i know the factory tach isnt very accurate in its reading but are they consistently inaccurate? as in if the factory tach reads 1000rpm more or less at say 5000rpm does it always read the same at that rpm? I dont really want to install an aftermarket tach for a sleeper look.

 

It depends on the car, but I don't believe 1,000 rpm is normal. I would say more like a couple hundred.

 

i was just using that as an example. i dont know how much my tach is off by but i want to know if these tachs are off by the same amount every time.

 

no, it varies from car to car.

 

no offense but lets try this again......

in any given car....will the tach be off by the same amount every time you rev the engine in THAT car? get what im saying? i knwo all cars are diff and know that all the variations will be diff but in the same car with the variation be the same every time you accelerate through the gears?

 

The further you rev the engine the further the tach will be off.

 

lets simplify this some more..... the only thing i really care about is the only rpm reading that matters redline/racing shift point (whichever comes first) Will the tach be off the same amount at the engines redline everytime i bring it to redline? what i want to know is will the facotry tach give a repeatable redline rpm even though the displayed RPM is different from the actual.

 

heres how to do what you're asking.

take a scan tool, one that shows RPM.. i used winALDL..

rev the car so that the SCAN TOOL reads your redline RPM.... then look at what the tach reads...



the tach is inaccurate but what is shows is repeatable... it doesnt change everytime you rev it.

 

how much is yours off by?

 

at a real engine speed of 5k it reads 6130 at idle its off by 300.


i have a 91 so its the newer style one.... btw my tach really sucks for some reason... most tachs arnt off that much.

 

damn man, that's a lot!

 

Ha I got ya beat. my stock tach is off by 1000 rpm's at idle, and gets worse the higher up you go. when I actualy rev to 4000 rpm's(aftermarket tach installed) my stock tack pegs past 7000 rpm lol

IMOP it is best to get an aftermarket tach put in.
since I installed my new tach my stock tach has recently started to read about 200rpms higher at all times, and my new tach still reads the same as when installed. so what ever makes the stock tach read so poorly can apparently get worse.