Stock tach with GM style HEI

[Odmark]

Hello! I figure its best to make a separate thread on this subject

So i have a "GM Style" HEI Distributor, and when i plug in my stock tach the car dies.

I know why this happens, but is there some fix for this?

I have read something avout some kind of filter?

 

[turtle5353]

There's your problem...... your car is allergic to GM!!!

 

[Thomas]

Hello! I figure its best to make a separate thread on this subject

So i have a "GM Style" HEI Distributor, and when i plug in my stock tach the car dies.

I know why this happens, but is there some fix for this?

I have read something avout some kind of filter?

I had to get a tach adapter (MSD PN 8920) to get the org tachometer to work with msd distributor and 6Al box. Can also work for you maybe.

Just a suggestion / idea.

// Thomas

 

[Hemikiller]

The HEI cap has a "tach" terminal that you can plug an MSD adapter into. I believe since the dizzy is a magnetic triggered unit, you'll need #8920. However, I would contact MSD to verify before spending my money.

https://www.msdperformance.com/products/accessories/tach_adapters/parts/8920

 

[mustang7173]

Odmark,

I want to check back with you to see how the HEI unit was working for you. I purchased the TSP HEI for the Ford 302 V8.

Several reason I chose to buy it was the cap terminals, coil located on the top which eliminates an external coil and wires. I do have to purchase the Mallory HEI KIT P/N 29008 to connect my Mallory 6A Hyfire box.

One thing I need to check is the housing to intake manifold clearance. The other issue that I see , is the stock air cleaner clearance.

Depending on my research, I may or may not swap out the distributors.

Please lets us know.

mustang7173 :thankyouyellow:

 

[Odmark]

I have been in contact with MSD and they have nothing that can fix my problem, and i also talked to another company (Of course i dont remember their name right now) and they told me the same thing. Its impossible.

So right now im running a stand alone Tach with a shift light, but in the future im going full MSD so i can use the original tach.

mustang7173:

I have actually been very pleased with these distributors, i ran one on my big block olds before as well and worked like a charm.

Drawbacks is the tachometer issue, as well as the size.

On clearences... when i bought my HEI, i had the 4V edelbrock performance intake (yes on my 2v heads, i did not install it), an edelbrock 600 and a 14" air filter.

I had to grind a little bit on the intake to get the distributor to move freely, as well as replacing the 14" filter with a triangular edelbrock Pro-Flo because the filter hit the dist otherwise.

Now i have a Holley Street Dominator (not the best intake i know, but at least its for 2v heads. And i got it diiirt cheap) and a holley 650 double pumper. And now the distributor does not hit the intake and i run a 14" filter again with no issues.

So its all down to the intake. If the air filter does not clear you can always space it up, but if it hits the intake you have to take material off it.

 

[TheRktmn]

M7123T: 1971-1973 Ford Mustang Tachometer Conversion

My tachometers work with HEI systems.

http://www.rccinnovations.com/index.php?show=menu-mustang-all#tachs

 

[Jeff73Mach1]

I changed out my tach this summer . . . but I had been running the HEI with the original wiring and my tach actually worked and was pretty accurate. The resistor wire (Pink) was cut and replaced with regular wire to get 12 volts and no tach wire was used.

It isn't supposed to work-it shouldn't be accurate-but dammit -it did and it was for over 5 years

 

[mudbilly]

My car was originally a non-tach version. I had the tach I bought off Ebay re-wired by "the tach man" into a 3 wire. +, -, tach.

All I had to do was crimp on a /14" fast-on and it plugged right into my HEI. Add 12v & ground and off to the races...

http://www.tachman.com/

He also calibrates the needle position.

Here's a funny story though, At first I couldn't get it to work, :chin: and went round and round thinking that I had wired in in wrong, :huh: or broke it during installation :-/. He had sent the paperwork with a picture showing it worked fine at his shop... I was going out of my mind, and then I finally noticed that the needle had fallen onto the wrong side of the little metal pin that stops the spring from taking it backwards past zero. It was sitting right on the wrong side of the pin with the engine off........rofl ......had to take it back out and carefully move the needle to the right side :shootself:

 

[mustang7173]

Hello Odmark,

After I got it home, I begin to look at the Air Gap intake I have and wonder, wow, this may not be the best solution for my application. Then, I am using the bottom part of my air cleaner with a K & N air filter and that is going to be an issue. Plus, I have an Mallory 6A to install with means a new harness kit for the module.

So, my current Mallory Unlite is dialed in, along with the factory tach setup, and plus adding the 6A would be a breeze.

So, I may put this distributor on E-Bay.

Thanks,

mustang7173 :thankyouyellow:

I have been in contact with MSD and they have nothing that can fix my problem, and i also talked to another company (Of course i dont remember their name right now) and they told me the same thing. Its impossible.

So right now im running a stand alone Tach with a shift light, but in the future im going full MSD so i can use the original tach.

mustang7173:

I have actually been very pleased with these distributors, i ran one on my big block olds before as well and worked like a charm.

Drawbacks is the tachometer issue, as well as the size.

On clearences... when i bought my HEI, i had the 4V edelbrock performance intake (yes on my 2v heads, i did not install it), an edelbrock 600 and a 14" air filter.

I had to grind a little bit on the intake to get the distributor to move freely, as well as replacing the 14" filter with a triangular edelbrock Pro-Flo because the filter hit the dist otherwise.

Now i have a Holley Street Dominator (not the best intake i know, but at least its for 2v heads. And i got it diiirt cheap) and a holley 650 double pumper. And now the distributor does not hit the intake and i run a 14" filter again with no issues.

So its all down to the intake. If the air filter does not clear you can always space it up, but if it hits the intake you have to take material off it.

 

[mustang7173]

Hello Jeff73Mach1,

What tach do you have now? Could you tell any difference in the way the HEI worked after replacing the Pink Wire?

mustang7173

I changed out my tach this summer . . . but I had been running the HEI with the original wiring and my tach actually worked and was pretty accurate. The resistor wire (Pink) was cut and replaced with regular wire to get 12 volts and no tach wire was used.

It isn't supposed to work-it shouldn't be accurate-but dammit -it did and it was for over 5 years

 

[mustang7173]

Hello mudbilly,

Well, Oh Right, Oh Right , Oh Right! Glad to see you got everything running as it should. I do like the style terminals on the HEI. I do belive in the long run, I will have intake clearance along with air cleaner housing clearance problems.

Thank You!

mustang7173 :thankyouyellow:

My car was originally a non-tach version. I had the tach I bought off Ebay re-wired by "the tach man" into a 3 wire. +, -, tach.

All I had to do was crimp on a /14" fast-on and it plugged right into my HEI. Add 12v & ground and off to the races...

http://www.tachman.com/

He also calibrates the needle position.

Here's a funny story though, At first I couldn't get it to work, :chin: and went round and round thinking that I had wired in in wrong, :huh: or broke it during installation :-/. He had sent the paperwork with a picture showing it worked fine at his shop... I was going out of my mind, and then I finally noticed that the needle had fallen onto the wrong side of the little metal pin that stops the spring from taking it backwards past zero. It was sitting right on the wrong side of the pin with the engine off........rofl ......had to take it back out and carefully move the needle to the right side :shootself:

 

[Jeff73Mach1]

I now have a 10,000 rpm stepper motor tach by Marshall with recall and shift light-works great and altering the housing to fit it wasn't a huge battle.

In fairness, the wiring for the HEI was done by a buddy's shop who I used to let do some stuff on my car. I completely eliminated that part of the circuit and run off an auxiliary switched fuse block now with a memory power wire to retain settings.

With the HEI the stock tach was sluggish to react below about 750 rpm and lost it's shit over 6200 rpm and started getting really bouncy, but for typical driving it worked fine. As I said HEI and stock tachs should not work together, but it did.

 

[EvilPuppetMaster]

Hi guys,,

My first post here... I just want to let you know that replacing pink resistor wire with solid copper wire works great with hei distributor and original mach 1 tach

I just did a quick test and it worked great.

I might do a quick YouTube video later tonight of it running

Alex

Sent from my ONE A2005 using Tapatalk

 

[EvilPuppetMaster]

Hi guys,,

My first post here... I just want to let you know that replacing pink resistor wire with solid copper wire works great with hei distributor and original mach 1 tach

I just did a quick test and it worked great.

I might do a quick YouTube video later tonight of it running

Alex

Sent from my ONE A2005 using Tapatalk

Here you go... Quick and dirty



My test is wired like this

Battery 12 v - - - - tach------ Batt terminal on Hei distributor

Tach output on hei distributor is not used in this case.

I know car runs like crap but that is going to be another thread...

Cheers

Alex

Sent from my ONE A2005 using Tapatalk

 

[mustang7173]

Hi guys,,

My first post here... I just want to let you know that replacing pink resistor wire with solid copper wire works great with hei distributor and original mach 1 tach

I just did a quick test and it worked great.

I might do a quick YouTube video later tonight of it running

Alex

Sent from my ONE A2005 using Tapatalk

Here you go... Quick and dirty

Alex,

Nice! One question. The wire from battery,crimped together to the tach is connected to the exposed terminal? So the tach is reading from the one wire?

Mustang7173

 

[mudbilly]

Hello mudbilly,

I do like the style terminals on the HEI. I do belive in the long run, I will have intake clearance along with air cleaner housing clearance problems.

Thank You!

mustang7173 :thankyouyellow:

My air filter is stepped back. It came with the engine, so I don't know what it is or where it is sourced from. But it fits great.

 

[EvilPuppetMaster]

Here you go... Quick and dirty



My test is wired like this

Battery 12 v - - - - tach------ Batt terminal on Hei distributor

Tach output on hei distributor is not used in this case.

I know car runs like crap but that is going to be another thread...

Cheers

Alex

Sent from my ONE A2005 using Tapatalk

Alex,

Nice! One question. The wire from battery,crimped together to the tach is connected to the exposed terminal? So the tach is reading from the one wire?

Mustang7173

Hi,

These original tachometers are operating based on the current fluctuation .

So +12 volts is connected to one terminal on the tach, then from another tach terminal it is connected to the batt post on HEI distributor.

So , when its idling, the tach is recording frequency going trough it and moves the needle accordingly...Step on the throttle, and Hei turns faster and frequency changes and the needle goes up....

That's all there is to it.

This logic only applies to the old 2 wire tachometers. New tachometers read specific signal sent by tach terminal on HEI which is then decoded in the tachometer ... they usually have 3 or more terminals...

Pink wire connected to original tach in your mustang is resistance wire... It drops 12 volt to 7 volts. It would cause lots of issues if you were to attach it to the batt terminal on HEI

HEI Needs switched 12 volts. So replace pink resistance wire with solid copper wire and plug it to the batt terminal on hei and your tach should work just fine.

Here is the sample diagram. + on ignition coil corresponds to BATT terminal on HEI

Alex

 

[mustang7173]

Hello Alex,

Cool! Thank you!

mustang7173