Hello everyone!
New to the forum here, been reading great info from the site for a long time... Thought I would finally join... Plus I have a question

My apologies if this question has already been asked and answered, I looked but didn't find the answer on the forum.

I'm working on a 1991 RS, it has previously been carb and HEI swapped and now I'm working on it, attempting to make all the gauges work.
I have all the gauges working good in the factory cluster now, all except the Tachometer.

Should the factory tach work with the HEI?
The needle goes to about 3500 RPM with the engine idling, and move higher when you rev the engine. Are the 91 Tachs incompatible with HEI? or do I have a bad Tach?

Thanks again for all the great info on here!
Keep posting!

Smitty

 

I've never heard of them being incompatble, but I dont know for sure. It'd be nice to find out considereing I'm about to put a 383 with an HEI in my '91. DO you know anyone with an aftermarket gauge that you can quickly wire in to see if its the tach or the signal from the dizzy?

 

Hi Smitty ,

Was this car originally a six that has had an eight swapped in ?

Cause if so , that would be a great reason for your tach to read high . If you search around here a bit more , there was a thread someplace about a particular failure that can cause the tach to read high as well . If it was a 6 and is now an 8 , you'll need a tach out of an 8 cyl car . But if it was always an 8 , you may want to try to find that thread I saw about a home fix for a tach that reads too high .

Good Luck with it ...

 

They are compatible.

THINK... since late 1974, EVERY GM car that has had a tach, HAS ALSO come with HEI.

Sounds like your tach merely has the usual failure that virtually all of them do, whereby it reads high. No big surprise there. Certainly no need to invoke "HEI" to try to explain it.

 

So, before i got my car most of the stock engine wiring had been hacked away, what can i do to make my stock tach work? I dont know what the original connector looks like plus my car is originally an 2.8, now a 357..i honestly dont know where to start but I would love to retain the stock gauge cluster.

 

Find the stock tach wire, and hook it up to your current distributor.

A 6-cyl tach won't work right with a V8. A 6-cyl dist produces 3 pulses (sparks) per crank rev, whereas a V8 one produces 4. The tach will read 33% high, even if it's "accurate" (unlike virtually all of the stock units for our cars).

The good news is, a V8 cluster will bolt right up to where your 6-cyl one is now. Then all ya gotta worry about is fixing the almost certainly broken tach in it.

 

White wire IIRC right?

 

In later years, yes. Earlier years, it was tan. I think 85 was still tan but don't hold me to it.

 

Yeah like Sofa said, the V6 tach will not work with a V8 engine. The V6 tach will read high..

If you need a V8 cluster, I have one in a '91 rs and a '92 z28.. PM me if interested.