RCME style custom cone intake
I’ve had quite a few requests for information on exactly how I did my cone intake, or more commonly called cold air intake or CAI for those that like acronyms, so here are the details. Those of you that come here new to this idea may wonder why you would want to do this to your car. It has two benefits, performance and economy. Any time you allow your engine to breathe more freely you increase both performance and economy. The economy part is subject to driving habits as well but if you can keep your right foot from using the new found power that you will feel you will get better gas mileage. Another part of the economy factor is that this is a very inexpensive performance modification that also gives you a chance to show off your fabrication skills and start with a rather easy project. Why isn’t it done like this from the factory if it has benefits? Mainly because of noise. When you free up the intake or exhaust side you will get some increased noise. How much more noise depends on a lot of factors. In the case of a supercharged engine like my GTP the whine of the supercharger becomes much more audible with the stock airbox gone.
This starts as a basic ABS sewer pipe cone install that is customized quite a bit so it doesn’t look as tacky as the materials it’s actually made from would suggest. Sure, you can make one from stainless 3″ tubing that may look much nicer but it’s also a lot more expensive and that stainless tubing really soaks up heat too. This ABS duct can be made to help insulate the intake from the crossover heat by using the method here.
First, the basics. From a local hardware store get a 3″ inside diameter 45° bend elbow, typically called a street outlet. This measures ~3.5″ OD on the small end and ~4″ OD on the big end which matches up well to a 4″ flange K&N cone filter or other 4″ flange cone.
Add to this a rubber and stainless worm clamp coupler that you see in the image above, connecting the ABS pipe to the throttle body and a K&N RE-0870 4″ flange 9″ long cone.
Using this method, there are a few different K&N 4″ flange filters you could choose from as well as plenty from other manufacturers as well. I prefer K&N, I’ve been using them for at over 35 years when I first began using them on my dirt bikes. The rubber grommet to hold the IAT sensor in place is a Honda PCV grommet that you can get at most auto parts stores. Most stop there and simply assemble it all and you have a black plastic looking intake tube and black absorbs heat.
I also use an ABS coupler for the same size pipe which has a 4″ OD like the big end of the 45° bend and a small length of 3″ inside diameter ABS pipe and, of course, you’ll need some ABS cement to assemble these pieces. All of this plumbing will be found in the same area at some place like Home Depot or Lowe’s. The 3″ ID pipe isn’t shown below but the coupler and 45° bend street outlet are.
Ignore the way the image here might make it appear how they would be assembled, it’s merely showing those two pieces. The point of the extra pieces is to extend the filter into the corner of the engine bay and into an area where the air tends to be cooler and this also lines up the filter in the direct path for those that like to pull the headlight out at the track. I don’t typically do that, but I did notice the path is very good. Even if you don’t pull the headlight the air in this area will be cooler just from airflow anyway. My sole motivation for doing this was to make this really cheap intake the best it could be without getting too complicated.
To start assembling this you need the ABS 45° bend and ABS coupler above and then a short cut of the ABS 3″ ID pipe. I make this cut piece of 3″ ID pipe long enough to extend into the 45° bend to the step inside and then extend at least one inch out past the end so that the ABS coupler can be glued on. The filter then attaches to that ~4″ dia. coupler end.
When assembling this, how picky you get about details will determine how good your final product looks. As you can see, the ABS 45° bend and coupler you get from the hardware store isn’t pretty. It has a lot of mold flashing on it inside and outside and molded in labeling that will clue in everyone that you’re using wastewater plumbing ABS on your car. Some brands are a lot better than others though. The first part in assembling them is putting a taper on the outside end of 3″ pipe used to connect the 45° bend to the ABS coupler. This makes it match up flush with the step inside the 45° bend. I didn’t do this on my original version that you’ll see a picture of here, and you can see the step in it, but it is tapered on the current one I am using. Is it necessary? The benefits are probably minimal at best but it keeps the flow smooth and satisfies my need for detail.
The other thing done to the 3″ ID pipe piece is to taper it on the inside diameter from one end to the other. In other words, this piece gets bored out in a tapered fashion with an increased inside diameter at the end towards the ABS coupling and the filter and only slightly increased inside diameter at the end that butts into the 45° bend. It ends up fairly thin at the big end where the ABS coupler glues on. Don’t get it too thin though or you will compromise it’s strength. It doesn’t need to be particularly strong but obviously you don’t want it to fall apart.
This process removes the normal step that would be present with just the 45° bend like most use by itself and turns it into a very gradual tapering inside the new intake duct. This process is done with a die grinder, a cheap steel rotary file bit, steady hand and some patience but it doesn’t take very long because the material removes very easily since it’s plastic.
It could also be done with a variable speed drill but using a drill is a bit cumbersome. Hopefully anyone doing this will have one because you need that and a 7/8″-1″ auger or spade bit to drill the hole for the grommet preferably. If you don’t, you can gradually dig a hole in the ABS with a jackknife and some patience because it’s fairly easy to work being plastic. Not the way I’d go about it, but it can be done for a very basic install and I’ve definitely seen them done this way although the ones I’ve noticed were done very poorly so that there would be an air leak around the grommet holding the IAT sensor.
Once this inside pipe that actually ends up being the coupler for the ABS 45° bend – ABS coupler pieces is done, you can cement it up. Be generous with the cement and do the ABS 45° bend and inside ABS pipe that you tapered first then the ABS coupler piece onto that. I also true up the ends on the ABS 45° bend and the ABS coupler piece so they butt together nicely and end up smooth. After this is all assembled set it aside to dry.
After the cement is all dry (I glue this all together a couple days before working with it) the next operation is to drill the hole for the Honda PCV grommet for the IAT. If I recall correctly without measuring this right now, the grommet you want needs to have a 1/2″ ID hole, so if you can find some other grommet with this ID that is thick enough to work with the ABS that will work as well.
You can position this where you’d like but I stick with the general stock position and keep in mind if you think you want to move it out very far you will have to extend the harness. I wouldn’t bother, any fooling with the IAT (spoofing, repositioning, etc.) is highly over-rated and except under certain circumstances it’s without benefit. (Argue with me if you must but do it in your own head and don’t bother me because I’ve played with these far too much.) 
Now you can use the rotary file bit or some coarse grit sandpaper to clean up the inside of the assembled duct of the cement and any other smoothing you want to do internally. There is a little step in the ABS coupler piece you probably want to take out of there as well. Here you can see a general idea from my first version what it will look like, peering in from the big end of the duct.
Notice how there is no air flow disrupting step on the inside at all and it has a smooth transition. Unlike in the picture above, yours will still be ugly on the outside right now because nothing has been done with that part of it. Take some coarse sandpaper and begin smoothing out the flashing, etc. and smooth the outside in preparation for primer. Don’t get too carried away and sand through the outer skin of the ABS because then you will get to the softer and more coarse inside plastic which will make it harder to get a nice finish and will create some shrinkage issues in the surface after you finish.
I should mention that before I do this I like to install the intake on the car and heat cycle the ABS because it tends to get soft the first few times it’s heated. I have also heat cycled them at 200 degrees in the oven. I cycle them 5 times at about 10-15 minutes in and then out long enough to cool completely. This is in fact another good reason to take the time to paint your new ABS duct because the black color of the ABS absorbs heat very well, not something you really want for intake air of your engine. The cooler the air the engine is taking in the more densely packed with oxygen molecules the air will be and that means more power available on a modern electronic fuel injection engine and even on many carburated engines even without jetting changes. I painted mine the Topaz Gold of my GTP because it’s a lighter color that reflects heat well and roughly matches the outside finish although it’s not exactly color-matched.
You can really tell the difference between one painted a light color and one left black when you lift the hood and touch it. My advice? Paint your duct a light color of your choosing. If you’ve got a dark color car you might want to consider a light color like a nice metallic silver with a clear coat. I’d stay away from the fake chrome paint that really looks nothing like chrome and for me white just doesn’t belong under the hood of a car even if your car is white. The finish is really where you’ll make or break this inexpensive intake and how it looks. The attention to detail on the inside is where you’ll impact how it performs.
Back to the sanding. Once you have it roughly smoothed out, go to some 320 grit and sand it all over to prepare for primer. I use engine enamel primer since its made to withstand engine temps.
If you want this to look really good, this is where some real patience will come into play. Primer, sand, primer, sand, going to gradually smoother grits and making the surface as even as you can get it. From the 320 grit go to 400 and for the final primer coat sanding before the color coat is put on, use 600. For the finish coats I use a base coat-clear coat process just like those used on your car’s body finish.
So there you have the process. You end up with a pretty nice looking intake as you see in the first image at the top of the page and no one knows what it’s made of until you tell them or they’ve seen this tutorial.
An added benefit – with the smooth flow of this intake, the throttle body screen can be removed without issues that sometimes arise with other style intakes. This is equivalent to installing a slightly higher flow throttle body. In fact, when RAT had their high flow TB the screen removal was were virtually all of the increase in flow came from. So it’s like having a RAT high flow TB for free. (RAT isn’t really still in business and this may be one reason why.)
Need the basics of the install? It’s pretty straightforward.
- Remove the stock intake box and duct. On a ’97-98 you will need to use a ’99+ rad overflow kit to relocate the overflow tank.
- Hook the PCM down however you want, mine simply sits on the adhesive foam blocks that were holding it inside my ’98 airbox.
- Install the rubber and stainless steel coupler on the small end of the new ABS duct you just made and the filter on the large diameter end and then slide it onto the throttle body, position the way you want it and tighten it into place.
CAUTION. Many that have done the basic ABS intake don’t make sure the PCM wires aren’t rubbing on the screen of the filter. When this wears through the wire insulation, and it will, then funny things start happening depending on which wire’s insulation is compromised so you may want to sleeve your harness. I’d imagine that if the right wires were shorted from this that the results could be very undesirable.
ANOTHER CAUTION. Check your new intake regularly after installing to insure it’s tight and the filter has not fallen off as the ABS shrinks a tiny bit. Give it a check over each time you check the oil or whatever you’re doing under there.
