The stock Volvo 850 intake is pretty good, but it can be improved upon. The stock airbox uses a panel filter. The only option for upgrading to a higher flowing filter is a K&N stock replacement panel filter which is an oiled cotton filter. Oiled cotton filters are not good for MAF sensors as the oil damages the sensor. Tests have shown that the K&N passes a lot of dirt, and it also reaches capacity (i.e. gets clogged with dirt) quickly. Panel filters are OK, but a larger cone filter will provide more surface area and smoother flow. After reading the Revspeed air filter test, I wanted to make a cold air intake based on the Apex-i Super Intake filter. It's a dry cone filter (so it won't damage the MAF sensor) made of a synthetic filtering media (not paper), and has a revised dual-funnel design now called the Power Intake. It has been proven to be an extremely high flowing filter as well as an extremely efficient one.

Most aftermarket and DIY options for the Volvo put a cone filter right on the MAF housing where the stock airbox was. Honestly, this is not the best setup because you want air to smooth out before it reaches the MAF sensor. And having a cone filter stuck right on the MAF housing does not provide enough length to allow the air to smooth out before reaching the MAF. It's also not a cold air design. This type of "filter on a stick" design sounds really mean as you can hear the turbo spool up and the CBV blow off, but the hot underhood air these intake setups suck in loses a significant amount of HP. You will be able to feel the obvious loss in HP with a filter-on-a-stick intake. I logged 60F over ambient temp increases using a filter stuck right on the MAF housing with nothing else. For comparison I logged 20F over ambient temps with the stock airbox.

To provide a quasi-cold air setup, some aftermarket intakes (like EST) add a sheet metal wall that acts as a sort of heat shield. The problem is that unless it is sealed it will still suck in hot underhood air. It's an improvement to the filter-on-a-stick, but I knew I could do better. The only real solution is a completely sealed airbox using a cone filter. The only intake that fits that description is the BMC CDA, which is a nice design but also very expensive at $300. I set out to build a CAI using a sealed airbox design for about $100. Note that to make this CAI, I had to turn the stock battery sideways. Did I reach my goal? Read on to find out.

One thing I realized right away was that the Apex-i Power Intakes were extremely expensive. New they were $125 for their universal filter and that was JUST the filter. It didn't even include a mounting adapter. The Apex-i filter has a 5" opening that has no way to connect it to an intake tube without a mounting adapter. I found instructions on the net that show how to make a mounting flange for the Apex-i out of a PVC closet flange (i.e. toilet flange) and 3" PVC coupling from the hardware store, but I chose another less ghetto method. Nissan MAF adapters can be had very cheap on ebay ($4) and are made of nice CNC machined aluminum. They also happen to fit the Apex-i filters perfectly and have a 3" outlet. I hit the jackpot on ebay when I found a barely used Apex-i Power Intake, TWO Nissan MAF adapters, a 3" to 2.5" silicone reducer coupling, and 4 stainless hose clamps for $28! The filter was used for 2 months and the guy wrecked his car. Perfect for the low budget CAI project.

Once I had the filter I set out to find a sealed airbox. It had to be airtight and large enough to fit the huge Apex-i filter inside. I considered making one out of sheet metal, but it would be too much of a PITA. I wanted this to be a DIY project that anyone could do using readily available parts. A metal one gallon paint can is the perfect size, airtight, and plated so it won't rust. I was all set to get a metal paint can, when I spotted something even better. A Rubbermaid paint can for a whooping $5:

I opened it up and the Apex-i filter fit inside perfectly. I went out into the parking lot and test fitted it in the engine bay. It would work perfectly. So I brought it home to perform surgery.

First step is to mark and cut the lid for the first MAF adapter:

Cut it out with an x-acto knife, drill 4 holes for the screws, seal with a small bead of clear silicone around the MAF adapter, stick into the hole, and attach the Apex-i filter with screws and you end up with:

Nice:

Next is the bottom. Take the second MAF adapter, mark and cut with the x-acto, and drill the holes:

Seal with a small bead of clear silicone around the MAF adapter, stick in the hole, and attach the MAF adapter with screws. Here's what you end up with:

Perfect.

Here's what the completed airbox looks like put together (the handle pops right off which I ultimately did not use):

Here's a shot looking in from the bottom with the filter mounted and the container shut:

Now it's time to make the rest of our CAI.

The other big problem with the stock intake system is the intake tube itself (between the airbox and turbo). It has an "accordion" section that is terrible for airflow. Tuners in Sweden claim that replacing the stock intake tube is worth some power gains. The BMC CDA replaces the stock intake tube with a section of tubing so I figured that is the way to go.

The stock intake tube is 2.75" at the MAF sensor, and shrinks down to 2.375" at the turbo. At the bottom the PCV valve mounts right before the turbo. To remake the whole intake tube you would need to duplicate the PCV valve mount which is an odd design and not something that is not exactly easy for a DIY How2. And since the turbo opening is 2.375" anyways, it makes no sense to replace the whole intake tube with giant 3" piping when the MAF is only 2.75". I decided to use 2.5" piping and to replace only the section from the accordion to the MAF, since I felt that the very bottom section of the stock intake tube is not a flow restriction. Also any larger piping than 2.5" and it would interfere with the stock IC piping.

I would also need a few other items. For starters, the accordion section allows for some engine movement and flex, so I wanted to incorporate a silicone hump hose in the system. I also needed a 2.75" to 2.5" reducer for connection between the MAF and piping, as well as some other bits.

I started by working on the piping between the airbox and MAF. I removed the stock airbox, then took a utility knife and cut off the stock intake tube right where the accordion stops. You can do this in about 30 seconds without even removing the intake tube from the car:

As reference, here's a better picture of what you are removing (this is not mounted on the car but is for reference only to illustrate where you are making the cut:

I then attached a 2.5" hump hose and hose clamp:

Then I stuck in a 2.5" 45 degree aluminum mandrel bend for some polished bling:

Since my airbox was larger than the BMC CDA, I had to put it pointing down right next to the battery between the frame rail and the transmission lines on the radiator. The mandrel bend lined up perfectly:

I needed a 90 degree elbow that would attach to the 2.75" MAF sensor. But the Nissan MAF adapter I got from ebay was 3". I was able to find a 3" to 2.75" 90 degree silicone elbow that worked perfectly. And since the piping is 2.5", I needed a 2.75" to 2.5" reducer:

Next order of business was to add a vacuum fitting for the BCS sensor. For $8 I found a universal vacuum fitting that doesn't need to be welded (we're trying to keep this a simple DIY remember?). You just drill a hole in your pipe, stick in the included grommet, and shove in the included vacuum fitting:

Now all that was needed was to cut the mandrel bend to fit and test fit everything:

Coming along nicely. But this is a DIY cold air intake, remember? I needed a way to get cold air to the airbox. Well, the bottom of the airbox just so happens to line up perfectly with the driver's side lower grille opening. All I had to do was add a 90 degree elbow and a short section of scrap that I cut off of my 2.5" aluminum mandrel bend.

I also found a nifty 2.5" aluminum velocity stack on ebay for $1:

Perfect to suck in all that cold air from the grill opening:

Now it was a matter of assembling the lower section using the 3" to 2.5" reducer I got from the Nissan guy, the piece of 2.5" scrap pipe, velocity stack, and elbow:

Here's what it looks like from the bottom looking up (the splashguard was removed during install, then put back into place after this picture was taken):

Once the lower section is done it's time to clamp everything together, attach the MAF plug and BCS hose and that's it. Here's some pics of the completed system:

I popped my hood and showed it to Turbobrick and the first words from his mouth were "that looks expensive!". We all had a good laugh when I told him it was a $5 paint can.

Here's the final parts list:

So I was able to meet my goal of a CAI for $100.

Obviously if you had to buy everything new you would end up spending more (about $200), but $125 of that is the Apex-i filter alone. If you look around you can get many of the materials as cheap if not cheaper than I did, and you could save a lot of money by using a K&N filter cone filter instead of the Apex-i filter like I did (you can get generic intake systems on ebay comprised of a 2.5" 45 degree mandrel aluminum bend with vacuum fitting already welded on, a filter, hose clamps, and silicone coupling for as little as $20 total. That alone saves you a lot of $ while providing over half of the components of the system. The only thing left to get is the paint can and a few silicone pieces).

How well does the new intake perform? Well, I logged temps of AMBIENT, meaning that my intake air is identical to the outside air which beats the stock airbox. The car also feels stronger (especially top end). You can't hear the CBV or turbo spool up from the intake anymore for those that are used to the sound from their filter-on-a-stick intakes. But all in all I am extremely pleased with how the intake turned out.

Accessing the filter to clean or replace is a snap as the lid just pops off the paint can when needed.

P.S. - If you don't like the blue lid (I wasn't crazy about it) don't bother trying to paint it hoping it will stick. I tried Krylon Fusion plastic paint and it peeled right off. The problem is that the plastic on the lid is so flexible (just like any Rubbermaid product) that no paint will stick. I checked Rubbermaid's website to see if perhaps the paint can comes in different colors (black lid would be perfect) but they only make one model/color. You'll have to live with the gray body and blue lid. I guess you could paint the lid as long as you never remove the lid. Once you remove the lid, the paint will crack and peel off and you'll have to repaint it. But theoretically the only time you should have to remove the lid is every few years when you go to clean or replace the filter, so I guess spraying the lid with another coat of paint at that time is not that big of a deal.