Tii air box upgrade

Table of Contents

Tii air box upgrade #

(with thanks to Jeffrey Kok for the concept)

Many Tii owners fit the after-market K&N single air filter to their Tii’s but apparently, it’s not that efficient or an improvement including myself. Jeffrey Kok who is a wizard on these cars (from The Netherlands) told me who to modify the original air filter housing and replace the K&N filter with a better set-up using the old Tii filter housing.

Above; before the K&N air filter installed which unfortunately sucks in warm air from the engine compartment

Parts required;
• Tii air box
• Tii air filters or Porsche 356 upgrades (try searching Amazon or eBay)
• M8 threaded rod approx. 500mm long
• Two M8 wing nuts and spring washers, or M8 nylon lock nuts
• Paint and primer (your choice)
Optional parts;
• Replacement M6 x22 Hex bolts BMW Part No.07119904505
• Rubber washers BMW Part No.16114080148
• Washers A6 Zinc coated BMW Part No. 07119903791
Obviously now is the time to repaint the airbox so it looks nice in the engine bay. So after rubbing it down, degreasing it, etch priming it and coating it in several layers of matt black or colour of your choice.


This modification does away with the two original ends of the Tii air box, allowing more air to be sucked into the engine via the now larger surface area of the two end filters.
You need to drill a hole in the centre bracket at both ends of the filter housing, now Jeffrey welded his threaded rod in place, but I thought it could be ‘tapped and die’ with a lock nut installed instead, but be careful when drilling the holes to insert the rod as if this breaks you’ll need to weld it up to support the inserted M8 rod.

It worked, then drill an M8 hole in the centre of both air filters and insert onto the newly install rod. Measure the rod to allow for either two wing nuts (either end of course) and a spring washer to fit. Carefully cut the rod to size and install the air filters on either end. Refit to original air filter housing, ensuring the rubber collar that joins to the inlet plenum isn’t split anywhere, bolt into place also refitting the brackets the correct way round (you did check before removal I trust?).

I did notice a nicer inlet noise on the air being sucked into the engine, I also thought it felt more powerful (or was I kidding myself?). But in theory it should allow more colder air into the engine than the single K&N filter as the air has time to cool inside the air box and more surface area as utilising the two filters than one, also where they are positioned is better than centrally when there is more heat generated.

Above – threaded rods need to be cut down once filter in place (Porsche 356 filters can also be used)

Above; Completed plus period sticker installed – thanks to Kos