[RPM427]

I'm not saying the stock tach is off by 1200 rpm all the time, I'm saying when the engine goes to 2000 to 7000 in about .4 seconds, the tach probably just had some inertia and carried through past the 7k mark. But I when I am at the track, the tach seems "lazy" and is clearly not accurate. It just seems slow, the higher your RPM and the faster you accerate the engine (accerating the car or missing a shift), the more inaccurate the stock tack will be. I bracket race an have a hard time shifting at the same RPM because of the stock tach.
Need an Autometer! For the street the stock tack is fine, but if you want to get very consistent track times, you need an aftermarket tach.

Autometer make tachs in a huge selection of sizes, you can make one fit with some patience. Check out thier site:

http://www.autometer.com/hp/index.html