1972 280SEL v8 D-jet w/ CB black box Timing setup

[auriga]

I have a all stock 72 4.5V8 with original D-jet. Recently came across a thing called CB black box. Bascially its an additional device hook between the distributor output and coil, that can control the timing base on rpm and vacuum.

I think the original spec for those engine are at 5 degree btdc(no vac), and about 25 at full advance. WIth this box the timing can go up to 45 degree.

Im just wondering, whats the maxmium timing those engine can take before a knock? I assume this degree will be a lot higher than modern car because its such a low compression engine. But Im having a bit detonation at 3000rpm with timing at 38 degree. I need to verify the timing at 3000rpm is really at 38degree, because my distributor was locked down by zip tie not something more stronger.

Anyone have a suggestion on the timing map?

[Frank Reiner]

The CB folks have been doing VW Bug tuning for quite a while. The processes involved in creating ignition delay curves are in use thruout the realm of automotive tuning. The usability of any aftermarket product is dependent on quality and after-sale support. If this product works as well as advertised, then it is of use in the OPs situation.

In general, the M117 of the Djet era will tolerate 33-35 degrees before at WOT above ~3500. Light throttle cruise can be up to 45-48 deg. with low MAP.