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35 OLDS,I'm wiring my streetrod with a painless system,using autometer gages.I'm using an HEI distributer. Is a tach filter nescessary to prevent damage from high output ignition ? It is not mentioned in any instruction manuel that came with wiring or gages , but I've run across this in an older electrical manuel. Also,my NAPA parts guy claims that .035 gap is correct to use on my R45 spark plugs.I've read here to use .045 when using HEI. He claims that G.M. used to use a larger gap with the HEI but went back to the smaller gap. Any comments on this would be appreciated.Thanks guys, 35OLDS
 

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Doc here, :pimp:

Tach filters were used with Stock GM Tach's and HEI Dizzys , years ago to prevent damage to the Calibration Boards..(Circa 80's)..

Some MSD's require a Tach filter IIRC, IF , the tach reports in error. Usually, they include that in the Installation sheet and a part number If the problem is suspected.

In general, and for the most part, you Should not need the filter.

Doc :pimp:
 
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