Square-bore vs. spread-bore?
Maybe I missed it but I haven't heard anyone explain why they made the "spread bore" type carb. Probably 90% of the newer generation won't know because their cars have all been fuel injected since the late eighties.
"EMISSIONS" " FUEL ECONOMY" The small primary/large secondary carb gave good low end economy because of the lower cfm flow when only the primaries were open. Generally low speeds and light cruising but had a huge boost when the secondaries opened when passing another car etc... The Thermo -quad was Crates most advanced carburator of the time. The Carter design with the float bowls being one piece allowing the top of the carb to be taken off for service without draining or spilling fuel on the engine, like the Holley. The Phenolic main body was an insulator keeping the fuel many degrees cooler that a standard carb. This allowed denser fuel charges and resistance to vapor lock in hot conditions. The vacuum secondary system ( AVS) allowed for the smooth transition from the primaries to the secondaries with out bogging when tuned properly.
Thermo-quads became the performance carb for Chrysler. Look at the performance engines and cfm rating of those carbs. in the seventies.
Holley dominated the aftermarket in carb sales and that is what drives the manufacturers of manifolds when they design them.. $ale$
