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What carb for my setup?

  • Rebuild the 750 Qjet?

    Votes: 21 53.8%
  • Holley 670 Street Avenger?

    Votes: 10 25.6%
  • Holley 750?

    Votes: 8 20.5%

  • Total voters
    39
  • Poll closed .
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Discussion Starter #1 (Edited)
So here's the issue!
I swapped from the old 355 last year to this Kim Barr Racing 383 last May and I need advice on choosing a good daily driver carb.
The engine was originally tested and outfitted with a Holley 750 DP,but the PO removed it and installed a 600 Edelbrock.
The Edelbrock carb was terrible since I needed starting fluid to start the car every time it sat overnight and it always ran lean. After enough of playing with that POS,I installed my Q-jet and got my mpg's back and had an easier time with my car.
I'm looking to either rebuild or change the carb due to the bogging [email protected] and mpg improvement.(yes both fuel filters are clean)
Whats are my options?
Rebuild my 750 Qjet,Holley 670,or Holley 750?
This car is a daily driver with occasional track/race time since its more of a sleeper.
Will downgrading to a Holley 670 improve mpg's while gaining performance or do I go with a Holley 750 since that's what this hot rod engine originally came with?
I want to also feel my secondaries like the Q-jet.
I've yet to see a performance engine with a stock Q-jet on top of it like mine...:dontknow:
(The Qjet has never been rebuilt since I had the car.(3 1/2 years)
 
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Discussion Starter #2
Forgot to mention it has a mild cam,2400-2600 stall.
 

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My GM crate engine came with the Holley 750 Dbl pumper.

With the dual plane manifold it is incredibly responsive when you get on it .

You're at 5400 rpm in a heartbeat with the 700R4 and 373 posi.

At 10 MPG not the most economical daily driver though.

Arnie
 

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I know you and more importantly I know how you drive, unless you put a brick under the gas petal
you’ll never get good gas mileage!!!!
I have yet to own an El Camino that you don't want to race and I swear an old lady can pull up beside you at a stop light to fast and, (the race is on!!)
Performance you can get but fuel economy? Not unless you cut your right foot off!!!:poke:
Donny
 

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I say go with getting the Q-jet rebuilt by that guy that everyone sends them to (forgot his name).

:poke:
 
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Discussion Starter #7
Todd is pointing me towards the 750 Holley. I have the dual plane intake btw.
 

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The Holleydp designwill have more top end response, but by design kill your daily mileage. You could get the quad running right &swap on a 750dp for special occasions. If you don,t have a holley specifically tuned for your motor,you,ll have to get it dialed in correctly also, they are more fussy about needing tuning.
Haven't cracked open a quadrajet in over 20 years, but I,m thinkin yours may need larger secondry jets or metering rods. Our EDONTHEBEACH , my video guy, did a 2 part video on rejetting a quadrajet. Haven,t watched it , but it may help.
 

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i have run and tweeked both carbs. my favorite for big hp is the holley, but the right q jet and the right work to it and the q jet will be very close in hp and way ahead in fuel mileage and driveability.i use the later big q jet with the lean stop adjustment, to prevent over lean on a race preped engine.use the right use the right pri and sec jets and metering rods and the right sec hanger.adjust the sec acturator arm a little sooner and put about 3/16 slop in the sec air valve rod adjustment and it should be great on a real healthy 383 with a small converter. i am asumeing you have a small amount of gear?
 
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Discussion Starter #11
I know you and more importantly I know how you drive, unless you put a brick under the gas petal
you’ll never get good gas mileage!!!!
I have yet to own an El Camino that you don't want to race and I swear an old lady can pull up beside you at a stop light to fast and, (the race is on!!)
Performance you can get but fuel economy? Not unless you cut your right foot off!!!:poke:
Donny
So says the one who didn't slow down until they got a 305?:poke:
 

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Your Qjet is a spread bore style carb. Although Holley does sell a spread bore model, their carbs are a square bore design. That being said, the Holley will not fit your manifold without using a adaptor.
 

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The Q-Jet is one of the best carb designs out there. The main problem is that they are very application specific. If you can get that Q-Jet tuned correctly I think you will be much happier than using a Holley.

~JM~
 
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Discussion Starter #15
I wanna experience the Holley but,another member reminded me that a Holley will continuously dump fuel while the Q-jet will only dump what my engine needs.
 

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You put your right foot in, you watch your gas drop,
That’s what it's all about!!(Hokey Pokey) song!!!:nanawrench:
Lead food, you got 2 feet but both or on the right!!!:poke:
Donny
 

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if the holley is good it shouldnt just dump fuel, the engine sucks the fuel out of the carb no matter what kind of carb it is.a holley is a good carb but not as effiecient as a good q jet. they were designed for power more so than fuel milage.trust me on this a bad q jet can waste as much gas as a bad holley.
 
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Discussion Starter #18
So getting fuel efficiency and power,the Q-jet is the correct carb? How much power would I be losing if the Q-jet gets a stock rebuild compared to a 750 Holley?
 

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As stated above it will all depend on how well either one is tuned properly for your engine. I don't think you would gain enough from the holley at wot to offset the benefits of the q-jet. JMHO Stay with the q-jet.
 

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that is a loaded question without knowing the engine its really hard to say.to be fairly accurate i would need all of the info from both carbs and engine details,what jets and metering rods ,sec hanger #. but genarally between 3 and 10 % hp differance between a properly set up holley and the same properly set up q jet. there are so many variables with each carb. if i am going to use a stock build q jet on a 383 i use the one from a 454. the ones set up for a 350 may be a little lean and dont have the better idle transition circuits mods to feed the bigger motors
 
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