Factory tach question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**70shortfleet** · 09-23-2010, 10:15 PM

Does anyone know if a factory tachometer will work with an HEI distributor?

VA72C10 · 09-23-2010, 10:28 PM

yes...I had it on my blazer. There is a spot to run the tach wire on the distributor cap.

Blazer1970 · 09-24-2010, 06:10 AM

Just be forewarned that a factory tach will not be anywhere near accurate, no matter what kind of ignition you have.

red71cheyenne · 09-24-2010, 03:20 PM

Quote:

Originally Posted by Blazer1970

Just be forewarned that a factory tach will not be anywhere near accurate, no matter what kind of ignition you have.

Not arguing, but why would you say that? They are both using the pulses from the coil for a signal. Why would one be more accurate than the other?

**1970cstblazer** · 09-24-2010, 03:29 PM

Mine reads about 100 rpm too much throughout the sweep.

red71cheyenne · 09-24-2010, 03:49 PM

Quote:

Originally Posted by 1970cstblazer

Mine reads about 100 rpm too much throughout the sweep.

Have you tried mechanically zeroing it? There is a zero adjust on the back.

**too much stuff** · 09-24-2010, 03:28 PM

Quote:

Originally Posted by Blazer1970

Just be forewarned that a factory tach will not be anywhere near accurate, no matter what kind of ignition you have.

I can't agree with that statement. I have seen some that read quite accurate. I have also seen some that were not close.

To answer your question,
Yes it will work with an HEI.

Longhorn Man · 09-24-2010, 09:53 PM

I think what blazer1970 was trying to say, is these original tachs were inacurate 40 years ago, and are worse now.
Back to the original question, some people have had stock tachs that wouldn't work with the HEI, but in general, they usually work.

*sharpie1972* · 09-24-2010, 09:59 PM

Mine works just fine up to 5k! Sharpie

Andy4639 · 09-24-2010, 10:32 PM

The factory HEI setup has the terminal marked for a tach.
Mine works great for the past 20 some years on the HEI and it's as acurate today as it was when I bought it. These are 70's technolgy but very good I may say. I have had it hooked up to numerous machines and it was within a 100RPM of any one of them which is pretty dog gone good I'd say!
I even have a hand held tach to use back when I had the stock 307 in it and it always read the same.

09-23-2010, 10:15 PM	#1
70shortfleet Senior Member Join Date: Apr 2010 Location: St.Peters, MO Posts: 2,247	Factory tach question Does anyone know if a factory tachometer will work with an HEI distributor?

09-23-2010, 10:28 PM	#2
VA72C10 VA72C10 Join Date: Mar 2008 Location: Midlothian, VA Posts: 25,267	Re: Factory tach question yes...I had it on my blazer. There is a spot to run the tach wire on the distributor cap. __________________ Looking for a 67-72 swb or blazer project in or around VA. Last edited by VA72C10; 09-23-2010 at 10:28 PM.

09-24-2010, 06:10 AM	#3
Blazer1970 Registered User Join Date: Dec 1999 Location: Old Mission, MI, USA Posts: 2,507	Re: Factory tach question Just be forewarned that a factory tach will not be anywhere near accurate, no matter what kind of ignition you have. __________________ Tim

09-24-2010, 03:29 PM	#5
1970cstblazer All stock and staying that way Join Date: Jul 2003 Location: Elkland, PA Posts: 1,967	Re: Factory tach question Mine reads about 100 rpm too much throughout the sweep. __________________ 1970 K/5 Blazer CST 4WD, TOTM winner December 2024! Medium Bronze, 93k ACT. miles, 350, 4 speed, rear positraction, 16.5" x 8.25" HD Kelsey Hayes wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration finally getting close to completion.. 1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor... 2017 Sierra 1500 SLT 4WD, Black, 45k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2... 2019 Canyon SLT 4WD, White, 62k miles, 3.6, 8L45, 3.23 LS, 18" wheels

09-24-2010, 09:53 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Factory tach question I think what blazer1970 was trying to say, is these original tachs were inacurate 40 years ago, and are worse now. Back to the original question, some people have had stock tachs that wouldn't work with the HEI, but in general, they usually work.

09-24-2010, 09:59 PM	#9
sharpie1972 Account Suspended Join Date: Apr 2007 Location: Powell, Wyoming Posts: 4,973	Re: Factory tach question Mine works just fine up to 5k! Sharpie

09-24-2010, 10:32 PM	#10
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Re: Factory tach question The factory HEI setup has the terminal marked for a tach. Mine works great for the past 20 some years on the HEI and it's as acurate today as it was when I bought it. These are 70's technolgy but very good I may say. I have had it hooked up to numerous machines and it was within a 100RPM of any one of them which is pretty dog gone good I'd say! I even have a hand held tach to use back when I had the stock 307 in it and it always read the same. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.



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