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Discussion Starter · #1 ·
The PO replaced the original carb with a Holley. The old carb and the box for the new carb came with the car, and the box says Holley 600 cfm vacuum secondary, electric choke, square. Now I know (or at least have an idea) what all that means, except for the "square" part. What is that all about? Also, when you buy a new carb, does it come with replacement jets and all that jazz I'm always reading you guys talking about?

The PO also installed a new Edelbrock intake, if that matters. I have the box for it as well.

thx
 

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Square bore as opposed to spread bore. That is the mounting flange bolt pattern. I've never seen a new carb come with extra jets. I've always bought a jet kit from Holley.
 

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Discussion Starter · #3 ·
monkeystash said:
Square bore as opposed to spread bore. That is the mounting flange bolt pattern. I've never seen a new carb come with extra jets. I've always bought a jet kit from Holley.
Well now we're getting somewhere. Now the obvious question: what is the difference between the bore types, and is there anything special I should know about square bore?
 

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Square bore = all four primary and secondary holes are the same diameter

Spread bore usually means the secondary holes are larger.

The old Rochester carbs used on GTO's and early Firebirds had a spreadbore design. The front primaries were about the diameter of a half dollar coin... the rear primaries would almost swallow a tennis ball (minor exaggeration). When the secondaries opened up on those old GTO's, you'd better be holding onto something, tightly.

Dave
 

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DaveSanborn said:
When the secondaries opened up on those old GTO's, you'd better be holding onto something, tightly.

Dave
You got that right Dave! Of course I'm a bit biased too.

http://memimage.cardomain.net/member_images/4/web/2572000-2572999/2572060_1.jpg
 

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Sweet! Here Come Da Judge! Nice car! My second hot rod was an original '65 with the 389 4V, close ratio Muncie 4spd, 4.10 rear, factory Hurst shifter, center console, factory dash tach, wood grain stering wheel and a backseat that saw a lot of action ;)

I found it in a neighbors field and paid a whopping $125 for it (1977 dollars, with inflation and collectability calculated in, I guess that's the equivalant of about $50k in todays dollars). I drove the heck out of it for 2 years of HS and then sold it before leaving for boot camp. I made a nice profit, or so I thought... I sold it for $400.

Yeah, 30 years later and I'm still kicking myself...

Dave
 

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Spreadbore carbs were often Quadrajets as well, which were often called Quadrajunks. Unless you are using an OEM type intake, you will typically have a squarebore carb and intake. I don't recall too many aftermarket intakes made for spreadbore carbs.
 

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DaveSanborn said:
My second hot rod was an original '65 with the 389 4V, close ratio Muncie 4spd, 4.10 rear, factory Hurst shifter, center console, factory dash tach, wood grain stering wheel and a backseat that saw a lot of action ;)
Dave
I love '65s, probably my favorite GTO. Too bad you sold it, but who knew back then? Mine also has seen a lot of action, just not in the back seat. :(
 

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I don't recall too many aftermarket intakes made for spreadbore carbs.
Yep. Not many come to mind. The squarebore carb is the popular style carb. They do market an adapter though to mount a squarebore carb onto a spreadbore intake.

Dave
 

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On the jets, dont new carbs noramlly come jetted for sea level?
 

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How quickly we forget the 4300D which was a spreadbore carb used on the Mustang from 1971-73 (Boss 351s and Q-codes). Weird thing about this carb was that it had the square bore bolt pattern.
 

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DaveSanborn said:
Sweet! Here Come Da Judge! Nice car! My second hot rod was an original '65 with the 389 4V, close ratio Muncie 4spd, 4.10 rear, factory Hurst shifter, center console, factory dash tach, wood grain stering wheel and a backseat that saw a lot of action ;)

I found it in a neighbors field and paid a whopping $125 for it (1977 dollars, with inflation and collectability calculated in, I guess that's the equivalant of about $50k in todays dollars). I drove the heck out of it for 2 years of HS and then sold it before leaving for boot camp. I made a nice profit, or so I thought... I sold it for $400.

Yeah, 30 years later and I'm still kicking myself...

Dave
Yeah, a HS buddy of mine also bought a 65 goat. Bought it about '72 for $125. It was missing the engine which was a tri power 389 that the PO blew up. We stuck in a 400 2bbl from a 67 wagon. With it's low end torque and 4.56 gears, it was a holy terror to drive sanely on the street without frying the tires every time you let the clutch out.
 

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I say ditch the Holley and put a Edelbrock on. On www.fordmuscle.com they tested the Edelbrock intake and carb against a 2 Holley Avenger carbs and the new Wieand intake. The Edelbrock set the standard in both power and constant fuel mixture.
 
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