Tach calibration - The 1947 - Present Chevrolet & GMC Truck Message Board Network

greenhorn male · 04-30-2005, 01:25 PM

I tested 2 tachs (used, in a cluster) using jumper wires and alligator clips. With light guage wires I could barely get them to work. So I switched to heavy guaged jumpers. One tach (marked 8 cyl) registered 1K, the other one (no visible markings) registerd 800, the sears tach/dwell meter registerd 750. These were taken at idle with one vacuum port open (to air cleaner). The strange thing is both tachs seem to top out about 2200 rpm when I opened the throttle some. I was going to swap one of these clusters in because my temp guage doesn't work in my truck.
Question: Is that a calibration screw in the back? Why does it seem to top out at 2200-2300 RPM? When I install my HEI, what would it do to the readings?

04-30-2005, 01:25 PM	#1
greenhorn male Senior Member Join Date: Jan 2003 Location: Bay Area, Northern California Posts: 1,344	Tach calibration I tested 2 tachs (used, in a cluster) using jumper wires and alligator clips. With light guage wires I could barely get them to work. So I switched to heavy guaged jumpers. One tach (marked 8 cyl) registered 1K, the other one (no visible markings) registerd 800, the sears tach/dwell meter registerd 750. These were taken at idle with one vacuum port open (to air cleaner). The strange thing is both tachs seem to top out about 2200 rpm when I opened the throttle some. I was going to swap one of these clusters in because my temp guage doesn't work in my truck. Question: Is that a calibration screw in the back? Why does it seem to top out at 2200-2300 RPM? When I install my HEI, what would it do to the readings? __________________ 03 Tahoe 72 GMC Super Custom 2500 Custom Camper, my reliable workhorse. Dual gauged tanks, dual battery trays.



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