I have a sbc 350 with a 2 barrel carb.Engine has upgrades. I know the 2 barrel is a bottle neck for performance.I have had to go to test only with this car.My ? is if I swap to a 4 barrel intake/carb would this be a prob when time to smog test.Speaking on the visual and sniffer.Due to the car did not come with a 4 barrel carb.Been told when test only you better have on the engine how it came from factory.I even had to go to a single flowmaster due to the car did not come with dual exhaust from the factory.Another ? will the 4 barrel burn more fuel if your not stabbing the peddle?  

Typically the sniff test is done at idle, the four barrel can run just as clean at idle if set up properly. You need to check with the inspectors to see if modifications are allowed in your area.  

Here in Calif smog test is done on a machine similar to a dyno.Test is ran at low speeds 15 to 25 mphs then up to if I remember correctly 35 mph.Takes about 3 mins to complete the test.Going to go to inspector and ask some ?'s.Thanks for your input.  

Unless the inspector starts decoding your cowl/body tag and VIN number, how's he gonna know your car didn't come with a 4 bbl carb. If you went to a QJet carb and good manifold, that's basically what a version of your motor came with form the factory, and as long as it was an option in your car, you should be ok.  

Vin # is data added to smog test computer before the test begins.The computer starts the decoding from the start.I have done a little research.My car is a 77.Some came from factory with 4 barrel on the 305's and some came with 2 barrel and 4 barrel on the 350's.Its a certain letter in the vin # that states if it came with either 2 or 4 barrel on the 350's.Going to inspector and see if I have the letter in my vin for the 4 barrel.Thanks for your input.