Quadrajet Problem Solving > Quadrajet Parts and Numbers

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Cliff Ruggles:
The single booster ring models are excellent, but every tightening emission standards in that time period simply would not allow them to be used past 1971.  As you mentioned lacking the outer rings hurt efficiency right off idle/low throttle angles and that's where the EPA wanted them to be the cleanest. 

They are excellent units and with a very slight recalibration work flawlessly on the big 455 ho engines.  They have several advantages over the standard castings.  One is that they flow 828cfm instead of 750.  They also delivery considerably more cfm on the primary side you can achieve more power and speed w/o the secondaries.

I've drag strip tested the 71 ho carburetors and they will outrun the 750 castings without much trouble and that's probably why NHRA banned them in stock and super stock classes unless you have a vehicle/engine combo that originally used one.

In 1973 Pontiac answered the problem with the 455 Super Duty carburetors which were the larger castings typically dubbed "800" cfm.  They actually flow closer to 850 same as the "famous" Edelbrock 1910 units, but they are much better carburetors than the 1910's, at least in stock form....imho.....Cliff

unruhjonny:
Thanks for chiming in Cliff!

my comments were not in any meant to diminish the performance or potential of the '71 single booster ring Pontiac Quadrajets, but was meant only to try to point out that the '71 dual booster ring quadrajets are (undeservedly) often overlooked - and good candidates as replacements for a 1971 Pontiac which has a wrong year/application carb to begin with.

I do believe that the advertised net horsepower ratings of the 1971 455HO matched the 1972 455HO - in spite of the different carburetors;
I am pretty certain the same can be said for 1971 vs 1972 400 net horsepower ratings.

Cliff Ruggles:
The 455 HO engines didn't have big enough cams in them to fully see the potential of the head flow, so there wouldn't really be any advantage to have a 1971 single booster carb on one vs the standard unit.

I've actually dyno tested those carburetors back to back on 455's at the 500hp mark, and they make equal power to about 4500rpms.  From there on up the larger carb will make more power. 

In terms of vehicle performance the difference isn't much because the engine will spend very little time above 4500rpms on a full throttle run. 

In terms of smoothness of idle, engine efficiency and MPG's, the standard version is going to win in all those categories. 

Couldn't comment on folks overlooking early Pontiac units, we like all of them here, and they are not getting any easier to obtain.  There still seems to be plenty of later units, 73-74's are in good supply, and there is little demand for them unless it's a Super Duty model.......Cliff

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