Were there different types of Tach outputs ever used in the F bodies 3rd generation cars? I have just installed a new 350 in an 86 and hooked up the factory tach to the standard tach location. Reads high, almost as if the tach is set for a six cylinder. Had 305 with TPI in it originally and its the iroc z model. I am using the HEI that I had in the old vette motor all along. Figured it would simply work and know it has better insides than the one that came out. Runs like it always did but tach is reading wrong. Were there different distributor modules or tach filters used? If I still had the 86 distributor I would change it back for the heck of it, but its gone.

Seem I read something somewhere that led me to believe there was a different distributor called for in 86 and after than in 85 and before. Saw a dividing line somewhere in a catalog, but cant remember where?

May simply be a bad tach anyway.

Need the OE dist for the OE engine, you might try a reman from the aftermarket.