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  #11  
Old 07-31-2011, 10:47 PM
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Well, that's kind of the mystery David... At low altitude I can get the LOP values well within a 10 degree spread (often besting my "low altitude" picture in the first post). The cylinders fall right in line as well with a fairly even spread. As I go high, the EGT splits (as shown) between the 1-3 and 2-4 (left side, right side). The thinner air makes cooling more difficult, but it does seem that EGT is driving the CHT to some degree. Trying to keep my "hottest" EGT cooler than 50 drives the outliers way cold, and the CHT's follow. And yes, the oil cooler is on #4, which I agree does not make sense. I almost started thinking the thermocouples were bad, but they are dead on at ambient, and also at low altitude. I'm not ruling it out, but a bad T/C is not high on my list of probabilities

It's kind of a chicken vs. egg thing. I'm not sure what drives what, but once it splits, it is very hard to get CHT and EGT to play nice again.
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  #12  
Old 08-01-2011, 06:13 AM
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Quote:
Originally Posted by Toobuilder View Post
Not sure I follow you there Dan... Do you mean to say that at such low fuel flows, the nozzle ceases to perform a metering function, and the flow divider becomes more influential?
Yes.

I looked it up in my email and found my mind had slipped only a little

Don said that with 0.028" nozzles the divider would control fuel split below 7.5 gph (not 7 gph). Obviously this is with an AFP system. Don't know about the others.
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  #13  
Old 08-01-2011, 08:11 AM
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Michael,
You might have a couple of spark plugs/wires or coils misfireing at high altitudes. That can cause higher EGT readings.Try running on one EI and then the other and look for any engine roughness.
I had a spark plug that would run fine until I reached 7000 ft. then start to misfire.
Good luck,
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  #14  
Old 08-01-2011, 09:17 AM
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Rich,

I did a mag check several times in cruise and got the expected EGT rise when operating on the single plug (either one). No roughness, but a definate rise in EGT indicates that both ignitions are working well.
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  #15  
Old 08-01-2011, 09:26 AM
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Quote:
Originally Posted by DanH View Post
Yes.

I looked it up in my email and found my mind had slipped only a little

Don said that with 0.028" nozzles the divider would control fuel split below 7.5 gph (not 7 gph). Obviously this is with an AFP system. Don't know about the others.
So perhaps the trick is to reduce the nozzle orifice enough to increase pressure and overcome the influence of the divider (more pressure at the nozzles than the divider), yet still be big enough to supply the max power requirements at sea level?

...There may not be enough "reserve" pressure in the current system to provide fuel through smaller nozzles at high power. Maybe Don will jump in here.

So the question of the day: For those that run LOP, do your engines behave like this at altitude? I have a stock system, so it stands to reason that many others should be seeing this.
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  #16  
Old 08-01-2011, 01:37 PM
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Originally Posted by Toobuilder View Post
So perhaps the trick is to reduce the nozzle orifice enough to increase pressure and overcome the influence of the divider (more pressure at the nozzles than the divider), yet still be big enough to supply the max power requirements at sea level?
That is my understanding, although perhaps not so simple in practice.

I am curious. Although perhaps not directly relevant to a temperature split, what do your CHT values look like when running a best power mixture, say 100-150 ROP? Must you run LOP to get acceptable temperatures?
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  #17  
Old 08-01-2011, 02:03 PM
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That's a good question Dan... I can't recall ever running it that rich for any length of time in cruise. Climb mixture is generally fat, but the speed is so low that CHT is meaningless. ...I'm just trying to get the climb over with so I can go LOP and cool off. I can tell you that LOP is not required to keep temps in check, but I don't know how they compare to ROP vs. LOP. I guess I'll have to go out and try flying at best power and see what it does.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

Michael Robinson
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1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 08-01-2011 at 02:08 PM.
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  #18  
Old 08-01-2011, 05:55 PM
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Originally Posted by Toobuilder View Post
That's a good question Dan... I guess I'll have to go out and try flying at best power and see what it does.
Ok, I ask because of the CHT's in the first photos (at 12,500 feet): 380, 357, 395, and 322, and your comment "Trying to lean further to bring #3 under control would cause the already too cold #4 to plummet further.".

First, best power ROP is a more difficult cooling case, as is a higher altitude (lower density). If you're leaning to get #3 down to 395, it's not going to be good at best power.

Second, compared to your reference cylinder (the cool #4) 1 and 3 are always warm....about 40 degrees in the low altitude case and 60-70 in the high altitude case.

There's a temptation to search for THE problem, but most of the time it's a little of this and a little of that. I'd suggest going back for a look at the baffles before worrying too much about a fuel flow inbalance at low volume that you may not be able to solve.
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  #19  
Old 08-01-2011, 07:32 PM
DENMACRES DENMACRES is offline
 
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Smile fuel flow

I went to .024's to solve the divider issue, but there was a significant drop in full power on my modified IO-360 (ported, flowed and upped comp.) I have went back to larger inserts. Pulling the throttle back at alt. until the MP just starts to fall will help even the EGTs. (old racer trick) Dennis McCright 936-443-3562 RV-6,900hrs. LOP, 172kts, 6.9gph at 10,000 Have fun out there.
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