Shinigami

More specifically, the difference in sound. I want to understand what is it that causes sound to be larger when using, for example, a K&N cone filter rather then the standard airbox filter.

Just like the S2000, my SLK 55 AMG also has an airbox with a filter inside (although it is situated on top, on each side of the engine, with tubes from the front feeding it with air).

Now, I saw that K&N makes a filter specifically for the N/A 55's, that gets placed inside the standard airboxes. But what I also see is that many people just get rid of the airboxes completely and replace the tip of the tube with a K&N style cone filter.

So my questions go like this:

1) Is there is a difference in sound between the two? Say I replaced the standard MB filters with K&N's inside the airboxes, I suppose I would increase the sound produced by the engine. But would this sound be louder if I removed the filters entirely from the airboxes, and instead added cone K&N filters at the tips of the tubes instead?
2) And what exactly is it that causes this difference in sound? Is it the form and shape of the filter, or is it just the amount of filtration by the filter itself that does this change?

I've been wracking my head trying to figure this out and thought I'd ask you guys since many of you have gone with those cone filters. I was thinking I might do something similar to this:


Thanks

VTEC_Junkie

most stock airbox serve as intake "mufflers." when replacing a factory paper filter with a drop-in K&N one, you will hear virtually no difference in sound. when you eliminate the airbox altogether and replace it with a cone filter, you basically remove the insulation which is the main reason for the increase in noise.

in your picture, the filter setup is actually a bad idea, cuz once you start driving the car, the engine bay becomes hot and you end up sucking in hot air, which vitually eliminates the possitive effect from the extra air going into your motor. a setup like that is really for no other reason than for sound.

Shinigami

Thanks for clearing this up for me. I was thinking that the airbox indeed acts as a muffler, but I found no proof of it during my google searches.

The setup in this picture has been discussed extensively on the SLK forums, and indeed most people fear the engine heat causes negative performance. I'd love to have some extra sound, and whilst K&N provides filters which replace those in my airboxes, I'd like to try a similar setup WITH heat shields installed.

I spoke with a tuning shop not too far from my home, and they mentioned that performance and sound increases are very, very small when replacing the stock filters in the airbox, with K&N's. Then they mentioned that adding a similar setup to the one in the pic, would definitely increase noise, but might result in negative performance since the ECU in the SLK is not programmed to take advantage of the extra air, and basically too much air is being rammed into the engine with the usual fuel mix. Does this sound right?

And what would the noise be like if you just removed the filters altogether? (no, I don't plan to do this, I don't want dust in my engine, but was just wondering if removing the filters altogether results in the most 'noise').

xviper

Go ahead and try it in your garage or driveway for a couple of minutes. Won't hurt anything. In fact, take off everything at the throttle body. That's where most of the sound comes from. It's air being sucked through a throttle plate and when you open the throttle plate, the sound changes and you also hear all the noises that eminate from inside the engine coming out. The airbox and the connector tubes are simply sound mufflers or enhancers or modifiers, depending upon what type of set up you have.
You seem to be somewhat fixated on the sound. Don't forget performance. You can lose a lot of HP if you place an unsheltered filter inside the engine bay (hot air does not help performance in any way).

Shinigami

xviper: yeah, I wouldn't wanna lose any power...

I don't really mind having a bit more power, but a slightly more growling noise from the engine bay would be nice. Not to say the car doesn't make noise, but a little more would be pleasant I guess.

I spoke about this setup with a local 'tuner' shop, and they said it's best to just go with replacing the standard air filters in the airbox with performance ones. I know of one other owner who has done it to their 55 and it worked, so I asked him to order the pair. It might increase sound just a tad...

If I went with cone filters, I'd have to make custom tubing, custom heat shield and possibly an air redirector. This would increase price by 5 or 6 times over the standard filters. Nevermind the fact that the setup pictured in the photo would apparently be illegal in this country =\

Thanks for the replies!