HEI and A factory tac - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Patg · 11-10-2008, 08:22 PM

Has any one had a issue with installing a factory tac with a HEI distributor?
I installed a used one and at idle everything reads ok. But as the RPMs go up the error gets larger. I know this because I had a autometer tac and it wiorked fine. Somewhere I think read that there may be a issue with using a hei distributer on a factory tac.
The bottom line is should just go and buy a new tac or would I just be wasting my money?

Lastly the adjustment pot on the back of the factory tac can that be used to calberate it.

Thanks

**LockDoc** · 11-10-2008, 08:40 PM

-
I just put one in a '72 GMC with HEI, no problems on it.... I don't think you can get a lot of adjustment out of the pot. maybe someone else will have some other ideas for you.

Oh, and

.

LockDoc

**leddzepp** · 11-10-2008, 08:41 PM

I am running HEI with a factory tach, no problems so far, and it has been several years now.

**kwmech** · 11-10-2008, 08:42 PM

Mine works just fine also---no issues

JimKshortstep4x4 · 11-10-2008, 08:54 PM

We have several tachs with HEI and they have worked well for years.

Jim

72Levi · 11-10-2008, 11:19 PM

You may have some bad resisitors on your Tach, they are 36+ yrs old and they do go out.

jorgensensc · 11-11-2008, 10:39 AM

Are you positive you have the correct tach for the engine, V8 and 6 cylinder tachs, are different.
Shawn

Longhorn Man · 11-11-2008, 06:14 PM

lets not forget, these tachs were not real acurate 40 years ago...

Blazer1970 · 11-12-2008, 07:48 AM

Quote:

Originally Posted by Longhorn Man

lets not forget, these tachs were not real acurate 40 years ago...

And they have gotten a lot worse over the years. I have heard that it is the capacitors that drift over time.

eightbanger · 11-12-2008, 09:40 AM

Mine works just fine also.

But take jorgensensc advice and check the stamp on the back to see if it's the right one.

jorgensensc · 11-12-2008, 11:43 AM

Dang Longhorn, you get the credit for everything!

eightbanger · 11-12-2008, 03:54 PM

Quote:

Originally Posted by jorgensensc

Dang Longhorn, you get the credit for everything!

It's the names they're just so similar...jorgensensc, Longhorn Man

I'm sorry jorgensensc, it's been a long hard week.

**leddzepp** · 11-12-2008, 04:21 PM

Quote:

Originally Posted by jorgensensc

Dang Longhorn, you get the credit for everything!

And it is well deserved...just look at all the posts and knowledge that Andy has contributed to this board!

eightbanger · 11-12-2008, 04:58 PM

Quote:

Originally Posted by leddzepp

And it is well deserved...just look at all the posts and knowledge that Andy has contributed to this board!

Just to clarify, I had to edit my first post as I credited Andy for sugesting he check to see if it were the correct Tach. When it was jorgensensc.

Longhorn Man · 11-12-2008, 05:07 PM

LOL!
A LOT of the info that I have, came from THIS board.

jorgensensc · 11-12-2008, 06:38 PM

Oh Geez!! I meant it as a joke, and now you guys have made me feel like a real a$$! And to think, I wasa on here with Longhorn Man when he was just a wee little Longhorn Boy with a mere 20k posts! Ha.
SHawn

**leddzepp** · 11-12-2008, 06:51 PM

A lot of info on here does get recycled...just makes it easier to find when you need it. Everybody here contributes...just that I haven't seen anyone else with 70K posts! No offense was intended towards anybody.

jorgensensc · 11-12-2008, 06:57 PM

None was taken! It was all a bit of a joke.

Huck · 11-12-2008, 07:03 PM

The wave length of the signal is different between HEI and original ignition which the tach's were designed to work with. There are some things that can be done but---reality is that in stock form, they are far from accurate. If it is within a hundred or so rpm, consider it OK for driving purposes. You can tweek the pot on the back for closer readings, but realize when you go one way, you are flipping readings on the other end. Huck

Patg · 11-16-2008, 12:58 AM

thanks all for your input I think I will be buying a new factory tac and see what happens

11-10-2008, 08:22 PM	#1
Patg Registered User Join Date: Nov 2005 Location: Nevada Posts: 7	HEI and A factory tac Has any one had a issue with installing a factory tac with a HEI distributor? I installed a used one and at idle everything reads ok. But as the RPMs go up the error gets larger. I know this because I had a autometer tac and it wiorked fine. Somewhere I think read that there may be a issue with using a hei distributer on a factory tac. The bottom line is should just go and buy a new tac or would I just be wasting my money? Lastly the adjustment pot on the back of the factory tac can that be used to calberate it. Thanks __________________

11-10-2008, 08:40 PM	#2
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,334	Re: HEI and A factory tac - I just put one in a '72 GMC with HEI, no problems on it.... I don't think you can get a lot of adjustment out of the pot. maybe someone else will have some other ideas for you. Oh, and . LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - Last edited by LockDoc; 11-10-2008 at 08:40 PM.

11-10-2008, 08:41 PM	#3
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,989	Re: HEI and A factory tac I am running HEI with a factory tach, no problems so far, and it has been several years now.

11-10-2008, 08:42 PM	#4
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,397	Re: HEI and A factory tac Mine works just fine also---no issues

11-10-2008, 08:54 PM	#5
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: HEI and A factory tac We have several tachs with HEI and they have worked well for years. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

11-10-2008, 11:19 PM	#6
72Levi Active Member Join Date: Feb 2006 Location: sa tx Posts: 851	Re: HEI and A factory tac You may have some bad resisitors on your Tach, they are 36+ yrs old and they do go out. __________________ 1972 K5 Blazer ALL ORIGINAL paint & engine, A/C, Tilt, 4sp, AM/FM, Tow Hooks, Aux Battery Tray, Tach, Vacuum 2004 FORD FX4 SuperCrew 2005 CTS-V 12 sec family car 2008 Buick Enclave AWD, Nav, & DVD, Wife LOVES it!

11-11-2008, 10:39 AM	#7
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Re: HEI and A factory tac Are you positive you have the correct tach for the engine, V8 and 6 cylinder tachs, are different. Shawn __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-11-2008, 06:14 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: HEI and A factory tac lets not forget, these tachs were not real acurate 40 years ago...

11-12-2008, 09:40 AM	#10
eightbanger 454 MAKES IT ROAR Join Date: Jan 2008 Location: Essex, U.K Posts: 2,701	Re: HEI and A factory tac Mine works just fine also. But take jorgensensc advice and check the stamp on the back to see if it's the right one. __________________ Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger Last edited by eightbanger; 11-12-2008 at 03:49 PM.

11-12-2008, 11:43 AM	#11
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Re: HEI and A factory tac Dang Longhorn, you get the credit for everything! __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-12-2008, 05:07 PM	#15
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: HEI and A factory tac LOL! A LOT of the info that I have, came from THIS board.

11-12-2008, 06:38 PM	#16
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Re: HEI and A factory tac Oh Geez!! I meant it as a joke, and now you guys have made me feel like a real a$$! And to think, I wasa on here with Longhorn Man when he was just a wee little Longhorn Boy with a mere 20k posts! Ha. SHawn __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-12-2008, 06:51 PM	#17
leddzepp Moderator Join Date: May 2007 Location: Southern Cal Posts: 19,989	Re: HEI and A factory tac A lot of info on here does get recycled...just makes it easier to find when you need it. Everybody here contributes...just that I haven't seen anyone else with 70K posts! No offense was intended towards anybody. Last edited by leddzepp; 11-12-2008 at 06:53 PM.

11-12-2008, 06:57 PM	#18
jorgensensc Registered User Join Date: Jul 2003 Location: Cypress, Tx Posts: 4,005	Re: HEI and A factory tac None was taken! It was all a bit of a joke. __________________ 1972 C20 Suburban- Big Blue Betty '56 Chevy Bel Air Sedan- Frame up Restoration -What would you attempt to achieve if you knew you could not fail?- -I Refuse To Tiptoe Through Life, Only To Arrive Safely At Death's Door- R.I.P. EAST SIDE LOW LIFE

11-12-2008, 07:03 PM	#19
Huck Senior Member Join Date: Jun 2001 Location: Shelbyville, KY Posts: 3,269	Re: HEI and A factory tac The wave length of the signal is different between HEI and original ignition which the tach's were designed to work with. There are some things that can be done but---reality is that in stock form, they are far from accurate. If it is within a hundred or so rpm, consider it OK for driving purposes. You can tweek the pot on the back for closer readings, but realize when you go one way, you are flipping readings on the other end. Huck



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11-16-2008, 12:58 AM	#20
Patg Registered User Join Date: Nov 2005 Location: Nevada Posts: 7	Re: HEI and A factory tac thanks all for your input I think I will be buying a new factory tac and see what happens __________________

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