Some people trim their weights, change their springs to change the timing characteristics. I've got a distributor from Tom Langdon, think it's from the Atlas-6 engine, so was curious how my timing came out. I'd like to compare it to others. Engine L250 with flat-top pistons and a medium CAM. I've got a really nice Bosch timing light with digital readout for advance and RPMs and used grease pencil to make the "0" marking really clear.
First thing that really surprised me was that the timing advance dropped from 700 RPM to 1000 RPM. With vacuum on, the idle works well at 970-1000 RPM. Goes down a bit when the fan goes on, relay is on the same circuit.
Mechanical advance kicks in at 1650 RPM.
Vacuum off. % is (adv change)/(rpm change)
6.3 @ 720
5.5 @ 1000, -0.8, -0.29%
8.1 @ 1800, +2.6, +0.33%
11.0 @ 2000, +2.9, +1.45%
12.6 @ 2500, +1.6, +0.32%
15.0 @ 3000, +2.4, +0.48%
Vacuum on.
30.5 @ 970. 24.5 timing & 250 RPM increase by adding vacuum
30.5 @ 1600
32.6 @ 1800, +2.1, +1.05%
34.6 @ 2000, +2.0, +1.00%
37.2 @ 2500, +2.6, +0.52%
39.2 @ 3000, +2.0, +0.40%
I was afraid the neighbors would call me in if I did higher RPM. :-)
