The tach on my car doesn't read right.
 

I just got my 6.0 71 Vette running and the tach doesn't work right. I had the stock mechanical tach converted to electronic internals from a 75 last year and it worked fine with the MSD box on my SBC. With the 6.0, it works a little but is very lazy and doesn't ever read above 2000 rpm, even when I'm sure it's at 5000 plus.

I have it hooked up correctly.

I tried the resistor pull up wire and that did not make a difference. I tried 4700 ohm and 470, neither worked.

Someone has to have seen this before.

Any ideas?

You know the LS1 has a 4 cylinder tach output right? That's probably your problem since your tach was setup for an SBC which has a traditional 8 cylinder output.

try gettin a computer or pcm swap r even a programmer might fix it

I started to think that way after reading a few threads. My tach is probably just reading at half speed. I'll have to have wait4me fix that. My tune will probably need a couple touchups anyway.

I think you are on the right track