Testing Tach
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
Testing Tach
Does any one know if the tach signal generator that willcox sells will test a tach that is installed in the vette. Also would it test aftermarket tachs for accuracy. Dave
Race Director
Joined: Sep 1999
Posts: 11,358
Likes: 379
From: Plano TX
Answers are in the product text at the willcox site????
This signal generator will allow you to either bench or car test your tachometer.
Test your tachometer on any GM car from 1975-1991 that uses a distributor signal for operation.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Being an old ET, I have a slight advantage in that I took a digital audio oscillator, and Tektronics scope to my HEI, too that tach wire to a power transistor, drive the transistor with the oscillator, and monitor with the scope, I found the tach was accurate at idle, and at 2500 rpm, but when at 3000 rpm it was optimistic by 10% signal was really 2700 or close.....at 4500 indicated, it was only 4000 in reality....
by 6000 rpm it was optimistic by some 650 rpm....10% off....
so yes, factory tachs are not accurate, same as the speedometers....
by 6000 rpm it was optimistic by some 650 rpm....10% off....
so yes, factory tachs are not accurate, same as the speedometers....
Race Director
Joined: Sep 1999
Posts: 11,358
Likes: 379
From: Plano TX
I'm also particular about accurate gauges. I have the willcox tach board and it has a calibration pot on it (factory board is non adjustable). I built a signal generator and monitored the output on my scopemeter (remember that one, Gene?).
I was able to get an accurate sweep all across the scale by needle position & trim pot adjustments.
For the speedo, I compared it to the reading on my GPS. I found it to be 8% high, so I adjusted it to where now it reads 1-2 mph high.
I was able to get an accurate sweep all across the scale by needle position & trim pot adjustments.
For the speedo, I compared it to the reading on my GPS. I found it to be 8% high, so I adjusted it to where now it reads 1-2 mph high.
