A fresh take on the Mr.5 air intake mod for N54 E89s

[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 hole 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…

[Pondrew]

Even though I have absolutely no interest in any of this stuff, Peter, it is good to see you back after your little sabbatical on the Bimmerpost forum (yes I'm on there too just not the Z4 bit. It's a bit 'American' for me)!

[B21]

So an interesting day on the dyno…

For those who can’t cope with a detailed dissertation here’s the distillation of over 25 dyno runs over 2 years…

The stock airbox and paper filter are good for about 400bhp…there is a very small, less than 10 BHP penalty for the airbox and filter together..I’ve not tested DCIs but haven’t seen any evidence to suggest they would do any better.

However, once you go past 400 BHP the stock filter first then the stock airbox design progressively inhibits the power.

At around 500 BHP the paper filter creates a 29 BHP penalty compared to the stock airbox with no filter in it..a foam filter has a 23 BHP penalty.

This shows that any filter is getting to the edge.

It turns out even the empty airbox with no filter is now restricting the engine..

With a Mr.5 auxiliary inlet ,with blended airflow into the inner plenum with exactly the same tune the stock airbox with paper filter generates 25 BHP more than the otherwise stock airbox with no filter ie around 526 BHP

Or put it another way for the same tune you get nearly 55 bhp more if your tune is good enough for a Mr.5 Mod

[axelleveau]

B21, those are awesome and interesting results and despite the Mr5 mod being clever: it seems time to develop a bespoke performance air box replacement

[B21]

B21, those are awesome and interesting results and despite the Mr5 mod being clever: it seems time to develop a bespoke performance air box replacement

It took me 8 weeks, 9 metres of plumbing pipe, 42 connectors of various types and 5 stabs at various foam filters to crack it..following where others have gone before...

My dyno guy says they do lots of development work for many filter /intake suppliers and most of them are worse than the stock airbox and filter..

They were shocked at just how good it was..they re-ran the dyno over 10 more times cause they were convinced it was a freak result..

I'm surprised, relieved at the effectiveness of the mod..having spent £100s on dyno time I know I could spend £100s more to probably not get much more..

Feel free to go ahead and design a new airbox that's efficient, quiet and offers good filtration..