Airbox Holes

I have owned my car for about a year (99 C2 Cab), changed oil and recharged the BMC filter today. When I took the filter out of the airbox, I noticed previous owner had cut 3 holes in the bottom of the box. I assume to improve air flow? Anyways, you would think sucking in hot air from engine compartment would not be great for performance, however car runs great. As an aside, I have used K&N, BMC for many years, I am always amazed at how better the car runs when they are thoroughly washed and re-oiled. I thnk they tend to get clogged fairly easily.

I think the MK II 996 have small holes at the bottom of the airbox already but not large holes.

If the holes are in the bottom, the reason is to let water out...

Here's a shot of my stock air filter box, ignore the text, it was used for another post previously.

I have seen the holes in the bottom of a stock airbox which are clearly for water however what are the small drilled holes. They are much higher than the low part of the airbox so I do not think the holes are for water. I have a 1999 there are about 20 holes on the opposite side from the air inlet. The pictured airbox in the above post has way more holes than mine. Those holes are annoying because the my airfilter is usually clean except near those holes. (Sorry for hijacking the thread )

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They do. Maybe Loren or Tim knows what the true purpose for them is. I assume they are for drainage and to pull in extra air if needed.

In 1999 996's (also 993's) one factory option was called the MotorSound Package. This was designed to give the driver an aural experience when the throttle was put down. Most intake boxes are designed to minimize intake (airsucking) noise. However, the multi-hole bottoms were designed to "enhance" that noise for the drivers listening pleasure. Possibly, a previous owner created the openings to achieve the same effect because his stock intake did not have the MotorSound Package option. And it may also have been done as a way to increase airflow. Tornik550, You stated these holes were annoying to you because the filter was dirtier in those areas. Congratulations! Your filter is doing its job!

Be careful using K&N type air filters. They allow more particles into motor and can decrease longevity.

The difference in dirt let through is academic at best. I have never read about a motor that failed prematurely due to the extra dirt that a K&N type filter lets through.

THese were def cut, not molded in- see pic.

Chart505, if you need an unmolested box, I have one for sale for $100....sorry to pimp my parts.

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Jeez, that looks nasty! Done without any love whatsoever.

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Is that the Motorsound Package??

done for sound only, as long as its covered up and the airfilter is still filtering all the air to the intakes, leave it IMO - its ugly but out of sight and does not effect the function or performance of the filter and most likely offers quite a bit more sound on WOT

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You mean an alternative "orange cap" mod!?

Car runs great, and come to think of it the intake sound is a little loud but I also have the sport exhaust, so it's loud anyways. Guess I will just leave it as is, box seals up fine with the filter, etc.

And, just for the record, the pictured modified intake box is NOT the factory MotorSound Package filter box. The MS box has a series of about 40 1/4" (sorry for using a non-metric number), nicely molded, nicely patterned holes on the bottom of the box, and on the lower side. And I agree that as long as the holes in your box come BEFORE the filtered air enters the intake, then they are of absolutely no consequence (as to harming the engine). The factory MotorSound Package intake box was harmonically tuned by the placement of the extra holes to give a very pleasant tonal quality when the engine is full throttle winding out. Since MAF-type fuel injection intakes do not play the song of 6 finely-tuned Webers, the MS package was designed to return some of that string-backed leather gloves driving experience. The holes work in exactly the same way a glass Coke bottle (remember those?) does when you blow over it. The squares cut in your box would not have that same effect but would allow more intake noise and more airflow (although, if one only needed to cut some bigger holes in the airbox to create more horsepower, don't you really think Porsche would have done that already and long ago? And do you SEE the size of that airfilter? There is obviously plenty of air flow already in the stock configuration, or the filter would be smaller). The MS Package was available on 993's and the first year of 996's. It was dropped as an option in the engine change-over when throttles went from cable action to the throttle-by-wire computer stuff. The MotorSound Package also included the factory Sport Exhaust. There are no switches or computer-augmented flappers in that exhaust system. However, the PSE could be ordered by itself.

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http://www.bobistheoilguy.com/airfilter/airtest1.htm I work w/some of the best Porsche technicians in the country and they laugh when they see K&N filters. Don't you think the engineers at Porsche would use a different type filter if it increased performance and didn't cause more wear and tear on the motor?

Looking at my airbox and where the filter gets dirtiest, I have a theory that I'd like to verify with you guys. The air entering the airbox through the holes at the bottom (see picture) is significantly dirtier than the air entering through the snorkel. The fact that it is sucked in from within the engine compartent makes me think the air is also warmer (= not good). I assume that the snorkel is more than capable of supplying all the air that the engine needs, even at very high loads. I have seen a number of people drill more holes in the bottom of the airbox or even cut out entire pieces. This seems counter intuitive. I would rather close up all the holes at the bottom and just suck in clean cold air. Your thoughts? JP

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That works great in a hot climate. Once the air being pulled in gets too cold, it drops efficiency off substantially. Also, without anything in the bottom it would be easy to get moisture/water trapped inside.

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What about the "dirty side" of my theory? JP

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It's a good thing there's a filter for that sort of thing

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I closed up the holes on the right hand side bottom of the box and I filled it with water. There is one drain hole at the very bottom in the middle and it emptied very quickly. Ran it with a newly cleaned / oiled filter and there is no noticable drop in power across the rev-range. I think I'll stick with just clean air through the snorkel. JP

Tupperware might have a better option if you want to go the cold air intake route and out do the creativity of the last owner. It is amazing what a rivot gun can give for options. Yah hot air is going to be preceived as less oxygen by the O2 sensor and run things leaner than cold air. Cold air means more fuel and air so more power.