Why I Use OEM Filters (At least for now)

Intakes are a popular early modification for those of us that want more power from our cars. Intakes aren't too expensive, they're usually easy to install, and they give you instant gratification in more power and more noise. But are they worth it? How do they make more power? Why are they louder? Keep reading for an overview of intake systems and how they affect your Aston Martin!

Intakes and Aston Martins

Let's start off with an overview of the intake system on an Aston Martin. I made a nifty little video of it on my V8 Vantage (the V12 cars aren't much different). Here's it is if you haven't seen it:

As you can see, we've got a few main components:

  • Inlet
  • Air box
  • Filter
  • MAF sensor
  • Piping
  • Throttle body
  • Intake manifold

Every car is built a little differently, but they'll all have these things in common (I'm not going to get into non-MAF systems, carburetors, etc). They're arranged in a path so air passes through each one in a chain-link series of events. I'll be making some generalizations as I go through this - this post is going to be long enough without getting into things like turbulence, laminar flow, and velocity.
 

The Inlet

The inlet to the intake system is the first piece of the puzzle. This is where air first enters the system from some source. The size of an inlet is a balance of air supply required, air source, and intake filter protection. Each of these has a cost or risk associated with it.

Generally speaking, the bigger the inlet, the more air that can get into the intake system. On our cars, it's at the front of the car. The V8 Vantage has a central inlet behind the main grille. The V12 cars have them on the sides of the grille. These locations ensure you're getting a LOT of cool air while driving. If the inlets are too big, they'll basically act like a parachute. The inlets also take up space in front of the radiator - so the bigger the inlets, the less airflow there is for the radiator, and the harder it is for the cooling system to keep the engine at optimum air temperatures.

We also need to consider where the air is coming from. Cold air is more dense than hot air. Dense air has more oxygen molecules, which means more power is created during the combustion cycle (thus the interest in "cold air intakes"... more on that later). Our cars take air from the front of the car, so it's about as cold as it can get. If the inlet was in the engine bay, it'd be taking in hotter, less dense air, which means less power potential.

And then we have protection. The inlet needs to be located in a place that ensure airflow is uninterrupted. If the inlet was at the bottom of the car, driving through water would seal it and airflow would cease. Worse, your engine may suck up the water and destroy it (this is called hydrolocking). Some people take protection to the extreme by creating snorkel inlets. These offer maximum protection of the inlet's air source. You can see the snorkel running up the A-pillar to place the intake inlet at the roofline:

The Air Boxes

Next we've got the air box. This has two main functions: 1) protect the intake filter, 2) reduce noise. Protection is especially important on our cars because of where the filters are located - low down in the front of the car. Not just low down, but very low down. This puts them at a great risk of water damage (which can be anything from the fouling of the filter media to hydrolocking the engine). If you're not worried about the risk, you can modify your air box or eliminate it altogether. My car had "Swiss cheese" air boxes on it when I first bought it.

The Swiss cheese approach gives you the benefits of eliminating the air boxes without completely doing so. However, you can see that there's still a lot of exposure water damage. In the next section, Air Filters, I'll cover why this matters. The other downside, of course, is that it's non-reversible.

Since the intakes are positioned so far away from the cabin, and from the intake manifold itself, we don't need to worry about intake noise. On a turbocharged car, eliminating the air box makes a huge difference. You'll immediately notice a whooshing sound while revving the engine as you can actually hear the air being pulled into the engine. But for us, between the air boxes being so far away and engines being naturally aspirated, all we care about here is protecting the filter.

On those cars with the N400 intakes (including the Power Pack retrofit, the DBS, V12 Vantage, V8 Vantage S, V8 Vantage GT, etc), there's an extra inlet in each air box. This increases the overall amount of air that can get to the filter, increasing power potential.

The Air Filters

The job of an air filter is a two-part balancing act. On one side is air flow and on the other is filtration. If you seal off the intake system, no contaminants whatsoever will get into your engine's intake system. Unfortunately, there won't be any either, either. If you leave the system completely open, you'll get a ton of air, but also a ton of contaminants. Filters offer a happy medium, but at varying degrees in that balancing act.

The vast majority of cars (if not all cars) use paper filters from the factory. Paper filters offer the best possible filtration while also allowing air to pass through. The vast majority of performance aftermarket air filters (if not all performance aftermarket air filters) use cloth or foam media. These allow air to pass through much more easily, giving your engine a greater supply of air but at the cost of reduced contaminant filtering.

Here's a picture showing the filter media density of an aftermarket oiled cloth filter (foreground) and paper OEM filter (background). You can see how loose the cloth is woven and how easily contaminants can pass through compared to the paper filter. The filter I disassembled has two layers of the cloth pressed together, but you can still see how loose the weave is despite that.

Some filters make up for the lack of filtration by using oil. This greatly improves the ability of cloth filters to prevent contaminants from getting through the filter, but it isn't without risks. The primary one being the potential fouling of the MAF sensors. I am not personally a fan of oiled filters. I've replaced bad MAF sensors before and, to me, oil filters just aren't worthwhile.

If you plan to run open or Swiss cheese air boxes, you need to keep water ingestion in mind. I did another intake video showing how much protection each filter type provides from water damage. The filter media in the picture above was taken from the filters you see in this video.

Paper filters make up for their restrictive filtration media by adding a lot more surface area. Youeasily can see in the dunk test video that the OEM paper filter has a lot more folds than the aftermarket cloth filter. The additional folds add more surface area, thus increasing the amount of air that can pass through. The difference? In this case, the aftermarket cloth filter dissassembled was 7 feet long. The OEM paper filter? 18.5 feet! The filter was so long I had to cut it down for measurement and comparison against the cloth filter:

The MAF Sensors

Mass air flow (MAF) sensors tell the engine management computer how much air is getting into the engine. They're very fragile sensors so protecting them from damage is essential. If they do get damaged, you'll get erroneous air metering readings and your engine won't run right. If the MAF sensors do get bad enough, you'll get a check engine light (CEL) and a fault code telling you which MAF sensor is reading incorrectly. The MAF sensors are located almost immediately after the air filters, so air filter choice is very important for protecting them.

The Piping

Piping is just that - it's the intake pipe(s) that air flows through to get to the intake manifold. The pipes in our car are corrugated plastic. This isn't uncommon in cars, as the corrugation (the accordion-like design) allows the pipes to flex and move to compensate for engine and chassis movement while driving. Without some way to flex, the pipes could break or become disconnected and unfiltered, unmetered air could get into the intake system.

The Throttle Body

The throttle body on the V8 Vantage is actually quite large. The V12 cars have a pair of throttle bodies - one for each engine bank, effectively creating two inline-6 engines with a shared crankshaft. Our throttle bodies have a tendency to get dirty over time, causing them to stick rather than operate smoothly. It's a good idea to clean them while doing your annual service to ensure they continue working correctly. (I'll update this blog post with a link to a yet-to-be-made DIY guide for cleaning the throttle body.)

The Intake Manifold

Lastly we have the intake manifold. This is the big metal thing that sits on top of your engine. Its job is to distribute air to each engine cylinder. Intake manifold design has a direct impact on your engine's power delivery. It's one of the reasons why the DBS and DB9 had different power outputs from the same engine. The DBS intake manifold had shorter runners (the 'legs' leading down into each cylinder), resulting in power output being focused higher in the rev range. The DB9 had longer runners, resulting in power output being focused lower in the rev range. This was done to give each car a different power characteristic (the DBS being a more sporting car while the DB9 is more of a grand touring car).

Choosing an Air Filter

As the title of this blog post states, despite all the work I'm doing to get more and more performance out of my V8 Vantage, I'm still using the OEM paper filters and including them in my 2-year service packages. The paper is restrictive, but there's a ton of surface area to compensate for that. You can get more power potential by reducing restriction but for me, personally, the risk of an oiled cloth filter just isn't worth it.

I'm still researching aftermarket filters to find one that meets my expectations - and from a company that's willing to work with a small company like mine. I can sell K&N filters. A lot of people love them and they do produce power for the very reasons I've explained above. But they aren't listed in my online store because I can't put my stamp of approval on them. I sell the things I do because I use them myself and can stand behind them (well, I haven't used a set of KW coilovers yet because I can't afford them lol... but they make excellent products and are a great company, so I'm comfortable listing them). When I find an aftermarket air filter I'd use myself, I'll slap a set in my car and list them on my website. In the meantime, OEM it is for me.

Redpants Updates

The washers and O-ring that should be replaced during gear oil changes has been added to the online store.

The Lamy pen found in cars with the updated interior has been added as well.

And I've updated the DIY Guide for removing the armrest and center console with pics showing the extra screws that need to be removed from the newer armrest found in the updated interiors. (Thanks, Mike!)