You may have heard about UPD air intake spacers, or Cold air intake (CAI) spacers, or VRP air box risers. Let's answer three top questions about them.
What are they?
In various Mercedes engines the air intake is actually fairly good, especially when blessed by tuners such as brabus. However, there is often a lot of room for improvement so that Mercedes Tuners can get quite a bit of extra horses from them because they have some restrictions from the factory.
Does Mercedes really have air intake restrictions?
The restriction is so bad that K&N and after market filters really do add about 5hp to the rear wheels when dyno'd according to UPD.
What do the air intake spacers do?
Air spacers, larger air boxes, and air risers all attempt to reduce, or eliminate any restriction in the air box presented by the filter medium itself. The filters Mercedes choose to use on the M278 for example is very thick and takes up as much as 33% of the air intake.
AMS or Alpha performance makes new bigger air boxes out of carbon fiber presenting larger air flow throughout. On the other end are little "Lincoln log" air risers from VRP which are cost effective and reduce most of the restriction. In the middle are UPD air intake risers which when combined with a smaller filter completely eliminate any air intake issues.
Are they worth it?
100% worth it although I should be more specific as the prices on these things are everywhere. I went with a UPD air intake spacer. I was quite impressed with the quality but the install is a little finicky with the bolts. I combined this with a K&N air filter. UPD Claims as much as 35 hp improvement over just a K&N air filter. I believe it, this mod with the air filter makes the car feel much faster.
What do people say about them?
Find discussion of the UPD Air Intake Risers here:
From the UPD product page:
Do Aftermarket Filters and Risers affect Intake noise?
Yes, the turbos are much more clearly heard.
Also consider intake tubes if your Mercedes intake tube is ripped.