Intro:

NOTE: If you are looking for a cheaper alternative to the K&N filter setup, WIX makes a paper element assembly. You can order this from any Napa/Carquest parts store, part number 44125(?). They are spec'ed for an MGB. A pair of filters cost me $15.00 and lasted for six-months before they became dirty. A K&N filter setup will cost upwards of $65.00 for the pair, however they will last much longer than six-months. The WIX filter is better than no filter at all, and if you run them for six-months while you save up for a K&N setup, no one will think badly of you:)

You've no doubt heard the commercials and claims for K&N. There are benefits to offset the higher up-front cost of these filters. One, of course, is that they last a long time (years) with proper maintenance. Second, they flow more air than paper elements. You will notice an increase in intake noise when changing from paper filters to K&Ns. That is not a scientific measurement of flow, but you know what your car sounds like when you run without filters, right? And you know air is flowing then!

Bluebirds list member Jason Gray performed some flow experiments recently with SUs. He found that an SU with a K&N filter and an airhorn flowed as much air as a bare carb. This may not sound impressive (and contrary to some of K&N's claims), but you gain the filtration capabilities of the filter as well as a certain amount of intake-pulse dampening, aiding in flow.

Applications:

There are a few different manufacturers of filters that will work with our Hitachi-SUs. Because they are the same basic carb as the British SU carb, we can use many of the filters spec'ed for British cars. If you ever run into a difficulty finding the correct application for your SU, find the part numbers for an MGB (if you're looking for filters for your 38mm Hitachi-SUs) or Volvo (if you have the Z-car SUs). You may be able to look up part numbers for the '65-'70 1600 Datsun Roadster (for 38mm SUs) or the '67-'70 2000 Datsun Roadster or '70-'73 240Z (for 46mm SUs). Just make sure you aren't ordering a replacement element for the factory aircleaner.

Part Numbers: English-made filters

The following part numbers are for the English K&N filters and are available from Advanced Performance Technology. The metal backing plates and top covers are made from stainless steel (versus chromed metal for the American versions) and the filters themselves are supposedly of better quality. In addition the English K&N filters are available in different sizes, widths, and styles, including off-set mount backing plates.

Part Numbers: American-made filters

• Racer Wholesale (1-800-886-7223) has the complete K&N assemblies for ~$28 each. Part# K56-1390 is for the 1.5" bore SU. It's 5 7/8" in diameter and 1.75" thick, the standard SU filter.
• K&N part number is 56-1390. You can order K&N products from just about any corner parts place (Kragen, Pep Boys, Autozone, etc.).