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Holley 4779 with weird iab
Posted:
Wed Apr 19, 2023 11:55 pmby 1969Camaro
This carb started life at a big rebuilder and then I think another person did some drilling.
The new down stream IAB exits in the Venturi via the new hole drilled and then epoxy covered.
Why??
Re: Holley 4779 with weird iab
Posted:
Wed Apr 19, 2023 11:57 pmby 1969Camaro
Main body side
Re: Holley 4779 with weird iab
Posted:
Thu Apr 20, 2023 12:33 pmby rgalajda
Used only with auxiliary idle air bleed. # 5 on picture below.
I can only assume this was a trial and error experiment someone tried on the carb you pictured.
Some of the OEM Chevrolet Holley carbs had a lower idle air bleed drilled in the main venturi ( similar to quadrajet carbs ) The 1969 427/425 HP Holley carb had this. Idle air fuel ratio was in the 14.5:1 range. I have experimented with this on my car. Since my cam has more duration and tighter LSA , this made the idle air fuel ratio too lean for it to idle .
As noted #5 in the picture . I have yet to see a holley carb with this passage used. So I don't know the application .
Re: Holley 4779 with weird iab
Posted:
Thu Apr 20, 2023 2:23 pmby 1969Camaro
Why would someone do this and what is the advantage? Btw, the idle feed restrictors are in the upper position.
Re: Holley 4779 with weird iab
Posted:
Thu Apr 20, 2023 5:20 pmby rgalajda
For a mild cam engine this could correct rich AFR in the low throttle opening if you drilled the right size. ??????
Same reason the cut the air horn/choke off . They thought better air flow. Generally it does not help.