I know it has been posted that the stock tach's are pretty bad for accuracy. Well my S-AFC II reads just under 7400rpms at the 8k reading of the stock tach. Is it ok to trust the AFC or should I trust the stock tach?

 

There's nothing wrong with the stock tach. Even though both the AFC and the stock tach show different numbers, they are both accurate. AFC has a digital "lag" that makes it show different numbers.

 

hrmm.. good to know i was wondering the same thing.. only im a pretty wussy driver, i would prolly go with the lower reading just to be safe.. lol.

 

So you would follow the stock tacho's reading right?

 

i do, and its easier to read also.

 

what about when what your reading exceeds the stock tach ???

 

that means your having a **** load of fun!

 

i know this is off topic, but what mods are done to get u to rev higher than stock redline??? jw casue i like the idea of staying in one gear longer sence i will be auto xing and drifting a lot it would be easyer and faster if i stayed in one gear instead of upshifting and then down shifting right away

 

Well, between my stock tach and my S-AFR, I see a constant 200RPM difference above ~2k RPM. This difference was evident on the dyno too, it turns out my S-AFR is right on the money.

I drive with the stock tach, but now shift earlier to compensate.

 

i see roughly a 200RPM difference. I follow the SAFC since that is what the ECU sees.

Does anyone know if you calibrate the stock tach?

 

Aftermarket tachs are always off compared to the stocker...I tend to believe that the 15 year old stock mass produced tach is less accurate than the new digital modern technology. I've seen this with haltechs, safcs, monster tachs, etc. All of them cannot be wrong, so the stocker must be.

 

the stock tach is garbage..

if I shift at ~7500RPM, the S-AFC will record peak rpms as hitting 7000-7100, depending on if I have the headlights on or not. The stock tach seems to read higher if there is more electrical load on the system.

it even reads ~150RPM off at idle! s-afc says 550RPM, stock tach shows 700...

 

*shrug* At least my tach is always pretty accurate...

 

I know that there are two pot's on the stock tach. I'm sure one's for calibration and the other one is for the redline buzzer. I'm just not sure which is which. The most likley reason stock tach's differ so much is that they use old electrolytic capacitors, which have a wide tolorence to begin with, and degrade much more rapidly than other discrete components. Besides that, if you look at the FSM; for 7,000 RPM, the allowable reading for the tach is 6,965 to 7,455. Unfortunately, there's nothing on calibrating the tach in the FSM.