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Old 04-25-2012, 03:58 PM   #1
Scottd
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Default Can I use a square bore carb on spread bore intake?

Ive got a 'Brock spread bore intake on my big block and a 'Brock 1407 carb. (I think its the 1407, standard run of the mill Brock 750 cfm 4bbl) This was how it was set up when I got the car. In order to cure some carb heat sink issues, I installed a spacer/squarebore-spreadbore adapter. The ones Pepboys sells, they are about 3/4 inch thick. Im looking to go to a Holley Avenger as soon as I get home from my deployment (Hello from Kuwait, BTW) and I want everything to work to its optimum potential. I know adapters are made, but is there any performance lost or gained from this setup? Should I swap over to a square bore, run the adapter, or just bolt it on? (The Holley to the spread bore intake) I dont want to dig too deep into the motor yet, but I want to make sure Ive got everything in synch before I decide how much of an upgrade I want to sink into this when I get back.
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Old 04-25-2012, 04:01 PM   #2
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any adaptor that goes from one type to another will be a compromise. Get the correct combo of carb and manifold. Good luck.
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Old 04-25-2012, 04:48 PM   #3
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The only square bore carbs I see (that Id spend the money on) are Summit remanufactured Quadrajets. I dont know ANYTHING about Quadrajets and have heard they can be problematic. Are they easy enough to work on or sould I just stick with a Holley Avenger and change out the intake manifold? (I dont want to get rid of a perfectly good intake if a Quadrajet can be tuned to run like a Holley)..
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Old 04-25-2012, 05:56 PM   #4
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The slobber jet is a GREAT carb....when it is on it's awesome have you seen those freaking pop can size secondaries.....geez. Are they as reliable as a Holley, sorry no they aren't. I would try the rebuilt or find a Q-jet guy, usually there is someone around with skills to tweek an old Rochester back to life....
By the way Thank YOU for your service be safe in the sand.......
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Old 04-25-2012, 09:29 PM   #5
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Not really. There is no "good" way to interchange parts between squarebore and spreadbore carbs/manifolds. There are "adapters" which you can buy...but they only allow the carbs to function with the 'wrong' manifold. They won't work properly or well....
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Old 04-26-2012, 12:38 AM   #6
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Quote:
Originally Posted by Scottd View Post
The only square bore carbs I see (that Id spend the money on) are Summit remanufactured Quadrajets. I dont know ANYTHING about Quadrajets and have heard they can be problematic. Are they easy enough to work on or sould I just stick with a Holley Avenger and change out the intake manifold? (I dont want to get rid of a perfectly good intake if a Quadrajet can be tuned to run like a Holley)..
Q-Jets are spread bore.

The only problematic Q-Jets are those that have been hacked up by morons.
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Old 04-26-2012, 03:30 AM   #7
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Q-Jets are spread bore.

The only problematic Q-Jets are those that have been hacked up by morons.
So Im faced with either swapping the intake and the carb, or buying a rebuilt quadrajet. So I have a few questions about the quad. 1) Will it be bolt on and go like a Holley? 2) How easy are idle and mixture adjustments 3) are their any easy ways to fine tune it for the average street car? and 4) when someone says they arent as reliable as a Holley, what do they mean? Are they as responsive? Thats my biggest concern. The Avenger on my camaro is ultra responsive and all I did was replace the acc pump spring.
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Old 04-26-2012, 08:47 AM   #8
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I wouldn't buy a commercially rebuilt Quadrajet. Been there. It was a piece of junk. If you decide to go with a Quadrajet, look for one which hasn't been touched by a commercial rebuilder. I bought one a while back from a fellow on this forum. Lars gave it a once over for a very reasonable fee. Like day and night, ran MUCH better than the commercial rebuilt POS.

Otherwise, as much as I like my QJet, you could buy a new Holley if you are concerned with issues dealing with used QJets. Either carb may require some tweaking for your specific application.
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Old 04-26-2012, 04:08 PM   #9
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Are there any distinct advantages to a spread-bore setup?

I really dont want to buy another intake manifold if I can avoid it, so I guess Im stuck running a spread bore for now. Summit sells Quadrajet rebuilds for 300, and I see Holley makes a spreadbore model for around 400. What else are my options, staying under the 400 dollar realm?

Does Lars still do carb work? (Forgive me if Im asking a taboo subject here.....)
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Old 04-26-2012, 04:23 PM   #10
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I think you shoud do nothing to the existing set up as long as it is driveable. Once you are in a position to do more work get a standard bore intake and a suitable carburetor. Any spread bore you buy now you will end up trying to sell once you make more changes.
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Old 04-26-2012, 04:34 PM   #11
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Quote:
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I think you shoud do nothing to the existing set up as long as it is driveable. Once you are in a position to do more work get a standard bore intake and a suitable carburetor. Any spread bore you buy now you will end up trying to sell once you make more changes.
Why is that? Ill have the money to spend, I just dont want to spend it if its unnecessary. I detest Edelbrock 1400 series carbs because of the horrible heat sink/vapor lock problems Ive had with them. I also hate running adapter plates to counter heat problems and carb/intake pattern differences. If Ill ultimately be happier with a square bore carb and intake, Im all ears to hear why Ill be disappointed with a quadrajet. In not being a wiseass, Im just looking o be schooled on q-jets.

Also- is 750 a good size for a mildly worked 454? All the online calculators say 650 is ample, but Im running a 670 on my modified 350 and its a great combo.
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Old 04-26-2012, 04:40 PM   #12
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Not sure if Lars is still doing carb work, but good contacting him v8fastcars@msn.com, for his Q-Jet papers. You'll quickly see why he doesn't much like commercially rebuilt jobs. I personally like Q-Jets, but usually go with unmolested factory jobs, and set them up the way I like from there. Main advantage of spread bore designs, is running on the small front two barrels around town, for fuel milage and low rpm throttle response.
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Old 04-26-2012, 05:56 PM   #13
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Not sure if Lars is still doing carb work, but good contacting him v8fastcars@msn.com, for his Q-Jet papers. You'll quickly see why he doesn't much like commercially rebuilt jobs. I personally like Q-Jets, but usually go with unmolested factory jobs, and set them up the way I like from there. Main advantage of spread bore designs, is running on the small front two barrels around town, for fuel milage and low rpm throttle response.
Ill shoot him an email. Thanks. I shudder to think what a unmolested Quad will cost. Where would I even start looking for one? Stay away from remans? Even through a well known company like SUmit?
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Old 04-26-2012, 06:03 PM   #14
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Quote:
Originally Posted by Scottd View Post
Why is that? Ill have the money to spend, I just dont want to spend it if its unnecessary. I detest Edelbrock 1400 series carbs because of the horrible heat sink/vapor lock problems Ive had with them. I also hate running adapter plates to counter heat problems and carb/intake pattern differences. If Ill ultimately be happier with a square bore carb and intake, Im all ears to hear why Ill be disappointed with a quadrajet. In not being a wiseass, Im just looking o be schooled on q-jets.

Also- is 750 a good size for a mildly worked 454? All the online calculators say 650 is ample, but Im running a 670 on my modified 350 and its a great combo.
You stated in your previous post " Stuck with a spreadbore" and dont want to change the intake! By all means go with the Quad if you can find a good one.
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Old 04-26-2012, 06:19 PM   #15
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You stated in your previous post " Stuck with a spreadbore" and dont want to change the intake! By all means go with the Quad if you can find a good one.
Gotchya. I mean for now, I think it would make more sense to put the proper carb on the intake and work on tuning the overall car before I really dig into performance issues. From what I know, its a mild 454 (aftermarket cam, headers and intake), so is a Quadrajet 750 too big for the engine?
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Old 04-26-2012, 06:25 PM   #16
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Actually, just sunk in your mention of a Brock carb and intake, really meaning Edelbrock. Edelbrock carbs were Q-Jets through the mid 90's, so means you probably already have an unmolested one. Believe Edelbrock still sells Q-Jet meter rods/jets and such, so maybe contact their tech line, and see if they'll help you set it up better for your current combination. If getting to much heat from the intake, maybe try partially or fully blocking off the exhaust heat passage. You'll need to remove the intake for this one though. Also, good idea running an enclosed air cleaner housing, hosing in fresh air before the radiator, rather than an open element using hot underhood air.
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Old 04-26-2012, 06:36 PM   #17
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An Edelbrock 1407 is a square bore carb.
Edelbrock spread bore manifolds usually (maybe always) accept square and spread bore carbs. (But not 4-Jet configurations.)

Edelbrock Q-Jets are numbered 1901, 1902, 1904, 1906 and 1910, I believe.
They are great carbs; the one to get is the 1910 RPM model, but all are great starting points.

"Edelbrock 1407 Performer Series; Carb; 750cfm; Sq Flange Man. Choke;w/o EGR;Incl. Pri. Jet-.113;Sec. Jet-.107;Metering Rd-.071x.047;Dual/Small Single Plane Intake; Street/Hi Perf."

Last edited by Jeff_Keryk; 04-26-2012 at 06:42 PM.
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Old 04-26-2012, 06:39 PM   #18
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Have you considered a Holley spreadbore carb like this?

http://www.summitracing.com/parts/HL...555C/?rtype=10


Keep the shiny side up!
Scott
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Old 04-26-2012, 07:58 PM   #19
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FWIW: Here's a link to a thread regarding Quadrajets vs Holleys. Lars provides a lot of comparative info.

http://forums.corvetteforum.com/c3-t...-question.html

BTW: I have a QJet on my 454, mild cam. Works fine.

It shouldn't be that hard to find an unmolested QJet though it will probably need to be rebuilt.

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