I have a '73 1.7 liter 914 that has been running a stock air filter element for far longer than I've owned the car. I've been looking for a while to find a replacement air filter that would just drop in, but nobody seems to make them any more (I've searched on this board, and the questions go back a looong time).
However, it turns out that a NAPA Gold 2011 will work, if you make an adapter. Since I finally had a little spare time this weekend, it was time to make one. It's fairly simple: A piece of 16ga aluminum, with an inner hole to match the stock filter and an outer diameter to match the new filter. Around the outside perimeter, I added 4 small tabs, bent up to keep the new filter in place. I also put a ring of 1/16" thick weather stripping around the underside of inside perimeter, to seal the adapter against the bottom of the air filter housing. Here are a few pics:
Here are the air filters, new on the left and original on the right.
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Here's the adapter next to new filter.
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Here's the new filter and adapter installed in the air filter housing.
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With the adapter, the new filter fits in very nicely into the air filter housing. Now I'll be able to keep my car in clean, new air filters for a long time.