Easy, this one.
Block off the power valve, and don't use a jet with a discharge of less than 1.85 mm or 0.073 thou or 450 cc/min firstly. That's only enough to make 180 hp with it. In Holley numbering, its a 70 call size jet. Anything less will burn baby burn a cylinder.
On the basis of choke size with most Bendix Stromberg XY-XD 250 carbs, I'd say a 550 cc/min flow rate jet would do magic. A Holley 74 or 75 call size or drilled out duplicate would suffice.Any drilled out jet has to be chamfered and tested to match its neighbour, or fuel air ratio will go haywire . Check flow rates with an EFI pump at 80 psi for one minute into a graduated glass beaker
For Holley 2300/4150/4160/4180 jets the rates are:-
448 cc/min or 73 thou nominal, 70 call size jet
470 cc/min or 76 thou nominal, 71 call size jet
492 cc/min or 79 thou nominal, 72 call size jet
517 cc/min or 79 thou nominal, 73 call size jet
542 cc/min or 81 thou nominal, 74 call size jet
566 cc/min or 82 thou nominal, 75 call size jet
587 cc/min or 84 thou nominal, 76 call size jet
615 cc/min or 86 thou nominal, 77 call size jet
645 cc/min or 89 thou nominal, 78 call size jet
677 cc/min or 91 thou nominal, 79 call size jet
703 cc/min or 93 thou nominal, 80 call size jet
I've got all log heads from 1961 to 1983 which I'm busy gasflowing on my customade electronic flowbench. And all cross flow heads from the early iron XC to the 1983 Alloy head II.
If it runs the ARC9DE 6049 B head, it'd work fine as a simultaneous triple set up, but you'd be 60-80 hp down on three 45DCOE carbs with a 2v head.
Have a look at
viewtopic.php?f=1&t=64712
Kevins wild 1961 200 Falcon with triple Weber ICT's, he made what he said was 177 hp, but I've calculated to be 181 flywheel hp net at 5100rpm with 29 mm venturis, a 264 degree cam, and the best Offenhauser intake and 1978 log head. Torque was 204 lb-ft at 3500 rpm.
He used 190 micron outer and 175 micron inner Weber jets, which average about 500 and 450 cc/min. They are 1.9 and 1.75 mm, or 0.075 and 0.069 thou jets, equal to 72 and 70 call size Holley jets.
In your case, the hp would level off at around 220 with at 4800rpm with a 250, and you'd have to look at jets that would discharge quite a lot more than the stock Falcon 1-bbl jets. You'd be lucky to get past 260 lb-ft at 3500 rpm. It would yield 4 litre EB XR6 performance with a not a lot more fuel used. There is the possibility that due to intake and exhast flow, the 250's long stroke and a rod ratio just like the US 200's, that it might not even make 200 hp with an ARc9de head.
First, remember that three XD Falcon carbs have a power range from 102 hp net in the low compression iron head 3.3, to 140 hp net in the non emissions F100/NZ spec High Compression alloy head 4.1. So in theory, three carbs would be adequate for 306 to 420 hp. XY 1-bbl carbs vary from 3.3 to 4.1, with 125 to 155 hp gross, which is 108 to 134hp net, so would in theory be 324 to 402 hp as a triple carb set-up.
Sadly, as a result, the accelerator jet, idle jet, main jet and power valve will need recalibration to suit the reduced wetted perimeter of three carbs feeding just two cylinders each. Power valve will have to be made non functional, the accelerator jet will have to have a third less discharge, main jets might have to be made bigger , and idle jetting will need to re-set.
Any XY to XD 1-bbl carb is designed to give fuel to cylinder 1 and 6 which are 24 inches apart, and at least 1.3 inches in diameter. Median distance between cylinders is 4.08", distance of each branch is about 4", and the resulting wetted perimeter which fuel can adhear to is a stunning amount, about equal to a 72 inch long tube of a 1.3 inch diameter. In square inches, the area is over 70 square inches for only about 9 square inches of port. Most of the fuel in a 1-bbl six is therefore wasted as condensed, puddled mixture, and along with the time of concentration for getting the fuel mix from the carb to cylinders 1 and 6, this is the main reason 1-bbl sixes are so bad a making good specific power in comparison to V8's.
When anyone just adds two properly calibrated carbs, it improves power via reduced wetted perimeter, and by equalising flow efficency. In difference to six pack V8's, in case of all triple carb installations on I6's, its best not to run a progressive linkage as progressive linkage systems suffer extreme rich to lean conditions before, during and after the outer carbs open.
If you used that almost 300 degree cam on a triple Weber 45 DCOE equiped Falcon 2V with six 38 mm venturis, you'd expect about 280 hp net at 5200 rpm. Three Falcon Bendix Strombergs are only 1.25 inch venturi carbs and are like running three HS4 SU carbs of 1.5" diameter, so the power is no different to 3.5 Rover with twin CD175's, or a Jag XJ6 with twin 2" SU's. Or like adding 64 cubic inches to a stock GTR186 with CD150 carbs and then putting an XU1 202 cam in it. That's why I say you'd be very lucky to result in more than a maximum of about 220 hp at 4800 rpm.
