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  #11  
Old 04-17-2021, 10:19 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by RhinoDrvr View Post
All,

The PMAG’s are timed 1.4 degrees before TDC which equates to a base timing of 23.6 degrees BTDC vice Lycoming’s recommended 25 degrees.
.
What drives you to that conclusion? You said you moved one full tooth from the TDC line. By my math, that is ~2.5 degrees (149/360) or 3* if you have a 122 tooth gear. If you didn't accurately measure it, it could easily be 3 degrees retarded.

I also agree that 1550 if fine though with the oil coking issue in Lyc exh valve guides I do believe that lower is better. Anyghing that keeps the oil in the guides from reaching the oil's oxidation temp is a good thing.
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Last edited by lr172 : 04-17-2021 at 10:27 AM.
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  #12  
Old 04-17-2021, 12:19 PM
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Walt Walt is offline
 
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Sounds high to me, I typically run around 1350 ish, 1450 or a bit less is close to my peak.
I generally run ROP for best power, 20deg fixed timing on my 370 with HC 9.6.

1550-1600 seems rather high, the exh valve is going to be getting hot. Not a great combo if CHT's are up at 400.
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  #13  
Old 04-17-2021, 02:01 PM
RhinoDrvr RhinoDrvr is offline
 
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Location: Lemoore (Fresno), CA
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Quote:
Originally Posted by lr172 View Post
What drives you to that conclusion? You said you moved one full tooth from the TDC line. By my math, that is ~2.5 degrees (149/360) or 3* if you have a 122 tooth gear. If you didn't accurately measure it, it could easily be 3 degrees retarded.

I also agree that 1550 if fine though with the oil coking issue in Lyc exh valve guides I do believe that lower is better. Anyghing that keeps the oil in the guides from reaching the oil's oxidation temp is a good thing.
You are 100% correct. I have a 149 tooth ring gear, so 2.5 degrees is the number I was referencing. My recollection was incorrect.

I did just move away from the Devilís armpit (Mojave desert) to a more temperate climate, so I could retime the PMAGís at peak and see how that changes things. That said; I still donít like the full 37 degrees of advance that they provide timed that way.
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  #14  
Old 04-17-2021, 02:04 PM
RhinoDrvr RhinoDrvr is offline
 
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Quote:
Originally Posted by Walt View Post
Sounds high to me, I typically run around 1350 ish, 1450 or a bit less is close to my peak.
I generally run ROP for best power, 20deg fixed timing on my 370 with HC 9.6.

1550-1600 seems rather high, the exh valve is going to be getting hot. Not a great combo if CHT's are up at 400.
Thanks for the reply Walt. Up at altitude, I see the same. About 1400 is my cruise EGT, which is about 50 degrees LOP. CHTís are no problem (330-360. 380 in a Vy climb). Itís just down low where the PMAGs are a little retarded from 25 degrees that the LOP EGTís climb up to 1500.
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  #15  
Old 04-17-2021, 02:42 PM
sailvi767 sailvi767 is offline
 
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Just curious, have you measured the distance of your probes from the engine?
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  #16  
Old 04-17-2021, 02:57 PM
RhinoDrvr RhinoDrvr is offline
 
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Originally Posted by sailvi767 View Post
Just curious, have you measured the distance of your probes from the engine?
I havenít. Never really cared about my EGTís until I saw them above 1500
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  #17  
Old 04-18-2021, 02:01 AM
KayS KayS is offline
 
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quote: Just curious, have you measured the distance of your probes from the engine?

Quote:
Originally Posted by RhinoDrvr View Post
I haven’t. Never really cared about my EGT’s until I saw them above 1500
that's wat i wanted to express in my first post... your absolute EGT numbers are somewhat meaningless. that applies if you run your LOP procedures and it also applies if you're about to compare these numbers with others. that's the reason why some old fashioned EGT gauges didn't even show real numbers.

if you see somebody else EGT's running 200 F or so lower, that doesn't mean anything as you don't know how different are these probes installed on the exhaust.

well, if your EGT's change because of altered ignition timing... that's a complete seperate topic.

Last edited by KayS : 04-18-2021 at 02:05 AM.
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  #18  
Old 04-18-2021, 07:43 PM
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DanH DanH is offline
 
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FWIW, quick experiment today...set 2400, throttled for 65% at 3000 ft, leaned to peak EGT. Shutting down one ignition was all it took to push EGT from roughly 1450 to 1550.

Someone with SDS ignition could easily dial 2.5 less degrees in flight and see how much it changes EGT
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Last edited by DanH : 04-19-2021 at 05:47 AM.
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  #19  
Old 04-19-2021, 11:30 AM
RhinoDrvr RhinoDrvr is offline
 
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At my next oil change Iíll likely time my PMAGís 1/2 tooth aft of TDC, and see what effect that has. Currently I can climb at Vy of 90 kts to 10,000í on a 70 degree day and keep the hottest CHT at 395. Which is nice, but likely unnecessarily cool. If I can take back 1.5 degrees of timing and keep CHTís under 400 with a 120kt climb that would suit me fine as well.
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  #20  
Old 04-19-2021, 09:35 PM
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skylor skylor is offline
 
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Default Inflight (P) Mag Check

Hi Evan,

On my angle valve (mags), 2 or 3 degrees change in timing does not cause that much change in EGT. Also, unless your probes are literally right at the exhaust flanges, 1550 EGT seems pretty high to me. Have you tried doing an in-flight (P)Mag check when in your low altitude high EGT operational mode to ensure both PMag's are functioning? As Dan stated, the loss of 1 ignition system will create a pretty large increase in EGT's.

Skylor
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