My best happened when I was about 19....my car is a 4-speed and I didn't have a rev limiter so I bought a Mallory tach with built in rev limiter (had a knob you twist to set the rpm at which it cuts out the motor)...I installed it and drove it on the street for a few weeks and one day as I'm cruising down the highway I look at the tach and it's reading double what it should be ....after about 1 mile it goes back to reading normal and doesn't act up again....

So, about a month later I decide to take my car to the track and run it for the first time with my fairly new 438" 383....On my first pass I stage, bring the motor up to about 3K, dump the clutch and it goes about 5 feet and the engine starts cutting out and the whole car starts shaking like crazy!!! Rearview mirror is bouncing around....glovebox opens...I look at the tach and it shows 6K but I know the motor isn't that high....I remember that day when it read double and so I reach up and crank the knob all the way to the right to raise the rpm limit so it'll stop cutting out and I finish the run with a mid 13 second pass....

Imagine being WOT with a stick car, clutch pedal out and against the chip at 3,000rpm....I was freaked out!!!!!

When I got home I pulled the tach off the car and threw it in the trash and haven't had a tach in a car ever since....