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This airbox is the pinnacle of BMW Motorsport S14 carbon fiber plenum development.
It is sized for the 49.5 mm (nominally 50 mm) slide throttles that were used in the DTM series circa 1991-1992.
The airbox also incorporates a second quartet of injectors near the inlet of the trumpets
(on this particular unit the added injectors are on the bottom of the trumpets).
These additional injectors would be "phased-in" at higher rpm to both increase fuel delivery
and improve atomization into the high velocity air stream.
As with many of the genuine BMW Motorsport carbon fiber airboxes, this one was built by the German firm "Die Wethje GmbH" and it has their characteristic sticker on the backside. A photo of this sticker is shown below. The airbox was manufactured to a very high standard in May of 1992, just at the beginning of the 1992 DTM season. An inspection of the airbox from outside and inside reveals that it was quite possibly molded as one-piece, not bonded together afterwards. It is suspected by some folks who have seen these Wethje airboxes that they used inflatable bladders of some type to push the inside of the carbon cloth against the inside of the mold during curing. |
The second quartet of fuel injectors was fed by a separate fuel rail which was bolted to the
airbox (on the bottom in this case). There are molded in "pads" to hold the fuel rail as
can be seen in the photos below. The bolting of this rail to the airbox is what holds the
injectors in place. The intended injectors are of the same shape as a regular S14 injector
and are sealed using the same O-rings.
Additional photos of this 1992 DTM airbox are shown below. The inside of the box is revealed, and there is also a comparison of this DTM airbox to a contemporary Germany "small trumpet" Gr A replica airbox. In the last photo if one looks carefully at the orientation of the intake trumpets then it is apparent why this DTM airbox will contact the bottom of the hood supports when installed on a regular S14 engine. This DTM airbox was intended to be used on a more inclined DTM engine (which actually makes the problem worse) but also with the 50 mm slide throttles, which mount the airbox on the engine in a more horizontal orientation (it takes some careful observation of photographs to detect this). Observe how short the trumpets are on the DTM airbox, indicating that it was intended to be used at very high rpm's. |
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