1.9Liter Cold Air Intake for <$30!!!(LONG) (archive)

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I got tired of waiting for a cold air intake from Dinan or whoever for the 1.9 and didn't really feel the cost would be worth it anyway. I also don't like the K&N filter-chargers (and the like) because they don't get cold air and I don't think they filter as well as the stock BMW paper filter.

So, last night I built one and installed it in my '96 1.9. I figured all the other 1.9 owners might be interested.

It increases the air intake hose into the air box to a 4" diameter hose. The stock intake looks like the smallest place for the air is the snorkel on the passenger side next to the radiator. It's not, there was a 1.75" diameter funnel into the air box. That's about a 700% increase in surface area for air to flow through easier.

Dremel with a heavy duty cutting wheel as well as the dime sized metal bladed circular saw and one of the grinding stones.

Go to the nearest 'Home Depot' or the like and in the ventilation section get an aluminum 5" to 4" duct adapter. This is a tubular piece to allow a 5" hose to plug into a 4" hose and should cost about $5.

Go to a 'Pep Boys' or whatever and in their ventilation section they should have a 4"x72" air intake type of plastic hose for about $15. Anything similar should work OK but make sure it's flexible. The stuff at 'Pep Boys' worked really well and is very smooth on the inside for better air flow. Also get a 4.25" hose clamp for a buck or two.

First thing you need to do is to make the 4" to 5" adapter shorter. To do this on the 5" side of the adapter, right at the end of the funnel, you need to cut off the rest of the 5" side with the Dremel and the heavy duty cutting wheel. (Use eye protection!) There is probably a ridge around the adapter at this point where the 5" piece connects into the funnel, just use that as the guide to cut. This isn't at all a critical cut so don't sweat the details. Then use the Dremel with a grinding stone to make the edge of the cut smooth and to grind down a 'lip' on the inside of the cut if there is one to improve airflow. This will become the inlet into the air box.

It would be helpful if you have the car up on ramps or jack stands but it isn't required.

Now you need to get the bottom half of the air box out of the car. To do that release the four clips holding the top of the air box on and move the top aside. Take out the air filter and put it somewhere clean till you are done. On the fender side of the air box there are two 10 mm nuts holding the air box in place. Remove them.

Above the radiator is the big black plastic box which holds the stock intake hose. Take the cover off of this by removing the (4) 10 mm bolts. Two are right in front of the plastic box in plain sight, the other two are right behind the plastic box. Lift the cover of that off and put it out of the way. You will now see the stock hose and where it connects to the snorkel on the air box. Just pull that hose off and the bottom of the air box can be removed from the car. While you are at it disconnect the other end of the stock hose and remove it from the car as it's not needed.

Now with the bottom half of the air box out of the car remove the external snorkel from the box. There is a clip on it that will let the snorkel slide off the box. Notice how tiny the hose is at the end of the snorkel! Next the internal funnel needs to be removed. There is a clip on the top of that that lets you take that out along with the sound deadening material and it's plastic frame. Don't worry if you break some of the plastic frame pulling it out...I left mine out and it's not a problem.

Now comes the fun part, you need to cut a 4" hole where the stock hole is. Put the 4" side of the adapter over the hole, on the outside of the air box, and draw a new circle on it with the marker. Don't center the new hole over the old one. I used the front side edge of the existing hole as the front edge of the new hole. You need enough room inside the air box for the shortened 5" side to fit in.

Using the dime sized metal saw in the Dremel, cut out that 4" circle. This is the most time consuming part of the project and hot nearly liquid plastic is going to be flying around so be carefull! Be sure to also look inside the air box as in a couple of places there are plastic ribs and such that you need to cut from the inside for the hole to come out. After you get the hole cut out test fit the adapter into it. The adapter should fit through the hole but stop at the first ridge before the funnel. For the test it's easier if you just put the 4" side through the air box from the outside but this isn't how it will be when you are done. If you can't get it to fit use the grinding wheel to smooth and enlarge the hole. It should be as tight a fit as you can make it without distorting the adapter. After you have the adapter fitting in the hole remove the adapter from the air box. Scrub out the inside of the air box with a brillo pad or something similar to remove all the plastic bits that got thrown around when you cut the hole. After you get it all cleaned out dry it.

Now put the adapter into the air box for real. What was the 5" side goes inside of the box with the 4" tube pointing out the hole. Only have the tube protrude from the box up to the rib on the tube hitting the inside of the air box. Any further and you may have a clearance problem. Now from the outside of the box seal the tube to the box either with hot glue or silicone.

A slight air leak here isn't critical, as it's still before the air filter, but do the best you can. If you used silicone make sure you wait 24 hours for it to cure before you continue.

Now slide the 4" air intake hose over the tube protruding from the air box. Secure in place with the hose clamp. You could cut the length down to about 3-4 feet now or you can wait till it's installed before doing this.

Now reinstall the air box into the car. The tube and hose should just fit into the car but it will fit if you cut the hole correctly. Put the old air intake cover back over top of the radiator and put back in the (4) 10 mm bolts. Reattach the (2) 10 mm nuts holding the air box in place. Put the air filter back into the air box and secure the cover to it with the 4 clamps. Be sure you get a good seal.

Now route the hose pretty much straight down along the side of the radiator. This is easier to do from under the car but is manageable from above. You can then either leave the bottom of the hose flush with the underside of the car or you can route the hose into the opening that leads into the front bumper, right in front of the wheel. This is where I currently have my hose going. Cut the hose to the needed length. If you run the car on the track you might want to leave enough extra so that you can bend it around to the bottom of the car facing forward (like a brake cooling duct) and have it act like a scoop for a ram air effect. On the street this wouldn't have enough ground clearance and could cause problems in puddles.

Tonight I am going to use my G-Analyst performance computer to see if the car is any quicker to 60 or in the quarter. It feels a bit stronger and revs harder for sure. I don't happen to have a dyno so I can't test it that way though.

I am also working on a scoop to fit behind the fog-light and such to get more of a ram air effect. It's fairly large so to put it in place I will need to take a bit of the car apart and I am not sure I am going to bother as I am not sure if enough air flows through there to warrant it. I may also put an air inlet into the black piece of plastic next to the fog-light. That is covering up a hole though the bumper that air could flow through. I'll probably cut out the middle of the plastic piece and cover it with a black mesh so it looks pretty much stock but flows much better.

I am also going to see if I can find a low profile type of scoop to go on the bottom of the car that the hose could connect to. I am kind of hesitant about that because of an increased chance of hydro-lock which would ruin anyone's day.

While you are at it it's probably a good idea to change your air-filter. Mine has 18,000 miles on it so a fresh one won't hurt. I am also going to disconnect the battery tonight so the computer will need to relearn the flow characteristics of the engine in the pursuit of more power.

If anyone is afraid to tear into their air box contact me and we will see if we can work something out if you ship me yours.

'96 Z-3 Red w/tan leather, trip computer, heated seats, Remus, HMS Strut Brace, RD Sway Bars, M Roadster shifter, broken sending unit(AGAIN), CD, McIntosh MC-427, BA Pro 6.5s and a Fogged air box.

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