Just took my car in for an oil change before the weather starts getting nasty and I don't get it out that much. When I got home I decided to open the engine compartment and make sure everything was in order and no damage had been done. I couldn't believe how hot the engine cover and intake tubes had gotten (mind you this is the replacement MB SLK 320 Cover). I had only driven home about 5 miles over about 15-20 minutes since the oil change. I left the car in the garage and forgot about it. About 2 hours later I went down to the garage to check on things and the cover was still pretty hot so I removed it for closer examination in the house next to the Crossfire cover. The 2 covers are virtually (other than cosmetics) identical. I thought perhaps the MB cover was using a more restrictive filter which might cause the temps to climb but EVERYTHING is identical to the XF cover. I reinstalled the MB cover and figured I'd ask the experts. Mind you I have nothing to compare this to. I've never checked the engine bay immediately after driving for anything let alone to see how hot the cover was getting so this may be entirely normal. Anyone know for sure?
P.S. Just had another thought, perhaps the mechanic disconnected the fan somehow and the engine was beginning to overheat. At what point/temp does the fan come on? Just started the engine and the fan never came on while running it a couple minutes at idle. Normal? Thanks.

 

The stock cover/air filter assembly does get VERY hot after a run due to heat soak. On the face of it this would appear to be very bad for performance, which it is to a certain extent, but when moving at speed the intake air temperature drops considerably. I've logged it via the OBD and the IAT is not much above ambient when cruising. The stock setup really is a cold air intake and a lot better than people think; certainly better than the systems that hang a couple of filters in the engine bay. As another exercise I have tapped a hole either side of the one of the filters to measure the pressure drop (if any) across it.

For information here's a pic of the temp I measured on the underside of the airbox cover after a short run - 78.2 Celsius (173 F).

 

Woody, with the increased airflow of the K & N filters would the temperature drop as well as benefiting from the increased volume of air? Could you also comment on the fan part of the first question I asked? Thanks a million, Marc.

 

Hey woody, what where the numbers on your pressure drop test at full throttle?

I figure the air box is good enough for the cars performance output, but I did remove the holsters where the two plastic air intake tubes slide into the grill, they where the most restricted part of the entire intake system! Don't believe me check it out, you'll see.

I'll post pictures later, I'm sure I'll get dumped on by some of you guys for removing parts from my car, but oh well, hahaha.

 

OK here are the pictures of the air intake holster things. I think all they really do is support your intake tubes, but they are smaller than the black intake tubes, so I figure to hell with them, who wants that restriction!
There is also a little flapper door underneath, which has me confused as to what it really does. The only thing I can think of is that it let's high-speed air enter the engine compartment. Probably for cooling and warm-up purposes, but now there is a larger entryway for more air flow to come in through the grill so I'm guessing it's better cooling.

As you can see the horizontal distance is only about 32cm. Yet I might be creating some airflow drag at the intake entrace due to the fact that the intake tubes don't have a clean radius to allow for proper air flow down the pipe, near the leading edge of the intake tube. Might have to spin some alluminum insert with a correct radius for the airflow to enter smoothly.

 

Hey dynamicS, do these inlet pieces just remove by removing a screw (or couple of screws)?
I'm all for taking stuff out of the car to reduce weight - but still keep it riding/looking like stock etc.

 

They're easy to remove, since they use plastic press in fasteners. Though it probable only weighs 12 oz. not much weight savings.

 

Most likely it is there to allow any ingested water to drain out.

 

I can't imagine this to be true, because it's not connected to any drainage of any sort. Take the front grill off your car and have a look, it seem to be more for fast moving air to enter the engine area for cooler airflow through the engine compartment.

 

I've not had chance to get any figures yet since I have not connected the pressure sensor up to my logger. Hopefully get some figures soon. Yeah, I think the stock setup is more than adequate for stock power. I know some people have reported feeling a difference when removing those restrictive looking intake pieces you mention though. They probably are not as restrictive as they look if you compare their total area compared with the MAF housing/throttle body area. I think this area is worth a look restriction wise as there are internal direction vanes to force the air through 90 degrees.

Just some additional info...on my limited dyno runs to 5,000 rpm there was absolutely no difference in whp running with or without the engine cover, even though my filters were the originals and pretty dirty.

 

Simon, I had the same thought. I have looked at it as closely as I can without taking it apart and the internal vanes and flaps, etc. are indeed directional and probably force more air up the intake tubes than they could "suck" with the vanes removed (especially at lower speeds). I would like to think that the engineering is much better thought out than some give credit. As your tests have pointed out, the temps are very close to ambient when running. My simple mind cannot believe removing those items will increase airflow nor reduce temps. Looking forward to more stats from your testing.

 

I've been looking at the two abs plastic intake tubes and noticed the transition from oval to circular shape is very abrupt and definitely restricted and turbulent.
To fix that I would like to find a nice velocity stack to slide in place of the oval section to take up the oval length that I will be removing from airflow path. Does anyone know of an aftermarket company that makes spun aluminum or plastic velocity stacks? Something I could just slip into the intake piping would be great!

 

Yes, I am sure the engineers at MB have done a much better job than they get credit for. The thing to remember is that they have a lot more things to take into account than the likes of us - production costs, emissions legislation, noise regulations, fuel economy, drivability and a whole host of other stuff. Here's a pic of the vanes in the MAF housing.

 

that is the next part I was thinking about replacing also...

 

Hey Woody.... I'm waaaaaiiiting, good thing I didn't hold my breath, 3 years is a long time . Did you ever get those numbers or has anyone else done any testing as to whether or not removing these tubes or pieces below them is th ebest route ot go???

I know its a longshot, but who knows....