you're going to have to readjust your tach or get a v8 tach. Your tach looks for the signal from the coil every time it fires. A v8 coil fires 2 more times per revolution of the crank than a 6cyl does.

 

A lot of tachometers have a series of dip switches that are positioned in a certain order for engine type. Would start there

 

Your V8 doesn't have a multiple spark ignition, does it?

 

And yes I did change the tach setting to work with an 8 cylinder beforehand.

maybe that setting is not working correctly? has it been used on a V8 before, or only the 6C?

do you have a fancy wasted spark ignition on the V8? those fire every cylinder every revolution.

 

The Tach is set to the V8 setting, no I do not have a fancy ignition system...just a mallory unilite dizzy with an msd blaster coil. It has only been used on a 6 cylinder car before.

I read that I might need a voltometer to get a reading from the ground and hot wire see if they are at 12v. Now to buy one.