MSD 6BTM...How does it work?

[Guest DaneL24]

I've heard all about this system, measures boost PSI and retards timing accordingly, but haven't heard how it works. I read that it can work with a regular distributor, so does it have a mechanism that retards timing on a distributor by shifting position of the breaker plate? Or does it somehow work electronically and uses a sensor to detect the boost. It just doesn't make sense how this system retards the timing on a distributor. Someone please explain what hardware it uses and how it works.

 

Debating between using high compression L28 or L28ET for a 240Z I recently bought. If I go with the L28ET, I will be interested in using this system.

[Mudge]

Modern day OEM retard, works by dropping (no spark) spark to a cylinder or two at a time for 50-100 RPM approximately to kill power. Some dont like this for a boosted app, so maybe it works differently?

 

Since it would use the dizzy (?), then it could detect what position the crank is at and just retard timing by actually retarding it, instead of taking it away. This would be like a crank position sensor or cam position sensor, which the ZXT cars and probably ZX cars have.

 

It would have to have a MAP sensor to detect boost, unless it uses RPM to determine when to drop spark.

[speeder]

The MSD Boost Retard boxes incorporate a manifold pressure sensor that works to delay the ignition trigger in proportion to boost, effectively retarding the spark. They work with standard electronic distributors as found on the ZX -both turbo and NA types.

I used one of these for years and it is effective in tuning a turbo car.

Mudge, you are thinking about rev limiters dropping spark to prevent RPMs going over a set point, the BTM doesn't work like that.