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589 Posts
I actually counted the idi at 107 teeth but it was dark. mine is pretty close, I have compared it to the edge display. I agree the 58 teeth is bull maybe the powerstroke uses that tooth count. I used a 60 tooth blade and removed six teeth with nine in between each removed. Totaling 54 tooth reading per revolution. as far as accuracy goes the factory tach is about as accurate as the fuel gauge...lol My original concern was that with the six teeth missing, that the needle might bounce erratically or that it was going to throw a code in the transmission controller. It did neither. The tach needle is very steady compared to the speedometer.