Secondaries
Thread Starter
Safety Car
Joined: Aug 2002
Posts: 4,812
Likes: 1
From: New Albany IN
St. Jude Donor '03-'04-'06-'08-'09
Secondaries
Did a search but couldn't find the advice.....
mild built 350 with 280 magnum cam...4 speed..
vacuum or mechanical secondaries best?
mild built 350 with 280 magnum cam...4 speed..
vacuum or mechanical secondaries best?
Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I have the Magnum 280 cam w/4-sp and have run it with the stock Quadrajet, Holley 4011 650 w/vacuum secondaries and currently with a Holley Street HP 650 w/mechanical secondaries. Hands down, the 650 Street HP is the most responsive and has more seat of the pants power.
Thread Starter
Safety Car
Joined: Aug 2002
Posts: 4,812
Likes: 1
From: New Albany IN
St. Jude Donor '03-'04-'06-'08-'09
I have the Magnum 280 cam w/4-sp and have run it with the stock Quadrajet, Holley 4011 650 w/vacuum secondaries and currently with a Holley Street HP 650 w/mechanical secondaries. Hands down, the 650 Street HP is the most responsive and has more seat of the pants power.
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Got a Crane Energizer 272H cam setup. My qjet rocks! If you are leaning toward originality, You may want to refresh the q'jet. It is VERY responsive when calibrated to your installation. Minor primary and secondary metering rods and primary jets adjustment (if your qjet is otherwise healthy) and you WILL be surprised.
I miss Lars' input...
I miss Lars' input...
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
In case anyone is confused about it, the Q-Jet secondaries are mechanical. Depending on its configuration, there may be either a vacuum or a mechanical 'limiter' that prevents the secondaries from opening when they should not, but if the engine is warmed up and functioning properly, the secondary throttle plates open completely with WOT demand. Yes, there is also an airvalve at the entry to the secondary venturi, but if properly adjusted, that just makes an optimum transition from a 'low power' to 'full power' condition; it does not reduce engine performance. That airvalve also allows the Q-Jet to work for nearly any sized engine without major modification to the carb (as long as the engine airflow requirements do not exceed the maximum capacity of the carb).
When properly set up, any good carb will produce nearly equal "WOT performance". But, doing that as well as operating efficiently during "daily" operation is something the Q-Jet can do that most others cannot.
When properly set up, any good carb will produce nearly equal "WOT performance". But, doing that as well as operating efficiently during "daily" operation is something the Q-Jet can do that most others cannot.
Last edited by 7T1vette; Jan 24, 2012 at 10:42 PM.
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Had a 1976 L-82, 4-sp
Joined: Mar 2011
Posts: 5,338
Likes: 1,213
From: Some days your the dog and some days your the hydrant.
Royal Canadian Navy
I also have the M21 close ratio and 3.55 rear. The carb sits on an adapter plate on top of a spreadbore Edelbrock Performer intake (1995 vintage). I will soon be removing the intake and heads and replacing them with AFR 195 Street Eliminator's and a Weiand Team G single plane intake. Can't wait to try that out! Next year I will install a roller cam and in a few years more a 427 small block. I'm not concerned with originality, price of gas nor gas mileage as the car is a weekend only driver.