Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Dual quads

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chance:
Hello, just joined  the forum. I just bought cliffs book on rebuilding and modifying q jets... lots of good info awesome read!! It didn't have any info on dual quad applications so I'll ask here. the carbs will be going on a mopar 383 with 10 to 1 compression flat top pistons with no valve reliefs  906 heads with steel shim head gaskets , offenhauser 3614 low risedual quad intake. Engine pulls between 7 and 8 inches of vacuum. I have several carbs to work with. Just wondering about idle and main jetting, and choke pull off time in this application.
Thanks guys!
God bless!!!

Cliff Ruggles:
Not enough information.  Need to know the carburetor number(s), and camshaft specifications.  One q-jet would be more than enough for that engine, but they work fine using two of them even though it doesn't need no where near that much cfm due to the design of the secondary system.

I've set up quite a few for dual quad applications.  The best carbs to start with are Chevy side inlet units with the divorced choke set-up from 1969 to 1977.  For sure it is best to find two with the same part number, but not a requirement.....Cliff

chance:
Thanks Cliff. I'm currently building an 800 cfm single q jet based off of your book. it will sit on  a single plane Mopar M1 intake that's on the car now with a 750 holley. I ran the dual quad manifold for a while with 2 450 holleys but the et's went down by 4 to 6 tenths so I went back to the single holley as I could never get a q jet to perform correctly with that cam. I have a bunch of q jets that the haters club has given to me over the years and I buy them at swap meets for little or nothing. I would like to try the dual q jets because a friend of mine has a Buick Riviera with a factory 425 with 2 q jets and its the best running dual quad set up I have ever driven, it works well on the street as well as the drag strip. Any ideas on main jets and rods and choke pull off for running 2 of them?
I love your book! Found out a lot I didn't know about q jets and I've been rebuilding and running them for years.
Take care and God Bless!!!

Cliff Ruggles:
I owned, drove and drag raced a 1970 Roadrunner for many years.  Started out with a 383 and rebuilt it with the Mopar 284/484 cam.  I tried several intakes on it over the years and it ran quickest in ET with a stock spread bore intake topped with an 800cfm q-jet.

I ran the factory square flange intake with an 850DP Holley and it was close in ET but less MPH due to the smaller plenum area.

I tried several single plane intakes on it and it really slowed the car down.  I was running a 3000 stall converter and 4.56 gears in it.  Probably needed more converter for the single plane intakes because it "felt" stronger at full throttle, but the time slips showed that it really slowed down in 60' times.

I ended up replacing the 383 with a 440 and it ran half a second quicker at the track with the same basic set-up.

chance:
That's awesome! Almost identical situations, I have a 68 charger B body, same engine, 3500 stall 4:30 gears. The only reason I never went with a dual plane manifold is a buddy of mine had a 66 cornet with a 440, 484/284 purple shaft cam and the mopar M1 dual plane manifold 3000 stall converter 4:10 gears, and my car was always quicker than his. His 60' times were quicker, 1/8 mile was within couple hundredths, 1/4 mile I'd take him by 3 to 4 tenths. So the stock iron dual plane worked best for you? I don't think I have any of those any more...lol. Guess Ill try to round one up.
Thanks Cliff!
God Bless!!!

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