mrvette
Phantom of the Opera
anyone ever wonder if your tachs are accurate....know how to test it??
something I got curious about so decided to prove the point....
I happen to have a digital audio oscillator goes from damn nearly DC to very fast on the output....
nothing for a Tektronics scope though...got one of them too....
so I decided one day to find out if my tach was accurate or not...since it IS an old OEM POS from a 75-77 vette.....
how to know?? easy...figger 600 rpm idle....that ten trips up and down per second for a piston....damnit, that fast....
5 sparks per second being a 4 cycle engine...duh.....
times 8 cylinders means the sparks are flying at 40 hz....not too fast by electronic standards.....
so to take a old horizontal output transistor from a color TV set, and just clip it to the tach output terminal on my HEI....fire the base lead (transistor input) with the oscillator.... and read the tach...with the ignition on but engine still.....
I can run that puppy from 40 hz which is 600 rpm as above...to 4000 hz which is 6000 rpm, and of course anything in between....
proving the time base is easy with the scope that way I KNOW it's dead nutz on accurate....
I found my tach high at anything above 3000 rpm same 300 rpm all acrocc to 6 grand....slightly high....at 1500 rpm it's dead nutz on....
at idle it's slightly lo....maybe 50 rpm...
just so you know....
I know, I"M bored....
something I got curious about so decided to prove the point....
I happen to have a digital audio oscillator goes from damn nearly DC to very fast on the output....
nothing for a Tektronics scope though...got one of them too....
so I decided one day to find out if my tach was accurate or not...since it IS an old OEM POS from a 75-77 vette.....
how to know?? easy...figger 600 rpm idle....that ten trips up and down per second for a piston....damnit, that fast....
5 sparks per second being a 4 cycle engine...duh.....
times 8 cylinders means the sparks are flying at 40 hz....not too fast by electronic standards.....
so to take a old horizontal output transistor from a color TV set, and just clip it to the tach output terminal on my HEI....fire the base lead (transistor input) with the oscillator.... and read the tach...with the ignition on but engine still.....
I can run that puppy from 40 hz which is 600 rpm as above...to 4000 hz which is 6000 rpm, and of course anything in between....
proving the time base is easy with the scope that way I KNOW it's dead nutz on accurate....
I found my tach high at anything above 3000 rpm same 300 rpm all acrocc to 6 grand....slightly high....at 1500 rpm it's dead nutz on....
at idle it's slightly lo....maybe 50 rpm...
just so you know....
I know, I"M bored....