[B21]

A few words and pictures on my version of what is known as the Mr.5 airbox modification for N54 engines as in the 35i/35is.

A bit of history for those not au fait with this matter…Mr.5 was a member of a US based E90 forum who proposed an alternative option for addressing the issue of limited airflow when a N54 engine is tuned.

Many folks went down the route of two dual cone intakes, each one sitting on the end of the disconnected turbo pipe inkers after the stock airbox was removed. The counter arguments to this are the much poorer filtration of the DCIs and the induction noise they create…In addition there were arguments about heat fade caused by sucking in hot air in the engine bay.

Mr.5 suggested retaining the stock airbox and filter but adding an additional air inlet post filters to the interior plenum chamber. Subsequently he and many others came up with various interpretations of this design.

Here’s my version made out of 50mm waste pipe fittings plus a Pipercross Viper aftermarket generic inlet / filter kit.

I’ve done a blended intake on the inside of the plenum chamber, most designs I’ve seen just terminate in a hold in the side of the plenum chamber.

In the end the flexible pipe and lovely aluminium inlet were redundant as there was not enough space to add those..

This is fitted to a RHD 35is..not sure if it would work on a LHD.

Off to the dyno next week to see what impacts it has.

Previous experiments on E89 air boxes showed a small improvement in power and torque ..on a N20..4 BHP in 300…on a N54 6 BHP in 400 and 10 BHP in 500 by removing the airbox lid and / or filter parts..never tried DCIs but the dyno guys rated the impact broadly similar to an unrestricted airbox ..ie no lid ..

One of the great unknowns with all these things is not just how restricted or not certain parts of the system are but how these things interact as a function of rpm and load..an area known as fluid dynamics..for mere mortals the only way is to suck it and see..I’ll report back on the dyno results…