Author Topic: tach question  (Read 117 times)

1sgtretired

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tach question
« on: October 09, 2018, 09:57:08 AM »
 72 TA, originally came with the unitized ignition.  When I purchased the car it had an MSD distributor set up installed.  Also, when I purchased the car the tach didn't work.  Long story short I replaced the MSD set with a HEI system.  Figuring out the wire mess I had I traced the brown wire from the tach into the engine compartment part of the wire was replaced with a different color wire.  Found the shaker wire taped up in a bundle.
The question does the tach have to be calibrated to the HEI distributor?  The tach currently shows idle at about 750 RPMs but when revving the engine the tach only will go to 2000 RPMs.
My next though was to hook up a tach and dwell meter and check it that way after 8 hours had to take a break.

Any thoughts would be appreciated. 
USAF 1st Sgt Retired

1970 RAM AIR III TA. White
1972 455 HO, Blue
1973 Formula, Functional Ram Air set up
1973 455 TA, Red
1976 400 TA sold
1978 Black W-72 TA
2006 Chevy 2500 HD Turbo Diesel
2011 3500 Chevy Turbo Diesel
2012 BMW X5

firebirdparts

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Re: tach question
« Reply #1 on: October 09, 2018, 01:33:16 PM »
I am not an expert on this, but I think it should work.  I think GM may have had a different tach for HEI vs points, but it seems like unitized ignition and HEI are very close to the same thing.  Since you have multiple cars, I might run a wire over to another one, and a common ground, and see if the tach works for a different car that doesn't have HEI, if you have one.

When we were parting out cars I tested all tachs on an F-150.  I wired it for Trans Am tachs under the hood.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
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1sgtretired

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Re: tach question
« Reply #2 on: October 10, 2018, 01:05:58 PM »
Interesting I do have a couple cars I could try that with.
Thanks
USAF 1st Sgt Retired

1970 RAM AIR III TA. White
1972 455 HO, Blue
1973 Formula, Functional Ram Air set up
1973 455 TA, Red
1976 400 TA sold
1978 Black W-72 TA
2006 Chevy 2500 HD Turbo Diesel
2011 3500 Chevy Turbo Diesel
2012 BMW X5

Re: tach question
« Reply #2 on: October 10, 2018, 01:05:58 PM »
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