I think I’ve had a bit of a result with the K&N pancake filter search.
I was thinking that I’d seen something that would work somewhere but couldn’t think where. Then I walked past my Cooper S and remembered!
My Mini’s heavily modded 1340 Swiftune motor runs with a single HIF44 instead of the factory twin 1¼" carbs. I went onto Mini Spares website and there it was: K&N filter 56-9132 - to fit H6, HS6 etc. 1.75" SU carb, dropped version to fit under the Mini bonnet. I ordered a pair, and have just fitted them (almost) straight out of the box in 20 minutes. The extra time was because I just needed to drill two new holes in each baseplate for the air holes, as I want to use the baseplate inverted. Once done, the baseplate bolts straight up the carb with no other work. The nuts and bolts are easy to access with no bulky filter to hold. The now-redundant air holes are covered by the body of the carb and sealed by the K&N cork gasket which was in the box.
I’ve fitted the front one upside-down, to clear the bonnet flange, and the rear one the right way up to allow my arm to get under the carb more easily for other jobs. This is not strictly necessary, and I would very much welcome opinions from those who know more about airflow etc. if it would be more desirable to have them both orientated the same way.
The front cover nut on the front filter is now the one that’s a fiddle to get to, but it’s not as bad as the mounting screw on the original. As the plate is flat it’s very easy to fit to the carb now.
Photos of 56-9132 filters installed:
New holes drilled:
View from rear carb looking forward:
‘Stepped’ view from above:
‘Stepped’ view looking forward:
Much easier access, and massively better filtration.
An engineer’s opinion on having the filters in this stepped position would by very welcome!