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EGT probe locations for 912S with Zenith exhaust?

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jf3sb

Joined: 02 Dec 2007
Posts: 20
Location: Olathe, KS

Posted: Fri Mar 05, 2010 3:41 pm Post subject: EGT probe locations for 912S with Zenith exhaust?

Here's a question that I see has come up a couple times before in the archives but without answers, so I'll try again...



I want to mount a couple of Dynon's "hose-clamp" style EGT probes on the headers of the back two cylinders on a 912S on my 701 project with Zenith-furnished exhaust system.  The Rotax installation manual calls for them to be placed 70mm behind the header socket flange, but placing them there puts them on a curved part of the header.   Anybody on the list been down this road before and have any recommendations?



Also any opinions from the folks who are flying on how useful EGT monitoring is on this engine?  I like the idea of having EGT data, but am not particularly keen on inviting exhaust leaks to get it unless it serves a purpose.



John

CH701

Olathe, KS

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n752ms(at)softcom.net
Guest

Posted: Fri Mar 05, 2010 6:54 pm Post subject: EGT probe locations for 912S with Zenith exhaust?

John.



I have four EGT probes on my 912ULS.  All are of the hose clamp type.  I 

have 80 hours on them and am doing my annual inspection this week and don't 

see any leaking around the clamp.



EGT on a Rotax 912 is information only.  You don't have a mixture control on 

a Rotax, so there is nothing you can do to change the EGT temp.  You could 

pull the carb apart and change the needle setting if it was always lean or 

rich, but Rotax has it pretty well dialed in from the factory.  It will tell 

you if you have a vacuum leak or some other problem on one side and not the 

other.



The back two cylinders run about 150 degrees hotter than the front two. 

Same with the CHT, back runs hotter than front.



Mark S.

701/912ULS



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jf3sb

Joined: 02 Dec 2007
Posts: 20
Location: Olathe, KS

Posted: Sun Mar 07, 2010 6:18 am Post subject: Re: EGT probe locations for 912S with Zenith exhaust?

Sounds like you've got a good working installation that the rest of us strap-hangers can copy, Mark.   Did you mount the probes at the Rotax's specified distance (even if on a curved part of the header), or move them downstream to a straight spot?



Thanks...



John

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n752ms(at)softcom.net
Guest

Posted: Sun Mar 07, 2010 8:39 am Post subject: EGT probe locations for 912S with Zenith exhaust?

John.



I tried to use the specified distance.  It seems simple enough until you 

start to measure on the curve.  Do I measure the ID of the tube bend  or the 

OD of the tube bend?  I chose to drill the hole so the tip of the probe came 

out 70mm down the center line of the bend from the exhaust flange.



I also use CHT probes, located at the Rotax recommended place.  Even though 

that isn't a true CHT, because the probe is in a water jacket.  Some combo 

of water temp and CHT I guess.  But that is what they use for the max CHT 

measurement location.  I also installed a water temp probe located in the 

water line as it leaves the top of the cylinders, the hottest point.



Mark S.

701/912ULS

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Geoff Heap

Joined: 12 Jan 2006
Posts: 266
Location: Lindenwold, New Jersey

Posted: Tue Mar 23, 2010 4:04 am Post subject: Re: EGT probe locations for 912S with Zenith exhaust?

John. I just drilled mine (912UL) as per the Dynon installation manual. They suggest 2" to 8" from the cylinder. This works out nice as 6" comes at a very nice straight stretch on the two rear headers. Sorry my input came a little late. Did you resolve it and drill them yet. I also bought some header wrap for these areas only, to protect the cooling hoses that pass so close by........Geoff

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jf3sb

Joined: 02 Dec 2007
Posts: 20
Location: Olathe, KS

Posted: Sat Apr 03, 2010 6:42 am Post subject: Re: EGT probe locations for 912S with Zenith exhaust?

Thanks for all the feedback.  The question is resolved and I'm now on to over-analyzing the next issue.



Per Mark's suggestion, I mounted them at the Rotax-specified distance even though it put the probes on a curve.  The "hose-clamps" fit fine without deformation and I'm no longer concerned about leaks or loosening.



I suspect the header wrap is a good idea too for the reason Geoff mentions.  I've got some but I think I'll do some full power runups before I put it on so I can get some before and after EGT data.



They don't call it "Experimental" for nuthin...



John

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