Garmin EIS with Merlyn Black Magic?

[hubcap]

Is anyone here using the Garmin EIS and G3X in an installation along with the Merlyn Black Magic upper deck pressure controller? I was told that there could be an issue with the manifold pressure reading interfacing from the Merlyn and the Garmin EIS. I am not THAT technical so I was curious if anyone else had encountered any issues. I am currently running with a JPI 900 with the Merlyn Black Magic.

[PeteMc]

By no means an engine guru here.  But in what world would there be "interference" because of the Black Magic?  Doesn't the Manifold Pressure reading just come from what the MP is??  I've never seen any strange readings with my stock MP gauge in my K.

Now it did get my attention when I put in a digital tach and the single digits were bouncing around.  Totally normal, but you don't see that resolution in the stock analog gauges.  So if the EIS shows that much resolution in the MP reading, some people may see that normal fluctuation as "interference" just because they've never seen it before.

At some point I'm going to go to an EIS or newer JPI.  It will be interesting to see what others say about this.

 

[hubcap]

It had something to do with the way MP is measured when the Black Magicis installed.

[N201MKTurbo]

I can’t imagine how the Merlyn would affect the readings, but a lot of people also install an intercooler. The intercooler will increase intake air density and requires a lower MP limit. The instrument probably isn’t certified to indicate the lower limit.

[kortopates]

Someone is terribly miss informed!! Absurd!

MP measurement isn’t effected by the Merlin.

[81X]

I just got a G3X installed on my 231 and I have the Merlyn upper deck controller on my engine.  No issues expected or realized in actuality.  
 

The MP sensor measures absolute pressure in the intake manifold and the Merlyn simply allows for the wastegate to vary so it can fully close and allow for a higher turbo critical altitude, and also to help reduce bootstrapping. 
 

Clearly someone knows enough to be dangerous- Merlyn impacts MP to some degree, but not in the manner they are thinking. 

[carusoam]

In some MP sensor applications the pressure can bounce around a bit…

it will depend a lot on where the sensor is located and what is going on upstream of it, and down stream as well….

If the pressure is delivered smoothly…. Like the Merlyn…  there won’t be a lot of vibration waves getting to the sensor…. From upstream.

If the sensor is close to an intake valve… each time the valve opens and closes… the airflow nearby is affected….

To dampen readings caused by vibration type of flow issues…. A device called a snubber is used… in front of the sensor…

With digital instruments the data gets averaged over time to provide smoother usable data…

 

Other issues… could be a weak sensor… or bad connection…

Mooney sensors and instruments and hardware a well engineered to perform together….

If you are not getting the performance you expect… continue to dig deeper…

 

There are a few discussions about OilP snubbers and JPIs around here…

Snubbers are selected around the fluid being measured…

Compare your sensor and location to others….. see what is different…

Got any pics?

PP thoughts only, not a mechanic…

Best regards,

-a-

[jlunseth]

I have a JPI 930 and have zero problems with the MP readout. Perhaps what you are thinking about is a differential temp readout which I think you need under the Turboplus STC, if that is the brand intercooler you have. Others may require it also, I just don’t know about that. You get a chart to be used to mathematically adjust your power setting based on differential temperature. Differential temp is the difference between Compressor Discharge Temp, which is the temp of the air coming out of the turbo, and Induction Air Temperature, which is the temp of the air after the intercooler and as it goes into the induction system. The Turboplus came with a Differential Temp gauge. That differential temp varies depending on altitude, cruise speed etc. At cruise it is around 75-125, in other words, the temp of the induction air is 75-125 dF less than it would be without the intercooler. Many of those old diff temp gauges (it was a strip gauge) have crapped out. My JPI reads both CDT and IAT, and displays a “Diff” so I am legal without the original gauge. Doubt that the Garmin does that. All that said, I have not used the charts or the diff temp gauge in years. My experience was that they substantially overstated the increase in power due to the intercooler, particularly when operating ROP. I use my own settings and they seem to work for me. 

[M20F]

On 8/5/2022 at 11:32 PM, PeteMc said:

By no means an engine guru here.  But in what world would there be "interference" because of the Black Magic? 

I think you answered your own question here.  

[A64Pilot]

Many or most digital instrumentation has software that smooths the reading, Pipers turbine apparently have a “snap” that is when they get close they snap to the correct reading. Pipers engine DER told me that, I’ve not flown one myself. On the MVP-50T if you had a good ear for it you could hear a slight RPM droop when throttle was added, but the MVP readout would stay steady otherwise the constant one or two RPM flickering would be annoying.

[jlunseth]

Well, I suppose its possible there is some kind of interference. The Merlin is a differential pressure controller, meaning it tries to maintain a constant difference between the pressure before and after the throttle. I don't know exactly how it measures this pressure difference or how it is installed, but it makes sense that there would be pressure sensors on each side of the throttle and perhaps that means there would be some mechanical interference in trying to install the sensor for the EIS, say, if it wants to go in the same spot as the Merlin "after throttle" sensor. It is not an outlandish question. But there would seem to be plenty of room to install a sensor after the throttle and the MP after the throttle is what it is.

The Merlin's function is not just to fully close the wastegate and allow higher altitude flying than the fixed wastegate, that is certainly one effect of it but was not the principle purpose. The principle purpose was to stop bootstrapping. The lower deck fan of the turbo is driven by the kinetic force of the exhaust coming from the engine. If the pilot increases the MP, that increases the power output of the engine and also the force exerted by the exhaust gases on the lower deck fan. That causes the lower deck fan to spin faster, which causes the upper deck output to increase, which increases the MP more than the pilot wanted. That increase in MP in turn increases the exhaust output further, so up goes the MP some more. The pilot intervenes and tries to control it by reducing the MP again, and that reduces the exhaust which reduces the turbo output. Thus bootstrapping. The purpose of the Merlin was to even out those changes so that bootstrapping was no longer much of an issue. To do it the Merlin senses differential pressure across the throttle. I doubt that the Merlin reducing bootstrapping would have any effect on the Garmin EIS, but sensor placement might be an issue. Maybe where do two sensors go on the output side of the throttle?

Edited November 29, 2022 by jlunseth