Tachmeter input signal??
Thread Starter
Melting Slicks
Joined: Nov 2005
Posts: 3,323
Likes: 142
From: Green Valley Arizona
Tachmeter input signal??
Is the Tach signal coming from an HEI distributor a series of 12 volt pulses?
If so, is the frequency equal to the RPM or half the RPM as the camshaft rotates at half the crankshaft?
Reason I am asking is that the tachmeter I have that attaches to the Tach terminal and frame ground always reads alot lower RPM than the dash tach and I am wondering if it just needs to be calibrated.
Think I will bring an O'scope home from work this weekend and check this out.
But any insight from anyone would be appreciated it.
LannyL81
If so, is the frequency equal to the RPM or half the RPM as the camshaft rotates at half the crankshaft?
Reason I am asking is that the tachmeter I have that attaches to the Tach terminal and frame ground always reads alot lower RPM than the dash tach and I am wondering if it just needs to be calibrated.
Think I will bring an O'scope home from work this weekend and check this out.
But any insight from anyone would be appreciated it.
LannyL81
Burning Brakes
Joined: Jan 2006
Posts: 1,223
Likes: 174
From: Fort Wayne IN
The tach terminal should get a pulse every time the coil fires, so you are going to see a square wave of 4 pulses per revolution. There is a switch/jumper/something in most aftermarket tachs to set it up for an 8, 6, or 4 cylinder engine.
