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#1 |
Registered User
![]() Join Date: Dec 2012
Location: Los Banos CA
Posts: 2,705
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Factory Tach question
Hello guys, i have been searching and found answers to if the factory tach works or what you have to get it to work with a filter.
my problem is I have a new HEI Distributor and installed a factory tach but when at 2000 RPM's it reads about 300 or so? Any idea what I need to do?
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1956 Chevy Bel Air 2 door 1956 Chevy 210 4 Door 1970 K20 LWB project the Hulk build w/Supercharged 4.8L-ly2/4L60E HULK BUILD 1970 C10 Yellow/White Deluxe LWB w/ 5.3L-LC9/6L80E 1968 K10 LWB Dark green my son calls it "THE HULK Jr"HULK JR *SOLD* GO ![]() |
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#2 |
Registered User
![]() Join Date: Aug 2013
Location: Atlanta, GA
Posts: 702
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Re: Factory Tach question
Have you verified you have the right tach. Are you running a V8/V6?
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1968 C10 292/3 spd - sold 1969 K10 350/3 spd/205 - sold 1971 K5 350/4 spd/ 205 - sold 1970 K20 350/350/205 - sold 1969 K20 396/400/205 - work in process |
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#3 |
Registered User
![]() Join Date: Dec 2012
Location: Los Banos CA
Posts: 2,705
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Re: Factory Tach question
Sorry yes it is a V8 tach cluster out of a c50. It has the red v8 description on the back. The problem I am having is that it moves when you rev it up but only slightly.
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1956 Chevy Bel Air 2 door 1956 Chevy 210 4 Door 1970 K20 LWB project the Hulk build w/Supercharged 4.8L-ly2/4L60E HULK BUILD 1970 C10 Yellow/White Deluxe LWB w/ 5.3L-LC9/6L80E 1968 K10 LWB Dark green my son calls it "THE HULK Jr"HULK JR *SOLD* GO ![]() |
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#4 |
Registered User
Join Date: Aug 2006
Location: Redmond, WA
Posts: 6,332
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Re: Factory Tach question
I don't know about the factory originals but all of the aftermarket ones I've seen disclaim "NOT compatible with HEI" for some reason. I do not know the reason - though mine works with Pertronix ignition, I can't swear as to how accurate it is.
Worst case Dakota Digital (and others too no doubt) make a cheap tach adapter you can buy that will take most signals and filter+adapt them and probably be able to drive the tach.
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1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible |
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#5 |
Senior Member
![]() Join Date: Mar 2012
Location: Royston, Ga
Posts: 625
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Re: Factory Tach question
Unless it is damaged it should work just fine with an hei just it may bounce a little, the filter I believe will help curb that.
Now from my own experience with a factory tach, mine worked just fine with an original, obviously newer, hei but only after I realized that I had it hooked up backwards. ![]() Check and make sure you have the wires running to the correct place, should be labeled on the back of the tach, and go from there. When mine was hooked up backwards, it did just about like you said yours does, stays low rpms and barely moves.
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Evan - 1969 C10 LWB fltsd 307 3spd man.steer 3.73 rear orig.white/turquoise poly with drk turquoise int - 1972 Custom Deluxe10 LWB fltsd 350/TH350 pwr. steer/brks A/C 3.07posi rr orig.med blue with blue cloth trim. Last edited by 1969guy; 06-08-2016 at 11:05 PM. |
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#6 |
Registered User
Join Date: May 2016
Location: Waverly, NE
Posts: 338
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Re: Factory Tach question
I've read on here somewhere that the module in the HEI can make a difference. The recommendation was to only us a GM (AC/Delco) module to get the tachs to read right. I have a non-AC/Delco module and my reproduction tach reads just fine, but you said yours is a factory one so I could be all wet. If you are interested, my module is Standard brand.
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1965 Malibu SS L79 Restoration Page 1965 Two-Door Wagon Project Progress Page 2006 Pontiac GTO Preservation Project Rich Cummings |
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#7 |
Registered User
![]() Join Date: Dec 2012
Location: Los Banos CA
Posts: 2,705
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Re: Factory Tach question
Thanks guys for the information. I am going to try and switch the wires and see if that works. That will be the first and easiest step. I will report back. But any other idea please post away. M
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1956 Chevy Bel Air 2 door 1956 Chevy 210 4 Door 1970 K20 LWB project the Hulk build w/Supercharged 4.8L-ly2/4L60E HULK BUILD 1970 C10 Yellow/White Deluxe LWB w/ 5.3L-LC9/6L80E 1968 K10 LWB Dark green my son calls it "THE HULK Jr"HULK JR *SOLD* GO ![]() |
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#8 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,647
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Re: Factory Tach question
I had my old Sun tach (Super II, iirc) since before I converted to HEI back in the Eighties. No problems before the switch.... or after. Pretty sure it has the original AC/Delco module if that matters.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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