Adding a tach with HEI on an L31 Vortec engine - did I mess up?

[msg]

This maybe a question for the engine forum but I have a cluster that I added a tach that I bought from Classic Auto Parts here. (EDIT: Actually this was purchased from Truck and Car Shop OC on Ebay --see post #4 below)

I am also rewiring with the American Auto Wire kit for my 66 C10 and thought I needed to add a filter and wasnt sure how to wire it. I called AAW and they weren't sure how to wire the filter in specifically because there isnt any install notes to know what wire feeds what on the Classic Auto Parts filter. I tried calling Classic but they are closed due to inclement weather.

This was the filter I thought I needed to use, but now I wonder if the tach is even gonna work at all since I have an HEI distributor.

If anyone has added that tach to their cluster with an HEI please let me know what was done to make it work. Thanks.

[Nanook]

I think the filter is only required for a LS conversion. If you are using a HEI then the filter is not required and I believe the HEI has a "tach" connection point.

[62bagger]

I have a similar tach that I got from Car and truck shop. and it has not worked right from day one. I have HEI as well. this thing only revs to 2500 and does not return to zero when the engine is off. I am interested to see someone has had and solved these issues.
I had not considered a filter. I have checked the wiring and made sure there is a good ground.

[msg]

I purchased this tach so many years ago I forgot that it was not Classic Parts but the Truck and Car Shop off of eBay. I went back through my emails from Ebay and found the message thread with the seller before I purchased it. See below.

MSG
I was looking for a tach that will work with my 1966 Chevy C10 truck that will have an L31 engine and an HEI distributor. I am also updating the wiring harness with one from American Auto wire. Are there any specs on the internals of this tach that counterpart can share? I just want to be sure it will work with my setup. Thanks.

Truck & Car Shop
They do not have any of that info, but i can tell you that HEI is nothing special and still has a coil, and that is where the tach gets its pulse

MSG
Ive seen some tachs that look identical to this that are listed as non compatible with HEI. Something about the frequency doesnt transmit properly and a filter is needed to help. Just wanted to be sure before spending over $200.

Truck & Car Shop
ok, i cannot speak on those tachs behalf but ours is fine with systems that have a coil....those others may have some sort of late model technology inside but ours is made as original to work with original systems, yours is not original but HEI did not alter too far from original
HOWEVER..... it should work fine if you are using a GM distributor from a OE donor car, the exception is if you are using some companies aftermarket copy of GM's original HEI distributor (like MSD, ACCEL, etc...) now those may have some sort of proprietary system that may need a special device to send a proper signal to the tach , you follow??

MSG
I do follow and thanks for the quick replies..particularly this part "ours is made as original to work with original systems"

When I spoke with American Autowire the tech said that the wiring harness was designed to the original specs so if the tach is original there will be no issue. He said as long as the internals were factory style then all is well.

The distributor I was going to reuse was a delco remy which I think was used on GM autos. Ill attach a pic


Truck & Car Shop
you should be fine with that OE distributor



After that discussion I purchased the tach and did not get the filter. The truck is still being wired up and not in working condition.

[62bagger]

I have tuned port injection with an ECU. That might be the issue on my end.
I'll try classic parts to see if they have information on that filter for my ignition. I'm not real positive though. Usually, these resellers don't have much info on the parts they sell. I'm surprised you got so much from car and truck shop.

[62bagger]

I spoke to classic parts and they don't offer tech support, but they gave me the supplier, classic instruments. The filter is for use with an HEI distributer. The tach is set up for the old-style points distributer and the high voltage signal from the HEI is more than the tach can take. We will see if this works for my truck if I haven't destroyed the tach already by not having this filter.

[msg]

Thanks for sharing that, Im a ways off before turning a key but I hope by then I can figure things out on that filter in my scenario. Im pretty sure that tach I bought was the same manufacturer as Classic Parts sells. The description of that filter says its needed for a computer controlled LS engine which I dont have.