what are "secondaries"?
what are "secondaries"?
FTE Chapter Leader
Joined: Sep 2000
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From: Beachville, Ontario
In a 4 barrel carb, it usually runs using 2 barrels under "cruise" conditions, under heavy load (like when you mash the loud pedal) the other 2 barrels will open up, these are the secondaries. Vacuum secondaries are controlled by engine vacuum levels, mechanical secondaries are controlled by the throttle linkage/gas pedal. Most carbs also have a mechanical set of throttle blades in the secondaries in addition to the vacuum controlled throttle blades. Vacuum secondaries are usually recommended for a street driven vehicle, I believe this is because it is more responsive to engine load and makes the driveability of the vehicle better.
I hope this helps explain it a bit to you and I haven't confused you.
I hope this helps explain it a bit to you and I haven't confused you.
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Joined: Apr 2000
Posts: 2,838
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From: SD
This is only on 4 barrel carbs. The front two barrels (holes) work toghether and the rear two work together. The front is primaries and the rear is secondaries.
Mechanical secondaries are connected directly to the throttle and are manually opened as the throttle is moved. With vacuum secondaries, the secondaries are controlled by a engine vacuum. When the carb senses it needs more power (when you hit the throttle) it will open the secondaries.
Mechanical secondaries are for high performance motors and racing. They tend to cause a 'bog' off the line and are best for vehicles with high stall converters, not daily drivers.
Vacuum secondaries are more gradual opening which eliminates the 'bog' felt with mechanical ones. Vacuum secondaries are best for a daily driver or manual transmission. If you don't have a high stall converter or run quarter mile track - stick with a vacuum secondary carb, you will be much happier and your vehicle will be much more driveable.
Almost all Edelbrock and Carters are vacuum secondaries, Holley makes a lot of both. What vehicle are you looking to get a carb for?
Marty
Mechanical secondaries are connected directly to the throttle and are manually opened as the throttle is moved. With vacuum secondaries, the secondaries are controlled by a engine vacuum. When the carb senses it needs more power (when you hit the throttle) it will open the secondaries.
Mechanical secondaries are for high performance motors and racing. They tend to cause a 'bog' off the line and are best for vehicles with high stall converters, not daily drivers.
Vacuum secondaries are more gradual opening which eliminates the 'bog' felt with mechanical ones. Vacuum secondaries are best for a daily driver or manual transmission. If you don't have a high stall converter or run quarter mile track - stick with a vacuum secondary carb, you will be much happier and your vehicle will be much more driveable.
Almost all Edelbrock and Carters are vacuum secondaries, Holley makes a lot of both. What vehicle are you looking to get a carb for?
Marty
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From: Honkytonkville
Oh, I'm not looking for a carb, just never referred to "secondaries" as "secondaries", I always called them 'the front barrels'(the front are the secondaries, correct? I can't be sure without looking at it) Just never knew what the term directly referred to. I actually did know everything you guys just told me, just I didn't have the terminology down....Thanks guys!
Scott
Scott
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From: Honkytonkville
Are you sure? Maybe Q-jets(yeah, on Chebbys i know sorry sorry) its backwards, or I was misinformed....I was told in a Qjet the engine runs on the smaller barrels until you get on it then the big barrels kick in....
Scott
Scott
Last edited by scottie2hottie; Nov 4, 2004 at 05:36 PM.
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From: Honkytonkville
I don't have the car with the Qjet here, so Im not sure off the top of my head where the big barrels/small barrels are for sure(aka I could definitely be wrong). It's on my derby car motor(350 ci), which I keep at my buddy's shop. It has a Qjet intake manifold, but an adaptor plate with a Ford 2 barrel on top. Qjets are junk and can't take a beating like the Ford 2v, and wow, what a difference in throttle response!
Scott
Scott
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From: Louisville,Ky.
The rear (larger ones on the Q-Jet) are the secondaries.
Just a note, Edelbrocks and Carters are mechanical secondaries. They (like the Q-Jet) use a air flap valve on the top of the carb to keep it from bogging down when the rear barrels open because there is no accelerator pump on the secondaries.
Just a note, Edelbrocks and Carters are mechanical secondaries. They (like the Q-Jet) use a air flap valve on the top of the carb to keep it from bogging down when the rear barrels open because there is no accelerator pump on the secondaries.
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