Friday, October 20, 2006

Best use of spare instrument space?

UPDATE: I've decided that I need a combo EGT/CHT emgine monitor, and that I will buy it from someone other than JPI. I did a little research and it didn't take long to find their abysmal reputation for customer support and some of their more heavy-handed legal tactics. I have no patience for that kind of thing, so will look elsewhere for what is in essence a commodity product. It amazes me that a company making a product that is easily available from a competitor at the same price point doesn't realize (or care) what a bad reputation can do to them.

Original post:

Since I moved by mag compass to a new location in the panel, I have an empty 3 1/8" instrument hole to fill. My first thought was to put in a g-meter, but given the type of flying that I do, there's no real need for it.

One need I do have, however, is in the realm of engine management. I do not have any temperature gauges whatsoever, other than oil temp which is nearly a constant anyway.

The two possible engine temp gauges under consideration are either cylinder head temp (CHT) or engine exhaust temp (EGT). My understanding (and please, chime in with a comment if you disagree) is that EGT is more useful in determining the best mixture to set than CHT. Assistance in setting the appropriate mixture is primarily what I'm after, so unless a strong counter argument can be made for monitoring CHT instead, I'm planning on installing an EGT gauge.

Of course, if I were willing to spend the money, I could have both, but graphic engine monitors that display both EGT and CHT are pretty expensive. If I choose to do only EGT, it will be quite a bit cheaper, and I'm not convinced that I need both. Again, chime in if you disagree.

In any event, if I go with EGT, I want it on every cylinder. Leaning based on the EGT of a single cylinder seems pretty risky.

So, with all that said, here is the gauge I'm looking at:

With all four probes, it's going to be nearly $400. A graphical engine monitor that provided both 4 cylinder EGT and CHT is about $1000 more:

I think I will get what I need from the lower cost alternative, but I can still be persuaded.


Another option:

I'll have to measure, but I think I have the required space behind the panel for it to fit. But at $2300 for the display and probes, it definitely blows the budget all to heck.

I looked at the JPI and EI units, but they are all 2-1/4" units, and I'd really like to completely fill the 3-1/8" hole. I'm not ruling out one of the smaller units, though, as I imagine I'd get used to it pretty quickly.


  1. Pretty much anything is an improvement over what you've got, but I think you'll probably regret not going for either the GEM or the JPI engine monitor. The automation help for locating the peaks, etc. is priceless in my estimation.


  2. it's a thing of beauty


  3. You'll get no argument from me there - it is indeed quite a nice bit of kit. Still, it's just too much dinero for what I need it for. If I was building, I think I could make a strong economic case for it, but with the situation being what it is I think I'm going to go for the mechanical quad-EGT and save the fancy glass stuff (and $2000) for a future airplane.

  4. May I suggest a combination CHT/EGT analog guage and probes for each cylinder. Wire the probes to a four position selector switch(es) so as to be able to view each cylinder's temperatures.

  5. I thought about that, but wanted to be able to see all of the cylinders at the same time for leaning. Now that I think about it, though, I suppose I'll determine pretty quickly which cylinder peaks first and lean by monitoring that one. But do I really need CHT? Probes are a significant portion of the cost. What can I tell from CHT that I can't tell from EGT? I think I might google around on that and see.

  6. My opinion is the EGT monitors the condition of the mixture and the CHT monitors the flight condition of the engine.

    It is possible to move one probe from cylinder to cylinder between flights (and changes) in order to balance cooling, when that's complete, leave the probe in the hottest cylinder and only monitor it.

  7. I agree with that. I want the CHT more to know how well my overall cooling is working, and I want the EGT to know how well (efficiently) I'm using my fuel.

    I've more or less decided that I'm going to buy a GEM sometime next year in order to have both. So, do I spring the extra $$$s for a fuel totalizer? :-)

  8. I find that the totalizer is much more useful than my EI fuel gages. The totalizer is very accurate and in combination with a GPS allows me to monitor fuel reserves at my destination by using the time-to-empty and time-to-destination features. It also allows me to repeatably set the mixture for various power settings.
    I highly recommend the totalizer if it fits in the budget.