vintage tachometer with LS?

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Mar 9, 2018 | 03:02 PM

GonHuntin

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vintage tachometer with LS?

Doing a swap on a '73 Mustang and would like to keep the factory tach and gauges. I know the speedometer can be converted to electric or a converter used and the gauges shouldn't be a problem.

I have read that the tachometer needs to be set for 4 cylinder but that is not an option with this factory tach, what can be done to make it work???

Mar 9, 2018 | 07:41 PM

Modchevelle

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What pcm? I have a Holley HP and there is a tach output.

Mar 9, 2018 | 07:58 PM

ls1nova71

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From: Liberty, MO

Quote:

Originally Posted by GonHuntin

Find someone with some tuning software, HP Tuners or similar, and have the tach resolution changed from 6 to 3, that will make it work with an 8 cylinder tach. You may need a pull up resistor to make the signal a little stronger for it to work though.

Mar 9, 2018 | 08:05 PM

Michael Yount

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Feed 12V+ through a 1000 ohm resistor into the tach signal line between pcm and tach - that'll convert the 5V tach signal PCM output to a 12V signal the old tach can understand.

So - two things to do - 1) the change mentioned above to change the signal so it's 'counting' correctly for a V8 tach; 2) the change from 5V output to a 12V output.