I was checking some aftermarket gauges for my '91 NA S5 FC on eBay, these ones to be exact:

http://cgi.ebay.com/ebaymotors/ws/eB...4078900&rd=1,1

http://cgi.ebay.com/ebaymotors/MAZDA...QQcmdZViewItem

-- and I noticed that all NA S5 gauges have a 8k RPM redline... after checking my own tachometer (remember, also a NA S5), I noticed mine had a 7k RPM redline.

By chance, I came across a Turbo S5 gauge:

http://cgi.ebay.com/ebaymotors/89-91...QQcmdZViewItem

... Turbos have a 7k RPM redline?

So... NA's have a 8k redline, while Turbos have a 7k redline...

But... why does my NA have a 7k RPM redline!?

 

My S5 NA does have an 8k redline, maybe a previous owner of your car changed the tach and ordered the wrong part?