My experience passing CA smog 2021 with a 401 4 bbl disguised as a 360 2 bbl. Disguised with oil leaks and paint flaking off
the wagonner was originally from Cali with underhood sticker still intact.
I installed the Howell 401 efi kit with CARB E.O. The kit came with a gm tbi to 4 bbl adapter plate that installs ( poorly) on the cast iron 4 bbl intake manifold with egr. This kit allowed the airpump and most vacumm smog crap to be removed. Except the carcoal canister is retained!
The 401 has Doug Thorley headers which also have CARB E.O. number and HEI. I had to get a Pertronics cap and rotor, which also comes with CARB E.O. number (distributor did not). Lastly had to install a new California approved catalytic converter with air tube blocked and keep single exhaust. Did bump up to 3 inch.
Took to a STAR smog shop in San Diego and gave all the installation manuals. After looking them over, the tech agreed to tailpipe smog. I have manual hubs and 2 speed dyno run was done.
Everything was checked! The egr function, the gas take was pressure tested, the serial number on the catalytic verified, pvc unplugged and rattled, check engine light, and vacuum lines installed like underhood Howell sticker.
Verdict: passed well below 360 2 bbl max values in all categories, even with a 401.
Verdict on the Howell efi on a 401. It was a nightmare with zero ability to modify the ECM. First, Howell sent me a bad ECM that took 2 weeks of monkeying around to diagnose (bad internal tach filter). Looked for vacuum leak as everyone suggested. Adapter plate on 4 bbl intake sealed poorly due to not much lip for rtv and gasket. 3 installs to frankly seal, Id switch to 2 bbl intake. Howell says factory fuel line sizes are okay. But 1/4 metal return line forced excess fuel into the tbi and flooded the engine randomly. Moved up to 5/16 line did the trick on stalling but tunerpro still shows running rich. Temp sensor plug was making a poor connection and would flood the engine randomly too. Diagnosed after a second temp sensoring doing the same, fixed with crimping the plug prongs for a more secure connection.
The benifit of efi. Besides CA smog and starting easier. It still runs rough cold until closed loop operation at temp, no choke. Im down on power compared to the 4bbl. Mileage same, worse then horrible. The ecm only gave a code once with all the flooding problems.
Unforseen. I have electric fans on a temp switch in the intake. The only spot for a temp sensor, which is now need for the efi. I got creative and installed a brass T on the rear heater line port off the intake for a second sensor.
Maybe the Howell 360 efi kit with 2 bbl adapter and stock exhaust is a smoother install. Next time, cheap LS swap no question!!!!