The carb is also called the Varajet, and is French made half a 4M Quadrajet. It has been used on 1892, 2838 and 3294 cc General Motor Holden L4 and L6 OHV engines and the European J car Family II 1596 cc OHC 4 cyl engines from late 1978 to 1988. Its an amazing carb, but a little difficult to calibrate because of the a)hanger enrichment and b) rod selections. Jetting probably has to be sourced from RRP (Rochester Re Productions) approved sources, with the V6 and V8 jets too big for these carbs, or getting a jewler to recut a stock small jet to the bigger sizes with the right internal finish, and main hole and chamfer required to ensure the right flow. Jets are close limit, and carfully calibrated for each FMV/EPA/CARB/or ADR aproved engine combination.
Most of the hard performance work for an I-6 engine was done with the standard 114-121 hp carb applications for any GM 2.8 V6, GMH 2.8 and 3.3 L6. Holdens Aussie engines were very different, 76/78/80 hp in the 1892 cc ohv four, the J car 1596 cc 85 hp engine and 102, 114 and 121 hp in the 2838cc and 3294cc. The Rochester Varajet carb on ohv engines was a replacement for earlier single barrel Stromberg carbs, and yielded an extra 10 hp with ease, as well as a massive improvement in fuel economy. On these engines, there were porting changes and ignition system upgrades as well, but emissions were getting harder to pass each year, and 10 hp and about 1 second off the quater mile was a pretty good indication.
In terms of performance, they are neck and neck with the ADM34 carbs used in the Fiat Spyder/131/132 and the brace of 32/36 versions (Holley Weber 5200, 5210, 6500, the Bressel or Weber DGAS 32/36 or Weber DFA 32/36).