[ROVERNET - UK] Aftermarket air filter revisited

Fletcher gofanu at usachoice.net
Thu Mar 1 05:46:57 GMT 2007

Further info on the aftermarket filters on Steve Lawrence's TC that I 
berated a week or so back. I have an MGB here with the same filters, 
only for HS4 carbs, and decided that I would calculate the effective 
sizes. I knew they were bad, but this are rrrdiculous!

Crappy "Stellings & Hellings" filters for HS4 SU. May not be real S&H, 
but the design is so bad as to make this irrelevant.
These are the chrome ones with perforated chrome sleeves on both sides 
of the foam element.
Airflow area available:
84 holes @ .190dia. = 84 x .095sq x 3.14 = 2.38 in sq per filter.
That is maximum at the inner sleeve, reduced by alignment of the similar 
outer sleeve and foam.

Airflow area of OE paper, gross:
3 3/4 D X 2 deep x .8 estimated screen coefficient = 33 in sq per filter.
Actual element is unfolded size = .550pleat width x 2sides per pleat x 
3depth x 76 pleats = 250.8 in sq.
Note that ONE pleat has nearly 50% more filtering area = 3.3 in sq. than 
the entire S&H filter!
The S&H has about 7% of the gross and 1% of the element area available 
in the OE unit.
This means that not only is it very restrictive, but also that air 
velocity in the media is so high as to make any useful filtration 
S&H also has an bad backplate, further restricting air flow, and it is 
so flimsy as to not retain the gasket, which shrinks into the intake, 
making it worse still. The car I am working on has about a 1 1/4 hole 
through the shrunken gasket, which is the correct 1 1/2 original type.

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