tach differences

[michael bustamante]

So im just starting to learn about our factory tachs. First question: how can you tell the difference between the 6 and 8 cyl. Tachs?
Second question. Can a six cyl tach be used on a 350 w hei?

[leddzepp]

6 or 8 cyl will be stamped on the back, as well as a part number. They are not physically different.

A 6 cylinder tach will work with your v8, but it will not read correctly.

[michael bustamante]

Ok great. Thank you

[michael bustamante]

Ok guys i just got my tach dash. 1967.
The marking is unreadable. Any other way of telling the difference? There seems to be some sort of adjuster screw on top in back

[michael bustamante]

Where are the part #s on the factory tachs? I could really use some help on this one

[michael bustamante]

anyone?

[ray_mcavoy]

The factory part numbers were originally ink stamped onto the back of the tach along with the markings for 6cyl or 8cyl.

GM #6468321 is for the 6cyl gas engine tach.
GM #6468228 is for the 8cyl gas engine tach (except medium duty trucks with transistor ignition).
GM #6468320 is for the 8cyl gas engine tach with transistor ignition.

I believe all of the diesel tachometers in this year range were cable driven so one of those should be easy to identify. Unfortunately, I don't think there is an easy way to ID the electronic tachs used with gas engines if the ink stamped numbers on the back are no longer readable. I suppose you could hook it up to your engine along with a known tach and compare the readings.