Your vette distributor is sluggish to the tune of 1 degree at the distributor, 2 degrees at the motor. Using your numbers, you get a max advance (initial plus mechanical) of 34 with an initial of 12. That means your mechanical is 22 at the motor, 11 at the distributor. All chevy distributors that I have worked on, none were specificed at less then 12 degrees mechanical. So if the distrubutor was working correctly, at 12 degrees mechanical at the distributor, the vette distributor would be 24 at the motor, 36 total with the 12 initial (24 + 12). If you wanted to get to 38 total, you would bump your initial to 14 degrees (24 + 14). Fairly common timing for a gen 1 small block chevy.
On the rebuilt, that distributor is also likely within specification and not mal functioning. Chevy distributors generally come in 12 distributor degree advance versions and 14 distributor degree advance versions. Yours apparantly is the 14 degree variation. So instead of 24 degrees mechanical at the motor on a 12 degree distributor, yours is 28 degrees at the motor on a 14 degree mechanical. Add the 12 initial, you get 40 (28+12). So If you wanted to get 38 total on that distributor, you would time the motor for 10 degrees initial instead of 12 (28 + 10).
Now that you have installed the vette unit that is a little tiny bit lazy, you should also check your dwell specification and see if its within tolerance, and confirm its not jumping around. If it is, the lobes are worn unevenly.
Last edited by Dragsix; Wed Sep 21 2022 04:20 PM.