Not really sure where to go with this.
I have a firebird with a TBI 305. 120 mph speedo and 6000 tach. I put in an 8000 tach out of a V6 and found the only difference is the face. It still positions the needle as if it was a 6000 tach. What do I need to change to get it to read for an 8000 tach? Also have a 140 mph speedo, will I need to do something to make that read right too?

 

Let me be the first to welcome you to the boards. Another fellow TBI owner, I see.
I'm pretty sure that the tach for the V6 is different than the V8 one. That gauge is calibrated differently between the two engines. You'll probably want to get one from a V8 car. There may be a way to change the way the gauge reads, but I wouldn't bother messing with it.
The speedo should work, give it a try.

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DR Stevens
1984 Trans Am 305HO L69
1991 Firebird 305 L03

 

Thanks for the comment. You are absolutely right about getting the right one to start with. From what I can tell, I think it is safe for me to say that a V6 8000 tach is a V8 6000 tach. The only difference is the way the numbers are positioned on the face to make it read correctly for the number of pulses it is receiving. The problem is not that they are different. The problem is that they are the same and I can't swap anything from one to the other. If there is a way I can stop it from receiving every 4th pulse from the engine I could then maybe make the V6 tach work. Somehow make it unable to read cylinders 4 and 8 in the firing order.