Q: Changing to a 4 Barrel Carb for a 1968
When changing from a stock 2 barrel setup, to a 4 barrel, what parts are need to be changed, and what donor years are ok. The car is a 1968 350 automatic, and I have a freshly rebuilt Q jet.
A: It’s not a difficult swap, but there are a few gotchyas to look out for.
-Spreadbore intake castings are pretty much the same from 1968 thru 1972. In 1973, Pontiac started using an EGR valve, and in 1976 or 1977, the intake was redesigned with more restritive ports. Thes are identified with an odd waffle imprint on the rear of the intake, behind the carb flange. These characteristics make these later intakes less desireable. Some 4bbl. intakes before 1968 were for squarebore carbs (using Carter AFB carbs), and the 1967 Qjet intake has an odd heat passage on the carb flange.
-Throttle cables and cable brackets differ from 2 bbl. and 4 bbl. applications. You will find that your 2 bbl. cable will not give you a full range of motion and may require some fabrication to get full throttle. Reproduction 4 bbl. cables are now available from Performance Years. You’ll have to hunt the scrap yards for the bracket, or modify yours. (Need link to modify instructions)
-More on throttle brackets. Pontiac used a rod for 1967 cars, and then went to a cable for the 1968 and later cars. This cable is very different from that used in later Chevy applications. Around 1970 or 1971, the cable and bracket design changed again, eventually evolving to be more like the Chevy design. So, beware of cables or brackets from earlier or later cars (you don’t indicate what year your car is).
-You’ll need a 4bbl. aircleaner. If you insist on a stock look, try First Generation Firebird’s, ebay’s, Classical Pontiac’s classified pages.
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Content last modified: January 15, 2014 at 1:10 pm