In article , "Mike Noel"
wrote:

I have suspected for a while that my old analog tach was lying to me. My
Archer's static RPM at take-off was measuring about 22k and the minimum
spec
was 2325, but the plane seemed to have good cruise speed. When I pointed
an
optical tach through the windshield I read a static RPM of 23.4K. At
cruise, 25K on the analog tach translated to 25.8K on the digital tach.

Any suggestions for a replacement digital instrument? It would be nice
to
drop it into the old tach's mounting and possibly get a few more
functions
from the same piece of real estate.

originally posted 6 May 2003:

After spending some time troubleshooting an oscillating
tach needle, I decided to put in a digital tach in my cherokee.

There appeared to be two choices, a Horizon Instruments digital
tach, and an Electronic Instruments digital tach. Both are STC'd
for a cherokee 140, but neither STC specifically covered a
cherokee 140 with a 160 hp engine (the RAM Aircraft 160hp STC
requires the tach to be re-marked). I believe that both cost
about the same and both have simple electrical installation.

I decided to install the Electronic Instruments R-1 digital
tach primarily because, after talking with both EI and Horizon,
I thought the 377 approval would be easier with the EI R-1.
It turns out that there was no particular advantage to installing
the R-1 from an approval point-of-view. Getting the FSDO and IA
approval was pretty easy. Approving the P-1000 would not have been
more difficult.

The installation was easy, except that the EI R-1 tach doesn't fit
in the "normal" tach hole. The R-1 tach is deeper than the original
tach and makes contact with the top of the brake handle. As a result,
I had to swap around the GEM 602, digital OAT display, and the tach.
Not hard to do, but still a pain.

Bottomline: The R-1 works fine. But I think the Horizon P-1000
digital tach would probably have been better since, I believe, it
fits in exactly the same hole (at least a couple of other cherokees
didn't have an issue installing it). Also, the P1000 will annunciate
a bad mag, which the R-1 does not.


you can google for the entire thread.

--
Bob Noel