Okay, as promised long ago, I finally got around to taking some pics of my Jag triple SU setup. This should give some a better idea of the arrangement of three SU carbs . Remember, these are the 2"/50mm HD8 SU, so they are different than the Hitachi ones. (Side note: I'm looking to unload these soon, if anyone has an XKE or XJ that needs carbs PM me.)
For some reason this topic really gets people's hackles up, and I'm not sure why. I think the potential is great. Use the often discarded factory Z SU's (far less $ than anything else, sometimes free), jet them down or use the roadster or 510 smaller bore carbs, and get similar performance with potentially better drivability and mileage. If the factory round dome SU's are intended for good stock performance on a L24, why wouldn't three be in the ballpark for a seriously modifed L28 or stroker pushing over 200 rwhp?
The twin SU manifolds for the 510 could be used as a starting point to weld something up (1 carb to 2 cyl vice 1 carb to 3cyl). If you look at the second pic above you can see Jaguar's common plenum above the individual runners, eliminating any firing order/intake pulse issues. I think you would want to duplicate that, or at least run large diameter tubing linking the runners together, like a fat fuel rail. That is something I feel the guy on Classiczcars did not do adequately, it only looks like 1/2" tubing.
I am very surprised no aftermarket manufacturer tooled up in the seventies to make such a manifold. How many SU's got thrown away? I think it may have something to do with the percieved "sexiness" of Webers and Mikunis, and America's love affair with the 4 barrel. I think the three SU's in a row look pretty damn cool polished up.
An interesting thing I noticed about the inlet plenum/airbox can be seen in the pic below. The carb inlets are dropped off the main header, and have little flow directing vanes before the throats. I assume this is to minimize turbulence at the carb entry, which is a common issue on a ram-air box with carbs. I like it.
(here you can see the linkage arrangement)
The Jag guys I've spoken to feel very strongly about the performance, drivability, and ease/lack of continual tuning with the triple SU's vice Webers. A GT winning race team in the early 80's did much dyno testing and concluded they out performed Webers on the Jaguar l6. I'm sure that may not be true in every engine's case, but they followed their testing, used SU's in competition even though they had the option to use other carbs, and ending up winning a championship.
I'm in no hurry to tear off my Mikuni's, but I like this idea alot. I will fart around with it in my spare time, and hopefully end up with something I can test back to back against the carbs on my car. Call it a mental engineering exercise, or a waste of time. My neighbor is an alum welding genius, I'd hate to let that go to waste...