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Is the OEM tach about as accurate as the OEM boost guage? For anyone who has added an aftermarket tach, or similar item that measures RPM's did you compare the readouts to the tach? The reason I ask this is that I was using the website with the rpm vs. mph calculator to see if I can verify speedo error vs. actual. I know that my speedo has about a ~2 mph error on the high side (I love checking these things with those unmanned radars that flash your speed). When I used the calculator to see what my real speed should be at 3,000 rpm (ignoring other variables at this point) it says I should be doing 80mph - but in the car I'm reading about 75 mph. If anything since my speedo is reporting higher than actual, I would expect to see it to show about 82 mph assuming the calculator is reasonably accurate. So the question that I'm trying to resolve is whether the tach is not as accuarate as we would expect it to be. Since it's relying on the electric signal from the crank angle sensor (I think) - one could conclude that the tach should be failry accurate (maybe within +/- 5%). There are be other factors that influence the RPM vs. MPH calculator results (actual tire circumference, possible clutch slippage, etc....) but I thought the question about tach accuracy was worth asking anyway. Any thoughts or comments on from actual experiences? Dave
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