I was pleasantly surprised belatedly to discover that the things exist. I consider the SU carb to be a thing of beauty — not only aesthetically — and am forever lamenting that the ones you can actually get sort of lock you into a sidedraught format. Most can go up to about 30° from the horizontal, provision being made to that end in the attachment of the float bowl to the carb body, but no further. Imagine my delight upon ***uring myself that I wasn't seeing things, four of them, on top of a Lagonda V12 at a local cl***ic car show a few years ago: downdraught SUs! — D4s to be precise — similar to this: I have subsequently been able to find precious little information on them online. Apparently they were standard spec on a number of British cars of the '20s and '30s — that's a Singer engine in the second pic. I've found no technical information: no drawings, exploded views, needle/jet specs, etc. If anyone knows of online sources, please let me know! According to SU nomenclature, in which the model number is the number of eighths of an inch of bore over one inch, the D4 ought really to be a D3, as it has a 1⅜" bore. The D5 has, however, consistently with the system, a 1⅝" bore. Little carbs, though, for a 4½-litre Lagonda V12: and that got me to eyeing the HS8 sitting on the shelf above my drawing board. On the face of it it should be possible to convert a H-type SU into a D-type. What I don't know is what is going on around the end of the jet. In both cases the jet is a br*** tube enclosing an annular orifice around a needle attached to the vacuum piston, but while ******* the fuel level at or near the top of a vertical jet seems straightforward, how would it work when the jet is horizontal — as it certainly must be in the D4/D5? That's why I'd like to get my eyes on some technical nitty-gritty. The detail of the damper oil filler on the vacuum bell is a bit different on the D-types, but apart from that I'm not seeing a hell of a lot of external difference. Any SU boffins on the HAMB?
Try British Superior , Joe Curto https://www.britishsuperior.com/ Or @carbking here on HAMB, both of these gentlemen have been very helpful to me with my carb questions. Dan
The Jalopy Journal
