2 waze to measure speed, cop radar, and GPS, out of the two, I think GPS is more accurate.....I know my speedo is good till 80 witch is really 78mph.....
at 100 mph, it's really only 94 mph.....and so forth......
tach over indicated 10-15% also, proven by driving the HEI with a digital audio osciallator, driving a power transistor, running off the tach out of the HEI.....a cliplead setup, easy do, and tracked by my Tektronics Scope,
tach is from a '75+ shark, in my '72 hotrod.....so it's electronic, not cable....
and it over indicated about 4-800 rpm above 2500 rpm.....worse a higher RPM's of course.....
600 rpm idle is ten revs/second or 5 sparks/second per cylinder....50 sparks/second is really slo for the electronics.....but 6000 rpm for the engine....
