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I'm not sure about the technicalities, but the theory about the tach is that it reads when a spark fires on a certain cylinder and then from that calculates the RPMs. So when you go from a 4 cylinder to an 8 cylinder the RPMs I think double (on the tach). So short answer it won't work correctly. I'm sure someone here knows the correct reason, but I don't remember.

Milan
 

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I hooked my factory SR5 gauge to my chevy 4.3. Before I fixed it it would rev very abrutly. Excuse my sloppy ass spelling but what you need is a potenshiaometer. I have no idea how to spell it but that is what it sound like. You take your cluster out and wire this little thing to the back of your tach. You then set it to either 4cyl or 8cyl.

I think I bought mine at Radio shack. My engineer friend told me about it.

It made my factory tach work perfectly.

Rick
 

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<font color="yellow">
{Cue 'Mighty Mouse' music}
Here I come to save the day...

It's called a POTENTIOMETER and you can read all about what the heck you do with it.

BTW: A potentiometer is nothing but a variable resistor. It's the same thing that's behind the volume knob on a radio. It won't come with instructions because it's just an elecctrical component that can go into any of a million different things.</font>
 

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I am also trying to do this mod. I got the potentiometer, but have not figured out exactly how to hook it up. That web site doesnt show the installation at all. Can anyone explain the installation to me?

There are 3 connectors on the potentiometer. Which ones do I use? and where do they get hooked up to the cluster.

Thanks.
 

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Last five years I've got use to looking at the RPM and dividing by 2 in my head. Five years ago I got a hold of Jays tech page and tried to apply it to the '83 tach. Did not work, but I could have not had it right. I still have the stuff to try again but have not bothered. If somebody finds a easy way to convert the stock '82 '83 tach. I'm all ears. <IMG SRC="smilies/usa.gif" border="0">
 

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I've done this to my 86 w/ a 4.3. Works great. I'll try to explain, but please don't take this as gospel.

I bought a small two-post adjustable potentionometer (sp?) from a local electronics supply center. I soldered 2" of wire to each terminal on the potentionometer to give me more flexibility.

Took the tach all the way out of the instrument cluster and removed the plastic piece on the back of the tack to gain access to the terminals on teh back of the tachometer. These are NOT the terminals/connectors to the instrument cluster, but rather two terminals, one on each side, inside the tach itself.

I soldered the wires to the terminals and used a tad of contact cement to mount the potentionometer to a "slightly" accessable place on the tach.

I then attached an aftermarket Tach to the engine to give me something to tune the factory tach to. I started the engine and adjusted the potentionometer (with the engine off - I had to pull the cluster to get to the potentionometer) until it read the same as the other Tach (i think I'm a tad off, but close enough). The Potentionometer is very sensitive and it takes a long time to get things adjusted properly, but it's well worth it.

Jay can explain it much better than I can.

bkg
 

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I am still not sure which way to connect the potentiometer. Does it hook from the signal wire over to the ground witht eh factory connections still in tact?
 
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