The 3810 was never used on a Z - it's a 585CFM model 4160 single-inlet with only a primary metering block, secondary metering plate only, and non-externally adjustable needles/seats; was used on '67 Corvette 327/300hp and 327/350hp engines. The 3910 is the 780CFM model 4150 dual-feed used on the '67 Z.