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Old 03-11-2026, 01:11 PM   #1
yote1234
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Location: Gold Canyon Arizona
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need help. switching a holley to quadrajet carb

i bought a gm new crate sp350/357 engine. it came with a 670 holley carb and i want to install a fresh rebuilt quadrajet 4 bbl carb off a 76-79 454. that i have sitting on my shelf. i was looking for a more simple install. and wanted more reliability. I also want to keep it all GM. All this is going into my fresh 1971 k5 blazer i am restoring.

Now for my question.....
Can anyone tell me the adapter plate i need to buy? the gm crate engine came with a gm intake to fit the holley carb. and again wanting to install my 1976 ish quadrajet carb. I Thank you,
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1965 C10 Short bed all original
1949 gmc 100
1968 Honda mini-trail z50a #377
1966 uh 1-D Huey
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Old 03-14-2026, 04:05 AM   #2
Richard
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Re: need help. switching a holley to quadrajet carb

A standard square bore to spread bore adapter should work. There are two types. Fully open or tapered holes.
Open type https://www.amazon.com/Carburetor-Ad...3474121&sr=8-6
Tapered holes https://www.amazon.com/KIPA-Carburet...zcF9tdGY&psc=1
Been a long time since I have used one. I cannot recall if direction matters. Meaning spread bore carb to square bore manifold only or the opposite. Hopefully someone can chime in if they work both ways. One description says it can just be flipped over as I recall.
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Last edited by Richard; 03-14-2026 at 04:55 AM. Reason: fix link
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Old 03-16-2026, 05:45 PM   #3
yote1234
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Re: need help. switching a holley to quadrajet carb

awesome Richard. got it ordered
thx,dave
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1949 gmc 100
1968 Honda mini-trail z50a #377
1966 uh 1-D Huey
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