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#1 |
what happened to flint mi
Join Date: Oct 2005
Location: san diego
Posts: 437
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hei stock tach ,how far off is the reading?
does any body know how to make a factory tach work accurately with a hei? how far off is it ? any one ? any one??
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71 swb 2wd fleet frame off in progress 72 4x4 blazer daily driver 70 olds cutlass s mint condition owned by a grandma 56 gmc 2wd project waitng 97 fiance mobile |
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#2 |
Truck junkie
![]() Join Date: May 2006
Location: Reno NV
Posts: 697
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Re: hei stock tach ,how far off is the reading?
There are a few places that will set up your tach to work with the HEI. I don't know how far off it is I have just read a bunch of posts on the subject on other sites. I have always wondered if a guy could wire in a radio shack potentiometer (adjustable resistor) and a temporary tach and adjust the potentiometer to match the factory tach to the temp tach. I have no clue if this can be done just something I have wondered.
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#3 |
its all about the +6 inches
Join Date: Jan 2001
Location: Hilliard Ohio
Posts: 2,693
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Re: hei stock tach ,how far off is the reading?
it should read fine...assuming your 35 year old tach is acurate.
A tach is a tach, doesn't matter if you have points or HEI. |
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#4 |
Senior Member
Join Date: Mar 2006
Location: bay area, ca
Posts: 305
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Re: hei stock tach ,how far off is the reading?
longhorn is right just plug and play...just did it a month ago
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#5 | |||
Union Electrician
Join Date: Feb 2005
Location: Louisville, Ky.
Posts: 3,356
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Re: hei stock tach ,how far off is the reading?
Yep, all the repopers say their tachs won't work with HEI and I have personally tested well over 150 repop tachs and all have worked fine with HEI. I think the tachs are accurate enough but not perfect,and I haven't had the chance to hook two up at the same time to check them against a factory tach or another type of tach for that matter.
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#6 |
Senior Member
![]() Join Date: Aug 2005
Location: Los Angeles
Posts: 1,333
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Re: hei stock tach ,how far off is the reading?
Don't know that HEI would cause a problem with either an original tach. or a reproduction, but an MSD or any other multiple spark discharge ignition will.
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1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90. |
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#7 |
Oilfield Trash
Join Date: Sep 2003
Location: Raymore, Sk, Canada, Earth
Posts: 3,171
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Re: hei stock tach ,how far off is the reading?
So is their anyway to make it work an msd style ignition?
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14 Dodge 3500 Mega Cab 08 Dodge 3500 Mega Cab 87 Chev 3+3 4x4 80 GMC K10 High Sierra bone stock 70 Chevelle 350SS long term project 68 GMC 3ton Grain Truck/Garbage wagon 50 Pontiac 2 Door Coupe Project "I've got a shotgun rifle and a 4 wheel drive and a country boy can survive" Hank Jr. |
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#8 |
what happened to flint mi
Join Date: Oct 2005
Location: san diego
Posts: 437
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Re: hei stock tach ,how far off is the reading?
well a while ago i asked a speedo shop about it and they said they would have to make a" special " harness to work with the hei and the factory tach . is this special harness nothing more than a plug for the tach and a plug for the hei batt and tach (like the plug i nabbed today at the bone yard ??)oh and the speedo place said they would charge me "only 125 dollars " geee thanks for nuthin !
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71 swb 2wd fleet frame off in progress 72 4x4 blazer daily driver 70 olds cutlass s mint condition owned by a grandma 56 gmc 2wd project waitng 97 fiance mobile |
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#9 |
Senior Member
Join Date: Nov 2005
Location: northwestern wi
Posts: 2,111
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Re: hei stock tach ,how far off is the reading?
so do the factory tachs last wired to a hei? i thought i read a post awhile back on here that they would not last without burning out but i don't know why but then again i know very little about electronics
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common sense isn't so common anymore |
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#10 |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,811
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Re: hei stock tach ,how far off is the reading?
I had always thought the pot that is accessable from the back of the tach is for adjustments
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Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
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#11 | |||
Union Electrician
Join Date: Feb 2005
Location: Louisville, Ky.
Posts: 3,356
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Re: hei stock tach ,how far off is the reading?
Richard you are right, you can calibrate them some.
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#12 |
Senior Member
![]() Join Date: Mar 2000
Location: Saskatoon,SK,Canada
Posts: 2,476
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Re: hei stock tach ,how far off is the reading?
I have run my stock oe factory tach with hei and msd. No problems. I checked it against a tach in my digital volt meter and while it was not killer accurate it wasn't more than a couple hundred rpm out in it's worst case. I have about 10 years of straight hei to fact tach with no problems and about 3 years of msd to factory tach with no problems. I believe that adjustment pot on the back is used to set the tach to zero isn't it?
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Saskatoon, Saskatchewan Canada |
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#13 |
Active Member
Join Date: Mar 2004
Location: Virginia
Posts: 169
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Re: hei stock tach ,how far off is the reading?
Not sure if this helps, but my factory tach with HEI reads 400 RPM faster than it really is.
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71 Blazer CST 72 K20 Capt USAF |
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#14 | |||
Union Electrician
Join Date: Feb 2005
Location: Louisville, Ky.
Posts: 3,356
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Re: hei stock tach ,how far off is the reading?
they you reach around to the back of the dash with a small flat head or phillips I can't remeber which one and turn the little screw in the back of the tach until you get the right reading. This is how they are calibrated
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