I did have pancakes, but they were home-made from standard paper elements with 20 gauge aluminium sheet glued onto them:
photo (9) by
michaeljallen19, on Flickr
I only did this as I had fitted HIF6's after my engine rebuild and there was no way to adapt the original air filter box to fit. As you will have seen, the original HD/HS8 carb setup has a cast alloy plate on the rear of the frame which provide a radiused edge on the intake to smooth air entry. These plates also interface with the large circular locating holes on the air box. The HIF's don't have this (as you can see below), and the alloy plates can't be adapted to fit the other frame (mixture of bolt spacing and carb mouth spacing). So if you want to fit pancakes, you'll have to remove these alloy plates and bolt them straight up to the back of the frame in the conventional manner.
DSC00635 by
michaeljallen19, on Flickr
My new setup (which is an intermediary solution while I work out the dimensions and location for a bespoke plenum chamber with appropriate cold air feed) is quite simply a set of 2" ram pipes bolted onto the rear of the carbs in the normal manner with a set of Piper-cross air filter socks over them. As you can see, the HIF is a substantially more compact carburettor, so there is a good deal more space between the carb and inner wing - around 8" to the 5" with HS8's. As such, the ram pipe only occupies around a third of the available gap, which is ideal.
image by
michaeljallen19, on Flickr
image by
michaeljallen19, on Flickr
I'm not particularly a ram-pipe evagelist. I understand the benefits, but don't believe they contribute to much more than a percentage point or two in overall performance. Mine were fitted predominantly to give something to strap the filter socks to. I don't feel that the types I have fitted offer any more substantial gain than the radiused intake plates fitted as standard to the HS8's. Therefore, if you could retain them, perhaps by drilling additional holes in a pancake filter and fitting them on the inside (taking care to ensure everything was tightly bolted up with no gaps between the mating faces to induce air turbulence) I think you'd be onto a winner.
I'm also not wholly convinced of the benefits of pancake type air filters unless they have a substantially larger surface area, and even then the benefit will only be breathing at the very top end. I.e, ability to maintain 90mph+ comfortably. Personally, I feel there is a lot to lose getting rid of the original box, not least the fact that the air intake is pointed forwards to minimize intake roar (which is very audible in the passenger seat on mine). I don't think the box itself is necessarily constrictive, but rather the surface area of the filter elements. Provided you could get something thicker than these, it may be worth the change.
My first choice would be these:
http://www.holden.co.uk/displayproduct. ... de=015.164
My primary motivation was ease of maintenance and length of life. I re-oil them once a year and am away again.
But also as a stop gap until I fabricate a more permanent arrangement: a large empty 'plenum' (drum) mounted horizontally and bolted up to the rear of the carbs with ram pipes inside, a large (5"?) bore pipe leaving the front of the drum to an injection SD1 V8 style air filter box containing a double-cone cotton element conical filter, mounted next to the rad top hose where there is a small recess in the 2000 inner wing, with a large trumpeted intake pipe taking air from just behind the NS inner headlight, where the air is coolest and largely still. That's when the rolling road gets fired up!
Michael
