Dual-quad carb selection
Thread Starter
Instructor
Joined: Jun 2004
Posts: 235
Likes: 0
From: NE
Dual-quad carb selection
I’m thinking about edelbock’s dual-quad intake with their performer carbs. For the application on a bb 427 would it be better to have two 500, 600 or 650cfm carbs?
For a big block the edelbrock site recommends either two Performer 600cfm or two Thunder serics AVS 650cfm carbs. Wouldn’t either be too much? They would add up to 1200 / 1300cfm… Even two 500 carbs at 1000cfm seems like it could be too many cfm???
Here is the configuration:
BB 427, Heads: Afr 305
Cam: Crane Hydraulic roller 139731,
Basic Operating RPM Range: 2,500-6,000 RPM
Intake Duration 050 inch Lift: 226
Exhaust Duration 050 inch Lift: 234
Duration at 050 inch Lift: 226 int./234 exh.
Advertised Intake Duration: 288
Advertised Exhaust Duration: 296
Advertised Duration: 288 int./296 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.587
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.610
Valve Lift with Factory Rocker Arm Ratio: 0.587 int./0.610 exh. lift
Lobe Separation (degrees): 112
For a big block the edelbrock site recommends either two Performer 600cfm or two Thunder serics AVS 650cfm carbs. Wouldn’t either be too much? They would add up to 1200 / 1300cfm… Even two 500 carbs at 1000cfm seems like it could be too many cfm???
Here is the configuration:
BB 427, Heads: Afr 305
Cam: Crane Hydraulic roller 139731,
Basic Operating RPM Range: 2,500-6,000 RPM
Intake Duration 050 inch Lift: 226
Exhaust Duration 050 inch Lift: 234
Duration at 050 inch Lift: 226 int./234 exh.
Advertised Intake Duration: 288
Advertised Exhaust Duration: 296
Advertised Duration: 288 int./296 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.587
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.610
Valve Lift with Factory Rocker Arm Ratio: 0.587 int./0.610 exh. lift
Lobe Separation (degrees): 112
Last edited by Engraver; Feb 23, 2005 at 05:33 PM.
Drifting
Joined: May 2003
Posts: 1,634
Likes: 2
From: Melbourne, Victoria, Australia, the World
Ask Lars about having "Too Much" carburation. He is of the opinion that you can never have too much. If there are problems with stumbles and bogs they can be tuned out. 
Safety Car
Joined: Oct 2004
Posts: 3,924
Likes: 735
From: Youngstown Ohio
2 600 or 650 CFM carbs would not deliver "too much" cfm......I owned a (dare I say it ?) 1968 426 Hemi Roadrunner which came stock with this dual carb set-up....the progressive linkage only opens up the barrels as you need them or all 8 under full throttle only.
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
I feel dual carbs are for looks only. A good 850 double pumper will do all you want and be easier to tune. Dual carbs are dual trouble and a real pain since you need 2 sets of jets for everything.
That said I run dual 850 double pumpers on my blown 460 and still get about 15 mpg.
That said I run dual 850 double pumpers on my blown 460 and still get about 15 mpg.
Thread Starter
Instructor
Joined: Jun 2004
Posts: 235
Likes: 0
From: NE
Thanks for the help everyone.
I talked with edelbrock tech today and he recommended the two manual choke performer 600cfm carbs with an additional electric choke and placeing it on the rear carb.
I read their new AVS 650 is adjustable as to when the secondaries open up, but is there a way to adjust this in the performer carbs too? Does the performer have a spring on the secondaries that can be adjusted for how much vacuum it takes to open them?
I talked with edelbrock tech today and he recommended the two manual choke performer 600cfm carbs with an additional electric choke and placeing it on the rear carb.
I read their new AVS 650 is adjustable as to when the secondaries open up, but is there a way to adjust this in the performer carbs too? Does the performer have a spring on the secondaries that can be adjusted for how much vacuum it takes to open them?
Last edited by Engraver; Feb 24, 2005 at 12:36 AM.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
The Performer series uses a counter-weighted air door. The only way to tune the opening rate is to either remove or add weight. It's not impossible but it's not really convenient since the top of the carb has to come off to remove the door. If you're taking weight off to speed up the opening and you grind off enough to get a bog, then you have to find some way to add weight to get it in tune.
I suppose this was covered in your discussions with the tech, but there are different calibrations for dual-quad set ups. The idle and main air bleeds end up at least 70 percent larger to account for the airflow being shared by the two carbs.
And, no 650 (or 600) cfm is not too much. Ford used 715 cfm Holleys on their 427 dual quad set ups (and Shelby used the same on the 67 428 in the GT 500).
I suppose this was covered in your discussions with the tech, but there are different calibrations for dual-quad set ups. The idle and main air bleeds end up at least 70 percent larger to account for the airflow being shared by the two carbs.
And, no 650 (or 600) cfm is not too much. Ford used 715 cfm Holleys on their 427 dual quad set ups (and Shelby used the same on the 67 428 in the GT 500).
Safety Car
Joined: Oct 1999
Posts: 4,101
Likes: 10
From: NorCal
I have a pair of 500 cfm Carter AFB's on my 425hp/409. It's a stock progressive setup with a front primary and rear secondary. I don't have it running yet (need a car!), but Norval's right: they're more for looks and a single four barrel works better. Thats why the L-88 came with a Holley! A pile of carbs is sure cool, though!
Hans
Hans
