Adam is correct.
The issue with DCOE 45's verese HD-8's is that the SU's make more usable low end torque, only about 10% less upper end power, but need more tuning to ensure the linkages and needles and dashpots are in calibration. Balance is an issue with CD's and any SU's verses the DHLA's or DCOE's. The inital calibration envelope is very, very hard to perfect when you add twice as many extra fuel distributions points. They are also hypersensitive to intake air temperature, ignition curve , engine heat, cold start strangling, and vibration, especially on a hemi (OHC Ford, DOHC Jag XK, Aston Martin DB), or semi hemi sixes (like the 265 Hemi and 250 X-flow).
These frequently foul plugs because the warm up phase is lousy with Webers or DellOrto's. Never is a proper heat stove used. Each carb has twice as many progression circuits, jets and air correctors than an SU. Since the calibration is a compromise which cannot be trimmed to suit condtions, and the initail calibration must be spot on to the worst case condtions, it is often out. Chrysler Australias calibration for the E37/38/48 and 49's was based on a 6000 mile cruise around Italy in an early VG Hardtop, and it was at best a compromise over likely altitidues and operating temparatures. The carbs were just like DB5 or DB6 Webers, and rather like Ford's XE EFI using the 632 CSIA auto calibration for its LE-II EFI, the benchmarking was done on a European car before being transferred to the Aussie car.
David Vizard says there are no pre-jetted combinations, as there is always at least another 5% to 10% by blueprinting the carb, and further dyno tuning. Its nothing for a perhaps 300 hp engine to gain 40 hp (13 %) by ideal jetting and realted optimisation. With the SU's, you can get very close to idlea jetting becasue the needle does the same as a throttle vane in a Bosch K or LE II set-up. It varies like a MAP sensor or Vane meter, while inmproving vaccum. That's why HIF44, 6, 7, 8 carbs survived into the emission era, but the Webers and DellOrto's died off in 1978 to 1985. There was a huge range of very advanced upgrades by Skinner Union in 1978 to 1990, with a very simple but complex in operation part throttle lean-off device, and bulk density fuel level calibration, and the dreaded Air Valve on the throttle butterfly which lost about 15 cfm of flow an an HIF 38, but allowed the car to pass the Eurpoean Common Market emission regs. So its far easier with triple SU's, they are like three Bosch K jetronic systems in one.
The base line numbers by way of example are 282 gross with triple HD8's, and 314 gross with triple Webers in a twin cam DB6. That's the 10% gain with Webers I refer to. The same carbs in an E49 Charger was reported by Leo Leonard to give 295 hp net blueprinted or 306 hp factory gross or some such.
For maximum power figures, the Weber and especially the Dellorto are great in a race, but come at expense of low end tractorbility, where cars spend most of there time on the road. Here the SU's excell.
Actually, the 4 Liter DB5GT, DB6/DBS and 265 Hemi are undercarbed. The recommended venturi size from Webers rpm/capcity chart was about 42 mm at 5500 rpm, not the 38 to 40mm at 4800 to 5300 rpm which was all Weber 45 DCOE's can go to. The Dellorto DHLA 48 with 42 mm chokes is a way better carb at 5500 rpm, and produces a huge gain in performance. Only issue is that bigger DHLA 48's and 50's and Weber DCO 48's and 50's have always been mega expensive, and are race only items which have no cold start enrichment ciruits, which makes cold fouling even worse.
When doubled on a V12 LP400 Countach, six DCOE 45 mm Webers gave 375 hp at 8000 rpm, and less torque than DCOE40's. Imagine the torque with a 5340 cc Jag XK-E V12 with six HD8'S!
