Reading through an ancient 'Modern Cycle' mag, advertising things like Yamaha's new 'torque induction enduros'
( reed valve trail bikes)..
& there's a K & N ad, from way back - when - along with their trick air-filters - they offered MX handlebars,
"shatterproof" plastic front mudguards & yes,
- 2-stroke expansion chambers, for "competition" - in both "upswept & downswept styles"...
Who knew?
These days, some anorak would likely cream himself..
.. on getting a K & N branded competition pipe for a vintage MX parts display..