# Carbs.



## Nicholas (Jan 16, 2017)

Hi everyone. Just wondering, is there much difference between a '71 carb. and lets say a '70 carb. They look similar and I think will bolt onto the same intake. I was actually thinking about the performance between the two. In '71 Pontiac decreased the CR and I'm not sure if that affected the carb. also. Thanks for any replies, Nicholas.


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## bigD (Jul 21, 2016)

Nicholas said:


> Hi everyone. Just wondering, is there much difference between a '71 carb. and lets say a '70 carb. They look similar and I think will bolt onto the same intake. I was actually thinking about the performance between the two. In '71 Pontiac decreased the CR and I'm not sure if that affected the carb. also. Thanks for any replies, Nicholas.


I'd prefer a non-California '70 model. They were for higher compression engines and did not have those big "smokestack" vent tubes, which require a hole in the air cleaner base. All '70 Calif & '71-'78 Pontiac Q-jets had the big vent, as far as I know.

If you are looking for more performance, you may wanna consider a Buick 800cfm, from the early '70's. They came on lots of 455 engines. They have the front inlet, like a Pontiac, but the throttle lever is a little different, & the return spring location is different. And, they do not have the big vent. 

http://www.everyday-performance.com/quadrajet_carburetors.htm

After '75, most Q-jets were 800cfm, but require more internal mods for performance use.

Cliff Ruggles says that one of these later 800's is the best core for building a performance Q-jet. One reason is the APT feature, which the early models did not have. They also have the hot air choke, which began in '73, which can be very easily changed to an elec choke. The 403 Olds engines came with one of these type, which did not have the big Pontiac style vent.

http://www.smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100/productID/841


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## shader (Sep 7, 2016)

Nicholas,
Some good info there from bigD. Briefly, the quadrajets between years share the same throttle body bolt pattern & will bolt up. The main difference between years, and also within the same year is the metering circuit (jet and venturi size, metering rods) and the transmission type as the carbs are setup from the factory for specific applications. The link shows Pontiac 4-bbl carbs and their apps. 


Pontiac 4 barrel carburetors part numbers


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## Nicholas (Jan 16, 2017)

Yes, some good info there. I already looked at those 2 linked sites. Impressive. Thank you very much, Nicholas.


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