I've seen the transition of Air Box Tops (where the square 2L air filter sits inside) from the start of the 2.0 4 Cyl. model's introduction in the 1973 MY - starting in 8/72 build dates.
They progressed from a Diamond pattern of stamped ribbing in the top,
... to just straight top ribs later in the 73 MY (see topic: "The Few, the rare......" Sahara Beige in O&H),
... to plain flat & smooth in the 75 or late 74 MY IIRC (correct this if I'm wrong).
So maybe others could post pix here of the variations & examples on their 914-2.0's for others to see the differences, as well as for some looking to find to "correct" Air Box to restore their D-jet 2L!
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Now just to confuse things a bit - apparently the VW Werke & Karmann plant(s) decided to use 2 different versions of the Diamond Top Air Boxes - side by side on the production line - at least in the first few months!
So maybe others with early-73 MY 2Ls can also weigh in here with pix of their Air Box Top Quirks as well!!!!
Okay, I'll start with these two early 73's - so aside from this Signal Orange 2L having what would appear to be an erroneous build date sticker, or else it was delayed until after 8/31/72 in its completion - this 914 was built a week & a day before mine, has a VIN 852 before mine & a GA engine 88 before mine .........
... and yet for a week apart & probably on the line at the same time - look at the difference in the stamped top ribbing of the two air cleaner boxes - both of which are the same part number !!??
Air Box for My early-`73 MY "914S" / 914-2.0 - VIN 4732901954, 2.0 Engine # GA000424, Chassis No. 3649545 ( = 8/31/72):
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> Note than mine above has the 4 additional straight cross-ribs - in addition to the Diamond Top Pattern in the one below .....
Air Box for Signal Orange early-`73 MY "914S" / 914-2.0 - VIN 4732901102, 2.0 Engine # GA000336, Chassis No. 3539559 ( = 8/23/72):
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... Hmmmmm ...... so many differences & quirks in our 914s...........so little time!