Anyone using a Sun Super Tach SST-802 with a DUI distributor package? Have my tach on my 72 442 350 with points/rotor ignition and the DUI guys say it will work with their package. Since this tach was designed back in the 60's for standard ignition I am a little hesitant about their answer. Anyone using one or is there a tach adapter available for these to be used for this type of application? I see MSD makes a few adapters but don't know if they are specific to their ignition systems.
Thanks,
Dan

 

"Should just work". It won't hurt the tach. Worst case it won't have a stable reading.
DUI are just tailored HEI units, and HEI modules generate a nice tach signal. Basically a cleaner version of what points would use to trigger the coil (and thus what old tachs are looking for). Sometimes that cleaner version is more susceptible to noise interference, hence why some guys use filters right before the tach. But, plug it in and try! Just use the tach output off the distributor.
Adapters are usually only needed when going into a multi-coil ignition system where there's not a single signal that clicks along with engine RPM. Or if you're using a capacitive discharge ignition (don't want to use the coil leads on those!!) that for whatever reason doesn't have a tach output.

 

A tach just reads the frequency of the on/off cycle in the coil primary side. The TACH output on an HEI mimics the signal you would see if you connected to the "-" terminal of the coil on a points-type ignition system. The problem comes with multi-spark systems like MSD, which confuse the tach.

 

Yes. Multi-spark systems would do a good job confusing any tach. MSD controllers avoid this by providing a dedicated tach terminal that outputs a square wave that the tach can read without confusion.