Joined: Fri Mar 13 2009, 11:21AM
Location: San Marcos, CA
Posts: 713
All AVSs are square bore, the only Carter 4bbl that is spread bore is the ThermoQuad (black plastic body). The separation of the primaries along the pivot shaft is very far apart (spread bore). The Rochester Quadrajet is another spread bore carb. They use the inner stud pattern on an aftermarket intake and the secondaries bulge out. My $.02
Joined: Sat Mar 29 2008, 03:36PM
Location: North eastern Wis.
Posts: 1638
66_monaco_500 wrote ...
The separation of the primaries along the pivot shaft is very far apart (spread bore).
This makes sense. I was under the impression the difference is in the bore size. The rear bores are bigger, thus wider pattern then the primaries. Outside dimensions are spread apart. Not Square. That also makes sense to me.
Joined: Fri Mar 13 2009, 11:21AM
Location: San Marcos, CA
Posts: 713
The '66 and earlier AFBs use the inner bolt pattern the same as the TQ and Qjet, but are square bores. The newer AFB/AVS use the same bolt pattern as a Holley. In addition, i should say that the Holley type 4165 and 4175 are spread bore too.
Joined: Sat Mar 29 2008, 03:36PM
Location: North eastern Wis.
Posts: 1638
can't remember where I heard it but same size bore just made sense over different size bores. Guess making sense to me is irrelevant. Anyway after all these years I can now tell the difference. We live we learn. 57 plus years old does not change that fact. Thanx everyone for setting me straight.
Joined: Fri Mar 13 2009, 11:21AM
Location: San Marcos, CA
Posts: 713
A square bore carb can have different size bores, many carbs have larger secondaries, but are "square bores" My '66 has a '69 375 horsepower 440 AVS and the secondaries are larger, but it is not a "spread bore"
Joined: Wed May 21 2008, 02:52PM
Location: Machine Shop Hell, IL
Posts: 142
Don’t be afraid to invest in a jet / metering rod / spring kit. Whatever is in either of those carbs, I almost guarantee you can do better with a scientific approach (and a wideband, heheheh).