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View Full Version : How to test a tach?


kah68
07-09-2007, 09:06 AM
My 89' 351 with powerslot and 13.7x17.5 O.J. XMP 454 seems to be over reving by the tach. If I take the throttle to 2/3 it will run well into 44-4600. But if I open it right up to the stop it only goes to 5000. On radar 4500 rpm on the tach is giving 37 mph which seems low to me. I know 4500 is max but I'm not sure I'm getting an accurate reading. How do I test the tach to make sure it's correct?

pilot02
07-09-2007, 09:14 AM
My 89' 351 with powerslot and 13.7x17.5 O.J. XMP 454 seems to be over reving by the tach. If I take the throttle to 2/3 it will run well into 44-4600. But if I open it right up to the stop it only goes to 5000. On radar 4500 rpm on the tach is giving 37 mph which seems low to me. I know 4500 is max but I'm not sure I'm getting an accurate reading. How do I test the tach to make sure it's correct?

Find someone with a dwell meter/tach that you can borrow and compare it's readings to the installed tach.

kah68
07-09-2007, 09:29 AM
I am running a fully electronic DUI ignition, can I use a dwell meter with this type of set up?

pilot02
07-09-2007, 09:47 AM
you won't be able to test the dwell of course since there are no points but you will be able to use the tach function by attaching the RPM pickup to the #1 plug wire.

kah68
07-09-2007, 12:19 PM
http://www.performancedistributors.com/

I have one of these, it has a pick up built right into the cap for the tach wire. I suppose I could test a new tach on the pick up but don't want to buy a new tach if there is nothing wrong with the old one.

K