Re: Re: Carb adaptors- 4bbl to 2bbl ?

Posted by Jon Hagen on December 15, 2007 at 12:23:44 from (12.175.230.37):

In Reply to: Re: Carb adaptors- 4bbl to 2bbl ? posted by JerryCPP(WA) on December 15, 2007 at 06:12:58:

There are many style of adapters avalible. Some center the 2 bbl over the center of the 4bbl carb flange, some center the 2bbl over the primary barrels of the 4 bbl flange, some have a big open plenum, some have a closed two hole plenum for more ram effect at part throttle.

The 2 hole plenum centered over the primary end of the 4 bbl flange will give best fuel economy.

You might want to rethink that 2bbl VS 4 bbl thing though, In most cases a gently driven spread bore 4 bbl( like the GM quadrajet) with it,s tiny primary barrels made better fuel economy than the consideribly larger barrels of the same engine with a two barrel carb. The tiny front barrels of a spread bore 4bbl, had more air velocity than a larger 2 bbl at low power loads,so were more efficient at mixing gasoline and air. I know people that disconnected the linkage to the huge secondary barrels of a quadrajet,so it would operate only as a tiny 2 bbl carb, which made them a real economy champ. Some of the smaller GM V6 and V8 engines came equipped with a 2 bbl carb which was basically just the front half of a Q jet 4 bbl.

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