General Category > Quadrajet Carb Talk and Tips

2x4 Oldsmobile 455

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Marx3:
just checked with my buddy. The linkage on a factory 2x4 Nailhead is working like you described Von. That is the way to go.
I guess both carbs would have to be equally jetted somewhat leaner than in a 1x4 setup... ?

Cliff Ruggles:
No, it doesn't work that way.  They would need the correct jetting and would not need to be leaner simply because there are two of them, as they don't run richer because more than one is being used.

The idle system typically needs attention, as you are doubling up idle bypass air, so we don't use any and use both carbs at idle for dual quad applications.....Cliff

Marx3:
you dont say... I dont fully understand why this is. The engine does not ingest more air just because there are 2 carbs, but since there are twice as many venturies, the engine would have twice as much fuel available... Why does it not work that way?

I will be fine tuning the afr with my wideband, so I will get a good afr no matter what.
Nice to know about the idle. This makes sense, though :-)

HeathD:
Im guessing that the air drawn in will only be as much as the engine can pull and because of this the carb will only supply that amount of fuel/air mix.   Just because it could use twice the fuel as a single carb doesnt mean it can use it.

I'm picking the idle set up and transition to secondaries will be the biggest hassle.   Getting them balanced and not fighting each other will be a challenge (or maybe not I'm guessing again).   I guess it will be like driving a 4 barrel carb with 4 massive secondaries so the primary circuits will be restricted a little to get the best out of the pair (and try to get some fuel economy back - yeah, probably not, but the cool factor will make up for it).

Will the secondary springs need to be wound back so they both open at lower vacuum or left std?

I'm watching this thread with interest as it looks to be a real head turner.   Dont forget some pics when you are done.

Cliff Ruggles:
I really don't have the time or space to go into the "science" of what's going on with 2 x 4 set-ups.  They will not need "leaned up", just set them up correctly as if you were only using one of them, and tune from that point.  They will need more attention to the idle system than the main system, as airflow thru each one at idle speed is very low compared to only using one carburetor......Cliff

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