How does a blow through carb work? - Ford Mustang Forums : Mustang Forum
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post #1 of 5 Old 06-23-2003, 04:47 PM Thread Starter
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Question How does a blow through carb work?

Why doesn't the float bowl get pressurized through the jets? Is a special carb needed? I was just wondering.
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post #2 of 5 Old 06-23-2003, 08:11 PM
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I don't know how to answer your question regarding the float bowl getting pressure through the jets, but I am using a blowthrough carb in my combo. It's a Speed Demon 750 inside a Vortech Carb enclosure. The only mods other than jetting were the high speed bleeds that I tapped into the carb. If you use an enclosure you don't make any mods other than tuning, but if you use a carb hat you will need to modify the carb otherwise it will not work properly. If you have specific questions about what mods are done you can contact the Carb Shop at

Good luck,

1990 Mustang LX with a carbureted Vortech Mondo blown 408...

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post #3 of 5 Old 06-23-2003, 08:51 PM
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If you use a carb enclosure like Fasttoy you can pretty much use any out of the box carb. If you use the carb hat you are going to have to modify the carb to work with boost being forced into it. The throttle plate shafts have to be modified etc.. etc.. so there are no places for the pressure to escape. On a roots supercharger none of these carb mods are needed since the supercharger is after the carb. If you need a list of what has to be modified for the carb hat I can dig it up for you.
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post #4 of 5 Old 06-24-2003, 12:28 AM
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I run a blow thru and I just bought a 670 Holley Street Averger. I had to replace the floats with the black ones and rejetted, thats all I did. I've been running this set up for a year now without a problem.

65 chrome yellow GT...306 w/T5
SMI Custom carb
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Crane 2031 SC roller cam
TFS 1.7 Rockers
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post #5 of 5 Old 07-20-2003, 12:48 PM
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Your float bowls are pressurised through the bowl vents at the top of the carb................If you were to block the vents then fuel would not flow from the jets because the boost would only be in the venturi
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