I think I read somewhere on here that the tach needs to be changed. This is fine as I have one, but my v-6 tach reds at 6000 which is close to my v-8s red. And the tach reads up to 8000. My v-8 tach reads to 6000, and reds at 4500 or 5000. Do i have to switch them? My v-6 tach works with the v-8, that's why I'm asking, basically I don't know if its acurate.

 

You'll need to swap them.

 

The V6 tach would read 25% too high (fast) if used on a V8 engine. However, the V6 tach face plate is much nicer because of the higher red line corresponding to what you will probably want with the new engine. So what I did was recalibrate my V6 tach for a V8 engine. There is a resistor on the back side of the tachometer that is used to calibrate the tach from the factory. You can swap out that resistor to set your tach up for a V8. I had a friend with a pulse wave generator and we kept adjusting the resistor until the tach was calibrated for a V8. We fine tuned it from 400 rpm to 8000 rpm.

 

can a new resistor be soldered in? I am in teh middle of my swap also and would like to keep the look of my v6 tach.

Any info about just changing it for the correct one? What would i need?

 

Sure can, im just not sure where the resistor chip is.

 

would you have to solder it or does it just snap in? Does anyone know where the chip is or how hard it is to swap?

 

Believe you solder it. Could be wrong, I just took the tack off my v6 and threw it on the v8 cluster.

 

The resistor would have to be clipped out and a new one soldered in place. Every resistor is unique to the tach for final calibration. There is no one part that will fix it. The other thing is that I really don't remember what the back of the tach looked like so I can't provide any more help than the idea itself. I can see right now that I should figure it out again and contract out my services!

 

pasky, is your tach acurate? I was thinking of doing this, and it'd be the easy way. the v-8 cluster reads to 120, and the six only reads to 85. I may just have to use the v-8 cluster.

Basically I either have to swap speedos, or swap tachs. BUT I can't just stick the 120 speedo in the v-6 cluster cause it won't be acurate. SO If I can just stick the v-6 tach in the v-8 cluster that would be awesome.

 

Not sure really, never looked at it when running datamaster, really don't care right now because its not moving, im pretty sure it would be if not i'll just adjust it accordingly. Helps when you have datamaster.

 

With the cable speedo setup. you can swap any cluster into any car as far as the accuracy is concerned; the actual sweep of the pointer is the same on all of them, for a given RPM range. Like, from 0 to 60 is 45° or whatever, no matter what the full range is.

On the tach, think about how a tach works for a minute. It gets pulses from the distributor. In a 6-cyl, there are 3 pulses per crank rev, but in a V8, there are 4 per; so for example a 6-cyl tach will read 2000 RPM when it gets 6000 pulses per minute. However, a V8 produces 8000 pulses per minute at 2000 RPM; so the 6-cyl tach will read 33% high, or 2666 RPM, if you hook it up to a V8 at 2000 RPM.

There is a resistor you can change; it's a little laser-trimmed deal on the ckt board on the back of the tach. It's the same one that changes value over time and makes all these tachs so inaccurate. I believe it's this one, although I've never dinked around with changing one.

 

I'll probably just use the v-8 cluster, and the speedo is electric.

 

if you need a v8 cluster with a cable spedo i have one