on the units, inches seem likely based on how thick it was by the eyeball though) transparent plexiglass, figuring I’d spray paint it flat black so it vaguely resembles the air vent it’s replacing.
Drawing and cutting out the stencil for the gauge mount
First I had to get the outer circle cut out. I removed the climate control unit from the car, and used the vent on that as a stencil to draw a circle (basically just a 3″ diameter circle) on a sheet of paper, taped the paper to the sheet of plexiglass, and used a box cutter to cut out the circle – the goal here being to scratch the stencil into the plexiglass. With that done, I needed to cut out the square section of plexiglass that the stencil was scratched into. This was a bit on the difficult side. First I tried a table saw – this didn’t work out too well; the plexiglass is too rigid and ended up almost taking my fingers off.
Success ended up coming with a fine-toothed hand saw. It was a pretty long process getting it cut out, but it worked eventually. After I had the square cut out, I used a table grinder to take it down to the circle, being careful to leave about 1/8″ of extra plexiglass around the outside of the whole thing just in case – this ended up being a good idea, so if you do this yourself, make sure to do that.
A couple holes drilled...
...and the whole center portion is gone
This left me with the question of how to get the 2″ center cut out. The outer part had to remain intact, so that ruled out any kind of saw – most power tools. The first thing I did was to basically do the same stencil process as the larger circle – I traced the gauge’s face onto a sheet of paper, taped that to the circular piece of plexiglass (doing the best I could to make sure it was centered), and cut that out with the box cutter – making sure to scratch it into the same side as the larger circle. Then I took a small (1/8″) drillbit and started drilling holes around the smaller circle – again, leaving about 1/8″ of extra plexiglass around the inside of the whole thing. The holes were very closely spaced, something around 1/16″.
Once I had all the holes drilled, I used the drill as a makeshift saw, cutting away the small gaps between the holes. Once all the holes were out, I put the newly-fabricated mount up against the back of the gauge (the idea being to push the gauge in back-first, so that the front would sit in the mount) to see how much larger the hole needed to be. I used the drill to bore away any of the larger portions that were still intruding upon the gauge’s space, checking periodically to see how much more clearance I needed, then once I got pretty close, I switched to sandpaper. The coarser the better – I had some 150 grit lying around so I used that, but something lower would’ve gotten the job done quicker.
The gauge in its mount
Eventually I had the hole sanded out to the point that the gauge would fit. Now it was time to get it to its nice snug fit in the vent hole in the climate control unit assembly. Basically the same process as getting it to fit the gauge – check fitment, sand away some excess, rinse, repeat. It is worth noting that the mount needed to be slightly off from perfectly circular – the part going at the bottom of the assembly had to be cut inward a little bit; the outer shape was still convex, but basically that side of the circle had to be flattened out a bit.
This took literally hours of sanding – I would’ve been easier if I’d just used the table grinder from before, but first of all it wasn’t my table grinder and I would’ve needed to borrow it again, and second of all I was worried about taking off too much and ruining this little piece of plexiglass that I’d just spent several hours shaping.
Scuffed up the gauge mount for painting
Once this was fitting in nice and snug, I scuffed up (using the same 150 grit sandpaper) the surface of the side that would be facing out of the dashboard toward me to prepare it for painting. I chose the side that didn’t have the scratch marks from the box cutter – realistically it probably wouldn’t show through the paint, especially after scuffing it down with the sandpaper, but whatever, might as well take this little step to make sure it looks good.
RUST-OLEUM, KING OF THE PAINT
Now, I was going to spray it flat black to match the vents (like I mentioned earlier in the article), but as I was getting ready to go spray it, I noticed I had some glossy deep(ish) red spray lying around that I’d used on the barbeque. I looked at the barbeque, and then at the panels to the left of the steering wheel, which were already painted red when I bought the car, and noticed that they were pretty close in color. So I decided to go with the red. I put down a couple paper towels on the picnic table, set the mount on it, and sprayed on a real thin coat of the red paint. After giving it a couple hours (this Rust-Oleum paint from Wal Mart claimed a two-hour cure time) I sprayed on a second thin coat – this made it nice and smooth.
The mount, sprayed red and mounted in the CCU
I let this sit all night – mostly because it was late and I was tired. When I got up the next day, I got some duct tape, made a 4″ square (roughly, I just eyeballed it) of duct tape and used it to cover the now-open hole in the heating system that’s sitting right behind my MAP gauge, and would otherwise be blowing hot/cold air at it. Once I was satisfied with how well this was done – probably not perfectly, mind you, as there’s some foam on the underside of the pipe, presumably to keep too much heat from hitting the back of the head unit – I stuck the gauge in the mount, with its face on the red-sprayed side, stuck the mount in the CCU with the gauge face on the same side as the knobs (obviously), and used some more duct tape to get it held in there nice and tight, being careful not to let any come around to the portion that would be visible.
The hose (white) coming through the firewall next to my amplifier's power cable (red)
Then I took the CCU back out to the car, pulled the little vacuum hose up from the hole in the firewall down by the pedals (making sure to run it behind the pedals) up through the little access areas down there (near the OBD-II connector), behind the head unit, and finally up into the CCU’s area. Trust me when I say I’ve made it sound much more complicated than it really is. I connected the hose to the back of the gauge, connected the CCU’s plug, and stuck the whole thing back into the car.
Mounted in the CCU, before reinstalling the head unit
While I had the head unit and CCU out I also did the wiring for the backlight – since I want it to turn on when the headlights come on, I spliced one wire into the head unit’s illumination circuit, and the other into the head unit’s ground connection. Again, since I already had an aftermarket head unit in, it was easy, because of the Honda wire harness being spliced to the Alpine wire harness. It’s also worth noting that it doesn’t really matter which backlight wire I connected to which head unit wire – it’s just an incandescent bulb, it doesn’t care which direction the electrons are flowing, as long as they’ve got a circuit.
Ziptie to secure the intake manifold hose
Then I went under the hood and ziptied the new vacuum hose that’s now connected to the intake manifold’s PCV port in such a way that it wouldn’t bend so far that it kinks and seals – otherwise the gauge wouldn’t get proper readings and I might have issues with the braking system and whatnot. Certainly not something I’m interested in.
The finished product
All in all I’d say it turned out pretty well. It was a lot more involved than I’d originally intended, but it does look pretty sweet, and having a gauge showing the intake manifold pressure is helpful when hypermiling – specifically, the technique known as “driving with load” (scroll down, it’s #56). Since installing it I’ve seen a decent improvement in my mileage, as a result of having that information available to me.