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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 81_Chevy on December 24, 2012, 07:04:48 pm

Title: Carb ?'s
Post by: 81_Chevy on December 24, 2012, 07:04:48 pm

my cousin has a couple of Holley 550's laying around in his shed back from his stock car days. hes gunna let me have both of them for christmas and let me keep the better of the two. i have a stock 350 with a q-jet. i know the q-jet is around 750ish cfm and the holley is 550. my question is for you guys will the 550 be enough to power my 350 and in your opinion which is the better choice (performance wise and mileage wise). im not looking to get extreme power, more fuel mileage that anything.

-Nic

Title: Re: Carb ?'s
Post by: ralphhemi on December 24, 2012, 07:47:25 pm

i had a 1977 350 with a Q jet on it and replaced it with an adapter to install a 500cfm. Holley 2 barrel and ended up with a ton of low speed torque   

Title: Re: Carb ?'s
Post by: 81_Chevy on December 24, 2012, 08:53:14 pm

i believe these are 4 barrels

Title: Re: Carb ?'s
Post by: square81 on December 25, 2012, 12:51:00 pm

If there isnt anything wrong with the Q jet and the truck runs good, I'd just leave it alone. If the 550 is from his racing days it's likely made for all out performance. Maybe not good for economy.

Title: Re: Carb ?'s
Post by: 81_Chevy on December 25, 2012, 04:25:06 pm

he said that they are both stock

Title: Re: Carb ?'s
Post by: VileZambonie on December 25, 2012, 05:55:03 pm

The Qudrajet is the better option.

Title: Re: Carb ?'s
Post by: 81_Chevy on December 29, 2012, 09:13:20 pm

anybody else?

Title: Re: Carb ?'s
Post by: 454Man on December 29, 2012, 09:16:05 pm

Qjet

Title: Re: Carb ?'s
Post by: Irish_Alley on December 30, 2012, 10:29:29 am

 gm did limit the air flow on the carbs to match the engine so if your engine cant handle all that cfms the secondarys wont open all the way. this is how your 750 cfm can be used on a sbc and bbc. a mild 350 shouldnt use 600cfms.

Title: Re: Carb ?'s
Post by: Captkaos on December 30, 2012, 12:04:57 pm

Quadrajet, hands down for economy.

Qjets are vacuum operated secondaries, it will only pull in what it needs.  The airvalve and choke pulloff limit the amount of air to only what the motor can pull in. 

Title: Re: Carb ?'s
Post by: 81_Chevy on December 30, 2012, 06:31:15 pm

could anybody tell me how to tune my q jet then? the last guy that did it did a horrible job, it hasnt run right since he rebuilt it. im getting about 5-8 mpg and i have literally no power when i put my foot to the floor.

Title: Re: Carb ?'s
Post by: Irish_Alley on January 06, 2013, 08:55:19 am

http://www.crankshaftcoalition.com/wiki/How_to_rebuild_a_Rochester_Quadrajet_4MV_carburetor