Re: The Red Mark

[Andrew Duane USG/PE <duane@zk3.dec.com>]

Hairy green toads from Mars made Alex Kowalski say:

> I have a question.  What is the accuracy of Audi tachometers?  
> Anybody ever heard of them been off severely?  Given that some 
> speedometers I've owned and driven are off by five percent or more, I was 
> wondering about the tachs...  if the tachometer was off by 10% 
> (admittedly a large amount), you could be doing damage to the engine by 
> revving it to the redline.

Different problem.

The speedometer reads wheel revolutions, and reports the "speed" based
on it's assumption about nominal tire circumference. The true circumference
changes a lot based on tire pressure, tread wear, actual size, nominal
size, etc. It is not uncommon for tires to be off by more than 5-10%.
Thus, the speedometer is off by more than 5-10% even though it is
reading perfectly.

The tach on the other hand directly reads the engine speed with an
electronic pulse. No assumptions about crankshaft size or stroke length.


> P.S. there are always those who ignore the tachometer anyway and shift by 
> elapsed time from the end of the driveway ;-).

Got a problem with that?

-- 

Andrew L. Duane (JOT-7)			duane@zk3.dec.com
Digital Equipment Corporation		(603)-881-1294
110 Spit Brook Road
M/S ZKO3-3/U14
Nashua, NH    03062-2698

Only my cat shares my opinions, and she's too heavy to care.