Tach and Speedometer accuracy

Sorority Demon · Oct 17th, 2005, 12:40 PM

So I had the SAFC-2 installed in my car last week. I kinda stole the install idea from someone here after seeing a pic of it up where the sunglasses holder is, I think it was brandon. I didnt remove the holder, but rather had it placed in the holder, where I can still flip it up and down to show/hide it. I was suprised as to what it can monitor especially the battery voltage. But what suprised me the most was the inaccuracy of my tach. This was installed in my automatic.

The tach will read about 600rpm when I am in drive at a complete stop. I look up at the Safc and it will read about 660-670. In neutral or park, the tach reads 750, the Safc 810. When the Safc says I am revving at 4000rpm, the tach reads around 4200. When I hit the redline on the tach, the highest reading I have seen on the Safc is just over 5950. I was wondering which one would be the most accurate.

At 100mph, the tach reads 4k, but at about 104mph the Safc reads 4k. Which of those readings is going to be more accurate? Or is the speedo off by enough that no matter what I am revving the speed that I see is going to be wrong? I was not racing, I was just testing the unit. It seems like the higher the rpm, the more innacurate something gets.

I have not adjusted or corrected anything on the safc, I just had it installed to give me the enigne info. I will by dynoing it in a month or so after I get some new cams and the bsr kit.

BlackoutSpecV · Oct 17th, 2005, 03:50 PM

The tach and spedo of the car are never going to be 100% acurate... In fact most spedometers are off by about 5% and closer to 10% the faster you go. This explains why people sometimes see trap speeds lower than they expect...

Assuming the SAFC was installed correctly then I would say that it is likely to be far more acurate than the gauge cluster.