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EGTs during climb? Jab 2200A

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EGTs during climb? Jab 2200A

Postby The Red Baron » Wed Oct 24, 2018 7:47 pm

Hi All. I've got a Jab SP470 with a 2200A engine. I've noticed during climb out after take-off and any en-route climb the EGTs read up to 760 C. I know the EGT sensors are optional extras and there doesn't seem to be any limitations for EGT that I can find. But I was wondering if this is a normal level.

Anyone got any comparison?

Thanks in advance.
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Re: EGTs during climb? Jab 2200A

Postby Steevo » Thu Oct 25, 2018 9:09 am

You will find question after question on EGTs. In my experience, very few people actually get them to work exactly as Jabiru say they should do.

Jabiru say that greater than 75% power, EGTs should be between 640 and 680 DegC. Under 75% power they should be between 680 and 720 DegC. But this depends on a lot of things. The location of your EGT sender and even the quality of your EGT sender can make them inaccurate. Also, there is a thing called cold junction compensation that will also affect the readings.

In my experience of playing around with a few Jabiru engines and trying to tune EGTs, I have never got it perfect.

I currently own a J160 and share an SPL450, both with the 2200A engine and on both of them they do not follow the Jabiru pattern despite trying every tuning combination possible. I never get a lower EGT at full power in the climb and I find that the upward pointing nose tends to make the EGTs read higher. Once I level off at full power my EGTs go well within spec but not in a climb.

There is also the spread of the EGTs. I have never got them exactly even. You can tilt the carby to adjust the side to side spread but again on none of the engines I have ever played with have I never managed to get them perfect.

What you are experiencing with your EGTs is exactly what I get on both my engines and the 2 other engines that I have access to. In theory, those values are telling you that you are running too lean at full power. By rights, you should increase the size of the main jet. I have tried this and it made absolutely no difference in the climb.

You could try putting carb heat on during the climb and see if the temperature comes down a bit (that richens the mixture a little).

I have now given up with worrying about EGTs and as long as my EGTs are within specification during straight and level, then I leave it at that. Even with my high EGTs in the climb, I have never found any signs within the engine itself.

I have now come to the conclusion that the nose up either affects the equipment (cold junction compensation), or it is simply just affecting the air/fuel in the carby. It is for such a short time that I have given up investigating it any further.

The EGTs, do seem to work a bit better on the 3300 engine from people I have spoken to.

Personally, if 760 DegC is the highest you are getting on a temporary basis, then I would forget about it, You will just be venturing in to a money pit and loads of wasted time if you try and bring that down and tune it all properly. See what your spark plug colours tell you.
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Re: EGTs during climb? Jab 2200A

Postby PKnight » Sun Oct 28, 2018 6:12 pm

I agree with everything that Steevo has said.

I had an SP470 for 6 years and flew over 550 hours on it. As I didn't have EGT gauges fitted I had no idea what the EGT's were but I kept an eye on the condition of the spark plugs as a check on the ignition being reasonable.

I do have EGT gauges fitted to my J430 and I regard them as giving a rough guide to the condition of the combustion rather than a true measurement. The trouble is that as they give digital read-out small deviations look significant when they are not.
I recently replaced one of the EGT senders and found that the new one was reading 50 deg C higher than its compatriots. Did this indicate a serious fault? Nope. I found that I had not put the sensor far enough into the exhaust pipe. A movement of about 5mm in the sensor towards the centre of the pipe produced a drop of about 50 deg C and the EGT's of all cylinders were now similar.
As Steevo says you can waste a lot of time chasing EGT variations that really have no significance.

I would expect the EGT's in the climb to be lower than in the cruise as more fuel should be passing into the cylinders at higher power settings and the cylinders should be running rich rather than lean. A uniformly high EGT might be the indication of a potential issue elsewhere in the engine and continually running lean at high power settings is undesirable. One possible check would be to ensure that you have a full fuel flow at high settings. At your next annual or significant service just check that the electric pump is capable of giving a fuel flow of 60 litres/ hour or more. I usually check at the fuel output of the engine fuel pump. I can't recall what the required maximum flow rate of the 2200 is but I suspect that it is under 30 litres per hour so the electric pump should easily be able to provide this.

The other possibility is that as the engine shifts in the climb there is a small air leak that is weakening the mixture. Almost the only likely candidate for this is the rubber connector between the carb and the engine. I have seen a case where the engine moved slightly in its mount under power and that put sufficient pressure on this gasket to open up a split and let extra air into the system. Seeing the split can be very difficult but it is worth looking at this gasket very carefully at the next opportunity as they do split particularly if it has been overtightened.

Other than those two ideas (a split in the carb rubber is my favourite) I would just check the colour of the plugs and be alert for any other symptoms. EGT's give vague hints rather than conclusive information and you can waste a lot of time chasing problems that don't exist.

Hope this helps

Peter
P.S the SP470 is a nice airframe and engine
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Re: EGTs during climb? Jab 2200A

Postby PKnight » Mon Oct 29, 2018 3:51 pm

Update.
On page 11 of the engine manual for hydraulic lifter engines the following data is given:-

EGT's in Cruise
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Re: EGTs during climb? Jab 2200A

Postby PKnight » Mon Oct 29, 2018 3:53 pm

Update.

On page 11 of the engine manual for hydraulic lifter engines the following data is given:-

EGT's in Cruise 680 to 750 deg C
EGT's in climb 640 to 780 deg C

So yours are within range even if it a bit on the wide side as ranges go!

Peter
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Re: EGTs during climb? Jab 2200A

Postby Steevo » Mon Oct 29, 2018 7:49 pm

I wonder why they changed it. That would make perfect sense as it’s roughly what I get on mine. I had not seen that change.

But having said that, 2 of the engines I have the data from are solid lifter. Mine is hydraulic and my EGTs go high when in a climb. On full power they are fine if level but not in the climb.

To me it makes sense as Jabiru also say that you can adjust the side to side temperatures by tilting the carby. So it would make sense that by raising the nose, you are essentially tilting the carby backwards.

In cruise, mine are around the 680-700 mark, in a climb at least one of them reaches about 780 with the rest spread between 750 and 760.
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Re: EGTs during climb? Jab 2200A

Postby Ican » Sun Nov 04, 2018 6:43 am

Here are two interesting articles that say essentially the same thing. Makes for very interesting reading. Use it or don’t...

http://www.gami.com/articles/egt_myths.pdf

https://www.savvyanalysis.com/articles/ ... ht-and-egt
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