Carburetors - Spreadbore and Squarebore

What are spreadbore and squarebore carburetors?

In cruising and driving cars, a spreadbore carb will provide better fuel economy and driveability due to its smaller primary openings, while providing the large CFM needed for max power when the large secondaries open up.

A spreadbore carburetor (think Quadrajet) has smaller primary barrels and larger secondary barrels.

A squarebore carburetor (think Holley) is a 4 barrel carburetor with each barrel having the same diameter.

Quadrajet Models

4M = early manual choke
4MC = hot air choke on early carb
4MV = early divorced choke
4ME = electric choke on early carb
M4MC = modified (1975+) Qjet w/hot air choke
M4ME = modified (1975+) Qjet w/electric choke
M4MEA = modified (1975+) Qjet w/electric choke & Altitude calibration
E4MC = 1980s electronic Q-jet w/hot air choke
E4ME = 1980s electronic Q-jet w/electric choke

Oldsmoblie 442, H/O Quadrajet #s 307ci VIN"9"

1989,90 - (Cadillac Brougham) 17086009
1988 - (Cadillac Fleetwood H/O) 17086009
1986,87 - 17086009
1985 - 17085554
1984 - 17084554

Monte Carlo SS Quadrajet #s L69 305 H.O. VIN "G" and "7" (1983 only)

1987,88 - 17087129
1986 - 17086003
1985 - 17085202
1984 - 17084208
1983 - 17083206