At 04:32 PM 6/4/2002 -0400, Mark Sirota wrote:
>Okay, so supposing the answer is that I do need a new rev limiter, what
>should I buy? I'm amazed by the variety of choices out there.
Mark,
A couple of years ago I changed from the Microdynamics rev limiter to the
basic MSD with the addition of the MSD rev selector switch. Compared to the
Microdynamics, it was a challenge finding a nice dry, not too hot, place to
mount the MSD (I mounted the Microdynamics literally on the roll bar
padding above my left shoulder outside the engine compartment. Since it is
small and black (like the roll bar padding tape) and well sealed it worked
out very well out in the weather, even towing in thunderstorms on an open
trailer.
The MSD has the advantage of being easily adjusted based on how "serious"
you are about the event. The switch can be purchased/setup with the normal
FF rev range. To avoid inadvertent adjustment I cover the switch with a
small cap secured by racer's tape, even though the MSD and switch is
mounted under the engine cover since it is too big and obvious (and maybe
not weather proof) to mount on the roll bar.
The MSD can also drive a shift light.(and NOS if you can figure out where
to hide it)
For MSD, see Summit Racing's catalog and/or web site. I think the Summit
price for the MSD system may be cheaper than the various Pegasus/TrueChoice
prices for their hard to adjust small units but I'm not sure.
I don't know if MSD's electronic ignition with built in rev limiter
complies with our new electronic ignition option since it wasn't part of my
shopping research a few years ago.
I'm sure that the MSD rev limiter draws more current than the Microdynamics
unit. Even the Stack draws about a 1/4 amp so be sure to wire one so the
master switch cuts it off!
Note that any smooth cut rev limiter (in my experience) will exceed the
preset limit if you hold a short gear on the limiter for a second or two.
This was true with the Microdynamics unit with both the Jones mechanical
and the Stack electric tach and with the MSD with the Stack tach. Even with
a rev limiter, the engine can still accelerate in an autocross gear (it is
just causing a major missfire, not cutting fuel in our cases).
With my "safety engineer" approach to reliability and having spent way too
much time reading Carroll Smith's books, I ended up mounting the MSD and
its selector switch on that neat white plastic "rubbing strip" material
that KRC sells and then ty rapping the assembly to available frame stuff
near the right front of the engine under the bodywork. This dampens
vibration and was probably the coolest and dryest place available near the
coil. I would attach a picture . . . but no digital camera:-) Note that I
learned about using ty wraps from Amos Johnson (Team Highball) who was
famous for reliability.
I think there are "mid priced" data acquistion units available now that
would combine the best of a recording tach, GEEZ, and the relatively basic
stuff needed for segment timing. I have avoided shopping to help resist the
temptation but I'm sure that SportsCar and links on SCCA.org can lead you
to sources. Make sure that whatever you get actually will "playback" revs,
not just the highest peak IF you want to have that info available.
I got the Stack tach set up for 10 samples per second vs 20 to maximize
recording time. However, in autocrossing stuff happens to revs faster than
every 10th sometimes so playback can be jumpy. Since playback is like
playing a tape but with the tape always resetting to the beginning of a
series of runs for PLAYBACK of any run, the extra recording time probably
isn't worth it for just autocrossing because it would take to long to get
to the last runs when playing back a bunch of runs. I generally review the
early runs individually for hints for the next run and then erase them.
I'll keep the last run or two for future reference after I get home and
maybe comparison to GEEZ data.
Dick Rasmussen
CM 85
85 Van Diemen FF
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