Air Filters

As far as air filters, I recommend that you upgrade to a K&N Filtercharger (part number: 33-2784). This filter is readily available in Europe but difficult to find in the USA. Again, JAE carries these and usually has them in stock.

As far as air filters for 4-cylinder Esprits are concerned, here's some parts to cross-reference to: 

Lotus...............A907E61827H 
Lucas...............F9164 
Beck................042-0976 
Big A...............94005 
Coopers.............AG487 
Fram................CA3166 
Wix.................46005 (discontinued) 
AC  Delco...........A1337C 
Hastings............AF44 
Purolator...........AF3223 
Geon................48-0358-9 
Mann................C-4368 
World Parts.........W27-606 
Jaguar..............XKE 70-71 & XJ-6 70-78 
Triumph.............TR-7 77-78 & Stag 70-73 

Note: The Lotus air filter has a thick rubber gasket along its perimeter. This gasket is usually sold as a separate part from the filter by most Lotus parts vendors, but is not included with the filters listed above. You can simply remove it from the old filter and re-use it.

For V8 models there are several options beyond OEM. These are made by ITG, Amsoil, or K&N.