Hottest running cylinder?
 

Greetings,
I'm putting a freshly overhauled O-360(180 hp) in my -7A but due to budgetary constraints I can't quite swing a full bore EIS yet so I'm going with Van's single EGT and CHT instruments. Is anyone aware of a particular cylinder traditionally running hotter than the remaining three? If it matters the engine is an -A4M from an Archer. Thanx for any help

--hawk

The number is
 

Cylinder Three for CHT, (right rear)

Airflow under cowl and baffles affects the CHT, therefore #3. I would suggest you consider during flight test you try to move the CHT probe to other cylinders. The CHT is position dependant and I am 98% sure #3 will be your most critical or hottest CHT. However EGT (mixture) affects CHT. The 2nd hottest cylinder is often #2. Cylinder #1 is almost always over cooled and that is why you see large plates on the front of the #1 cylinders. This is why during flight test 4 channels is good in tuning your baffles. How much does a Lycoming cost? I would get all 4 channels (cylinders) instrumented.

For EGT, a good guess is go with #2 or #3 for EGT but no guarantee. The hottest EGT (leanest) can be any cylinder and varies with throttle wide open or partial. If it was me I would go to #2, since some claim that is the leanest at WOT at altitude (below 75% power). If you want to lean with partial throttle, #3 would be my second choice (from what I hear on carb engines). Also cyl #3 is an eaiser EGT installation. However be warned, some say #3 or #4 is always the leanest? Again no guarantee. Again during flight test you could move the EGT probe, but you will have extra holes in those pipes. How much would 3 more EGT probes and a switch cost? Every engine is different and no cylinder is sure to have the highest EGT all the time. (Note buy the PROBES that will work with your future engine monitor if that is the plan).

Plenty of planes have flown with NO CHT or EGT at all. It is not a required gauge. CHT is the most important and you can feel pretty good about #3 being the hottest CHT. Leaning using a single EGT gauge can be done, but you should to do some flight test to figure out how to figure your leanest cylinder if you want to use the gauge for actually leaning. Cylinders #2 and #3 seem to be the front runner for leanest cylinders. Going with #3 for both CHT and EGT might make sense.

EGT is a bit of a guess since it is a function of mixture distribution. You have a carb. Any cylinder could be the leanest. Since an EGT gauge is not necessary to lean the engine (by Lycoming), a single EGT gauge is a just a warm fuzzy, unless you absolutely know that you instrumented the leanest cylinder. Lycoming calls for you to lean (only when at or below 75% power) just to roughness and enrichen for smooth operation. THAT IS IT, NO GAUGE. You can use your EGT gage to watch the EGT raise. Watch to see if it peaks and drops before the engine gets rough. Enrichen just to get smooth operations and note the change in EGT on your gage.

With a single EGT on the cylinder you know is on the leanest, Lycoming says lean to peak and enrichen 100F. A single EGT is better than nothing, but not knowing it is on the leanest cylinder, it can only be used as a suggestion to manual leaning (roughness method). With the cost of gas a 4 channel EGT might save you some money with reduced fuel burn. G

Agree with George that #3 is generally the hottest.

However, consider the poor mans multi-channel CHT (or EGT.) For about $150, you could have 3 more sensors and a 4 position rotary switch to display all 4 cylinders (one at a time, of course.)

Jeff Point
RV-6
Milwaukee

And we all know eveything Lycoming says is true right? Save your beans and get a EDM 700.

Thanx for the replies
 

The EDM-700 is a JPI product, right? Fits in a 2-1/4" hole? Maybe I'll be able to spring for it after I sell my C172 to free up the hanger for the RV.

--hawk

Jpi 700
 

Yes......and it is about 1200. well worth the price! for the peace of mind!
Bob Martin
RV-6....with JPI 700 :-)

Helping You Spend Your Money
 

I've have a JPI-700 in a 172, and put a EI UBG-16 into the RV-7. After 2000 hours flying behind one, I feel naked and ignorant without a GEM on board. Don't waste your money on a single probe instrument, and the rotary switch thing requires a steel trap memory to compare one indication with another. The JPI unit also displays volts, oil and outside air temp by adding probes, so can save the money that otherwise would be spent on separate gauges. The EI can also, but you have to add a pricey interface module for volts.

I'd sure scrimp elsewhere to be able to install a GEM from the get-go. They will teach more more about running YOUR engine than anything else aboard, particularly in the important matter of avoiding high CHTs.

#3 was the hottest on my -7 until I installed a new #2 which remains the hottest by only a very few degrees F. Archives I once searched all pointed to #3 as likely hottest CHT.

John Siebold

Well if you are going to engine monitor
 

Go with A Grand Rapids Tech (GRT) EIS-4000.

For less than $900 you get: http://www.grtavionics.com/model_4000&6000.htm

Spruce has it for $843:
http://www.aircraftspruce.com/catalog/inpages/eis8.php
http://www.aircraftspruce.com/pdf/catalog/Cat06392.pdf

It is by far the best bargain on the market, been around a long time, GRT is known for great support, has 4XEGT/CHT with lean set point pages, shock cooling alert and will warn you if any parrameter limit is exceeded (Hi or Lo).

The basic system comes with All 4 EGT's & CHT's, Tach, Oil Pressure, Oil Temp and Volts. Plus it has flight and total engine hour timers.

With this basic unit you can add these popular options with the purchase of the probe sensor:

Manifold pressure
Fuel levels L&R
Fuel Pressure
Fuel Flow
Carb T
Amps

All the possible standard and optional functioins are :
Standard:
4 or 6 Exhaust Gas Temperatures
4 or 6 Cylinder Head Temperatures
Tachometer
Oil Temperature
Oil Pressure
Volts
Hour meter
Flight Timer with Interval Timer (switch tanks)

Other inputs (with dedicated channels):
Outside Air Temperature
Carburetor Temperature
Vertical speed (VSI)
AirSpeed (AS)

6 Auxiliary Inputs user configurable can provide:
Manifold Pressure (normally aspirated or turbo)
Fuel Pressure
Fuel Level (using capacitive or float-type sending units)
Coolant Pressure
Amp meter
Ignition Advance, second voltmeter, rotor rpm, etc.


For less than $900 you can start with the basic instrument. If you subtract the all the other gauges that you will not need (OP, OT, Fuel Levels, Tach, Manifold, Hobbs meter, Volt, amp) you will save money. If you already bought gauges? Sell them on eBay. You cut holes in the panel already? Well cut them out and put in sub panels or buy a new panel. Even if you got a few optional senders (MAP, Fuel Pressure) it will be about $1,000. IF you have fuel tank senders you don't need gauges, because the EIS-4000 will monitor it for you and warn you of low level! IF you go all EIS-4000 you will save money of seperate gauges and save panel space.

G

But the GRT's interface looks terrible compared to the slightly more expensive ($300 more) JPI. And the JPI fit's in a standard 2 1/4 hole, vs. the propritary hole you'll need for the GRT.

Maybe, but GRT never tried to put Matt Dralle (Matronics, the original RV-List) out of business. Many old timers won't touch JPI to this day.

On a serious note, since I'm the one who suggested the rotary switch setup- that is only if you are really on a budget. I agree with the others who recommend the EIS4000. True the display is not so pretty, but it is very functional and easy to get used to. You could buy three of them for the next lowest price graphic engine monitor. I love mine, and so do hundreds if not thousands of others.

Jeff Point
RV-6 w/ EIS4000
Milwaukee