If everyone used a 4-bbl 4150 or 4160 series Holley, you could make any cam and intake system work. In some cases, a 2-bbl will have very poor perfromance and fuel distribution with I6's. The trick of opening the secondary throttles a little for airflow, and then adjusting idle mixtures and only drilling throttle plates if there is an idle to transition tune problem has worked for years on little OHC Pintos, Foxes and Rangers with 6299, 8007 and 6895 Holley 390 cfm carbs. You can run those on a 2 or 2.3 with the biggest cam, and they idle nice. The 350 or 500 2-bbl is very touchy with respect to cam timing, so are the bigger versions of the 2100 and 2150.
If you want to get the best out of a Holley, with none of the horrible split line and adjustment hassles, grab any old 7448 350 or 4412 500 cfm 2-bbl Holley, and run the Weber Power Plate (found used on the internet as Weber, Edelbrock or new from TMP Carbs).
Smaller venturis cost you power on a Holley or Autolite/Motorcraft 2-bbl. This is not true of DCOE Webers or dcnf or IDA and IDF down drafts, somtimes the venturi can be too big for the throttle. On the US Holley or Autolite/Motorcraft 2-bbls, the throttle bores and spacing can be nice and large, so the casting can support upsized venturis if the casting is epoxied or JBWelded to as much as 1.56" by fly cutting or 3M paper boring with a broom handle awl and drill, and the only issues that stop people making the bigger 1.21's and 1.33's work is air bleed, well tube, squirter, power vlave and and accelerator pump calibration.
Anytime you get better progression and economy with a sub optimal flow smaller carb is because its air fuel trim is out of wack. Running an smaller carb because you can't calibrate the bigger one for use when the bigger one has the right air flow is not the smart way to go. Again, the way they come prepared, none of the 2-bbl Holley/Autolite/Motorcraft carbs like large duration cams, its very easy to get fuel standoff and reversion problems, typical of the smaller i6 with big cams and automatic gearboxes with stock 1650 stall ratios. They have multiple problems with distributor calibration being out, cam being to big, stall being to low, and then the owner dropping out of a bigger carb to a smaller one.
The kits have been around since the early 80's. It has long gone out of major US production from Edelebrock and Weber, but new from TMP, it is expensive, and there are some debates about how ideal the Weber IDA well tubes are in a Holley application, but they work, and can make a seamless Air Fuel ratio.
That allows you to run bigger venturis, and the Autolite/Motorcraft venturis cost you power at 1.08 to 1.21 inches. A 500 Holley with 1.375" venturi or
a 650 series 2-bbl venturi size of 1.4375 with an upsized 1.75" throttle can be operated with ease when you use this kit.
You get two plates in the kit because its generally for 4150 or 4160 4-bbls, but you only need to run the one with the accelerator pump
70 idle jet, 150 air corrector,
155 main jets, 110 air correctors,
Two IDA F11 emulsion tubes
and a 120 micron Power Valve Channel restriction will make the engine run clean and responsive.
Emulsion tube is based on hp level expected, intake runner type, and the venturi size, but the five emulsion tubes cover that off.
That will get you started.
It allows you to carb to a better, bigger carb size, but has a transition circuit, and there is now the right access and info on 61450xxx Weber emulsion tubes and main jets and air correctors.
Most importantly, you can run a standard high pressure fuel pump, and even change idle jets with the engine running. Its set up for a standard Holley float height, but has been used in competition Cleveland race engines for years down in Australia, and it eliminates all the hassles of the truly awful vertically jointed Holley float bowl.
In an i6, the throttles can be run parallel to the crank, and then the power valve will never be uncovered under acceleration. The float level isn't optimal with the stock five kinds of 61450 series IDA emulsion tubes, but that's irrelevant because the choices work for the power levels, fuel pressures and float levels you's see from a front float bowl.
http://speedtalk.com/forum/viewtopic.php?f=1&t=33417
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