I think a turbo tach is the key to success whether you just
want to use the stock 2nd gen turbo as is, want to modify
it or replace it with a TO4. If you want replace it with a TO4
get ready for big expenses and lots of time.
My guess is well over $1500. I know many people that have
complete engines for the same amount of money. Others
consider it peanuts :)

OK here is a cheap device by comparison.

I at first thought I could find something off the shelf
from Keyence but I called them and the fastest thing they had
was 33 usec. http://www.keyence.com/usa.php

Not fast enough. I figure 100,000 RPM 1666 RPS
or one rev every 6 to the minus 4 seconds or 00.0006 which looks
like 6 usec if my memory and arithmetic are correct.

Perkin Elmer has a .5 nano second photo diode that will do the job.

http://optoelectronics.perkinelmer.com/catalog/Category.aspx?CategoryName=Photodiodes

Download the Emitters and Detectors Brochure pdf.

All we need now are; fiber optics, an emitter, an amp and a counter.

If somebody knows of an off the shelf solution I would love
to hear about it.

We can also use this turbo tach when it comes time to test
the turbo compound engine on the Mazdatrix dyno.

Paul Lamar ...No rotor no motor.