It was on the car when I got it, but it's one of these:

K&N Air Filter

Large Oval - 45mm

I'm just in the process of changing it to a Small Oval 83mm which should fit OK under the bonnet, and is rated for engines up to 175bhp. The one on at the moment is rated for 100bhp, which is sufficient for a standard crossflow.

"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10