<VV> Thank You, now Instruments

[Bruce Schug]

On Nov 5, 2009, at 12:51 AM, Dave Thompson wrote:

> 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.
>
>



Very good post. I agree with everything you said, But...

While I agree with your comments on a cylinder head temperature gauge  
being better than an oil temperature gauge, in that it shows problems  
quicker, 67AC140 uses BOTH gauges.

While a CHT gauge  is quicker to react to temp changes, once the oil  
temp saturates, I want to know how hot it is. It's this temp that  
determines if there's breakdown of the oil. I usually have to drive my  
car about a half-hour at freeway speeds to saturate the oil temp, but  
it does saturate.

When I autocross or even just rev the engine, I want to know how hot  
the oil is. I never rev is (meaning run it over, perhaps, 4.500 rpm)  
or make an autocross run (using a 6,600 rpm rev limiter) until I have  
some heat in my oil. I like to have at least 180 degrees before making  
a run. In cool weather, this may require running the engine at  
2,000-2,500 rpm or so for several minutes while waiting to run.

Yup, voltmeter, CHT (on the Corsa dash) oil pressure, and oil temp and  
you're set. My gauges are Stewart Warner.



Bruce

Bruce W. Schug
Treasurer, Membership Chairman
CORSA South Carolina
CORSA member since 1980
Performance Corvair Group
Stock Corvair Group
VirtualVairs
FastVairs
'67 Monza, "67AC140"
bwschug at charter.net