<VV> Thank You, now Instruments

[Dave Thompson]

<SNIP>
My next mini-projects will be to check out the brakes (probably need new
shoes) and add a set of gauges, oil temp, oil pressure, and amps (under the
dash, I'm not cutting up the dash unless I add A/C, which may happen some
time down the road).  I was never one to trust idiot lights to tell me
what's happening under the engine cover since by the time the light comes
on, it's often too late!

<SNIP>
Bill Hershkowitz 69 Monza 110 PG #5056
<SNIP>

Bill,
For what it's worth,
I have played around with many different gauges in the past. Many
inexpensive gauges are surprisingly inaccurate. Several years ago, a buddy &
I did some comparison tests on several brands of instruments for his flight
Corvair engine on a running stand in his front yard. We hooked up several
oil pressure and volt gauges all at the same time. We also had several oil
temp gauges hooked up to a rotary switch. 

We used two no-name brand, Stewart Warner, Auto Meter and Wasatch.

The no name brands were way off from the name brands. The three name brands
were all within a needle's width of each other. But all were different from
each other. He used Westach for his homebuilt airplane. I intend to someday
install Oil Pressure, and a voltmeter in my Spyder. I will most likely use
Auto Meter for my car (but that's just my opinion).

Our conclusion was that if you want accurate measurements, spend the money
for a good name brand instrument.
As for which instruments to use, I agree with Frank Burkhard. 

A Volt meter is better for electrical system monitoring. An ammeter, unless
wired directly in series with the battery wire will not give you an
indication of what the entire electrical system is doing. In our Corvairs it
is impractical to run two very large wires from the battery to the
instrument and back to the binding post on the frame rail next to the
battery. The wires need to be large to reduce the resistance of the wire
which will throw off the ammeter reading. They DO make a device called a
shunt that allows smaller wires but I've had bad luck with them in the past.

A volt meter, on the other hand can be wired to almost any +12v wire. I
would choose a +12v source that is switched with the key. When the engine is
not running, you should read about +12v. When the engine is running, the
alternator should be charging thus you should read from +13.5v to +14.5v. If
you are drawing a large amount of power from the electrical system, such as
using a large stereo amp, you will see a voltage drop. If you throw a fan
belt, the alternator will stop charging and you will read +12v or lower. If
your voltage regulator goes south on you, the voltmeter could show a variety
of readings except what is normal.

As for oil temp verses Cylinder head temp (CHT), as Frank said, our air
cooled Corvairs will indicate cylinder head temperature change much faster
than oil temp change. Using a CHT will allow you to see temp trends much
more quickly and allow you to take appropriate action before any damage is
done. 

On a side note, Most aftermarket CHT's come with a thermocouple (sender)
that either connects under a bolt on the head or under a spark plug. You
might consider getting two and placing one on each head. Install a small
switch by the CHT instrument and you can use it to monitor both heads. You
can also use it to identify if one carb is leaner/richer than the other. I
recommend that you place the thermocouple near the hottest cylinder of each
head. Some people have used the idiot lamp switch hole on the head to attach
the thermocouple using a bolt of the correct threads.

I recommend that you look for electric gauges rather than mechanical. A
mechanical oil pressure gauge will require you to run a tube all the way
from the engine to the dash board; a great place for oil to leak all over
the underside of your dash. Electrical gauges will allow you to run wires.


These are just my opinions. Take them or leave them.

Dave Thompson
63 Spyder vert
Westminster, CA