8k rpm ...

12swinger said

Please
My buddy Mark H campaigned a stock bodied Duster with a destroked 340, that I’ll admit wasn’t all that quick, would routinely have the mechanical telltale tach stuck on 11,500-12,000 rpm. He claimed 13,000 but I saw the tach after a pass many times.

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Those tachs were notorious for two things. Inherent inaccuracy and cable whip.

The longer the cable, and the more bends in it, the less accurate it was and the more the cable would whip the needle.

Had a buddy running a mag with a tach like that. I think it was a Moroso but I'm not 100% sure on my recollection on that.

He ran a magneto so he didn't want to swap tachs. And he said he always shifted at 8800 and the tell tale would show that. The issue was nothing added up. His MPH, gear ratio, tire size...it was all wonky numbers.

He finally bought a new Auto Meter tach for a mag that had an inductive pick up and had it checked to make sure it was accurate.

Next thing you know...he is actually shifting at about 7800 and crossing on a good day at 8000.

Which, not coincidentally matched his gear ratio, RPM and MPH.

Many tachs are junk.