My 66 uses an MSD Ready to Run distributor (no box). I run a stock small cap to keep it looking original. My coil started to leak oil so I bought a new black MSD Blaster 2 coil. Once installed my vintage Sun SST 802 R tach would read way too high at idle. I switched it to a stock type coil and the tach works perfect again. I will say spark is greatly improved with the MSD coil. Seems to start a bit better. Not sure if it runs any different. The primary resistance is much lower on the MSD coil, .6 vs 1.8 ohms. Anyone every encountered this and know if a fix for the tach issue?
Thanks in advance
Rob
cdnpont said
Oct 8, 2022
I'll bet a 1 ohm resistor in line with the tach signal input would fix it. Is there not a "Tach adapter" for just this problem?
horder said
Oct 8, 2022
I dont think 1 ohm in series with the tach will help. Im thinking the lower resistance of the MsD coil causes less voltage drop across the coil. So, the tach gets a higher voltage wave at the same frequency. Possibly something that matches the input resistance of the tach to create a voltage divider. Ive heard 10k ohm, I tried it with no luck. Same problem.
Maybe i should try a potentiometer. I could increase or decrease it to find a correct ohmic value?
Ill try a 1 ohm and post the result. 1 ohm wont have any drop across it in series with the tach, but Ill check it out.
horder said
Oct 8, 2022
I just measured the input resistance of the tach. Its 250k ohms so its no wonder the 10k ohm resistor did nothing to make it better. Ill try a 50k and a 100k ohm on Tuesday.
horder said
May 28, 2023
I put the MSD coil back in and started playing with resistors in series with the Sun Tach. Ended up that a 33k ohm resistor did the trick. Just thought id close the door on this one in case someone else has the same issue
My 66 uses an MSD Ready to Run distributor (no box). I run a stock small cap to keep it looking original. My coil started to leak oil so I bought a new black MSD Blaster 2 coil. Once installed my vintage Sun SST 802 R tach would read way too high at idle. I switched it to a stock type coil and the tach works perfect again. I will say spark is greatly improved with the MSD coil. Seems to start a bit better. Not sure if it runs any different. The primary resistance is much lower on the MSD coil, .6 vs 1.8 ohms. Anyone every encountered this and know if a fix for the tach issue?
Thanks in advance
Rob
I'll bet a 1 ohm resistor in line with the tach signal input would fix it. Is there not a "Tach adapter" for just this problem?
Maybe i should try a potentiometer. I could increase or decrease it to find a correct ohmic value?
Ill try a 1 ohm and post the result. 1 ohm wont have any drop across it in series with the tach, but Ill check it out.