High CHT temps on 0-340

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BDA
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High CHT temps on 0-340

Post by BDA »

I have been trying to get the breakin done on the plane and am having a difficult time getting to full throttle due to CHTs going over 450*.

I can run 1,800-2,100 and they stay below 360 or so.

The factory has since gone to a different carb to help w cooling so I am thinking that is the problem - but - I have been reading on the Vans forum that the P-mag timing advance happens right in that rpm range, and without leaning for altitude the timing is burning fuel at a rate that causes high CHT.

So they are reducing timing.

I also read that if manifold presure is correct the timing is not an issue.

Do any of you have any experience with this??
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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danerazz
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Re: High CHT temps on 0-340

Post by danerazz »

Those sound crazy high for CHTs. I am not familiar with p-mags but I cannot imagine the MP has nearly as much to do with timing as RPM. The idea is you control where peak pressure occurs with timing. MP does affect how fast the charge burns, so it is not inconsequential, but at higher RPM the piston passes TDC before combustion has a chance to push pressures up high enough for detonation. The standard magneto fixed timing is not good at high power settings, but won’t allow the engine to be destroyed. If your timing is causing significant CHT rise, you would be dangerously close to detonation if not already there.

There are numerous articles about this.

As for the carb, if it is capable of enriching at least 100 degrees or more below peak I would not think it would be a carb issue. If the carb is just too small for you engine and can’t supply enough fuel for the horsepower, or if there is an up-stream fuel restriction causing lean mixture at higher power settings, then you would see excessive CHT.

I know many MFGs state CHT redlines well above 400, the aluminum heads can suffer long term damage above 400 especially at high power settings. 450 at high power seems brutal to me for any engine.

In short, your description would have me looking very closely at how the P-mag advances timing, followed by a close study on your fuel flow at same power settings.

My advice is worth what you pay for it.
Dane

Paralysis by analysis
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

Thanks Dane
The Cht redline for the motor is 500*, but 475 is considered the limit. So I havent gone too far yet, just trying to be cautious.
From what I am reading it sounds like 5* past TDC is the accepted fix. But still looking at MAP.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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danerazz
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Re: High CHT temps on 0-340

Post by danerazz »

I don’t know the ins and outs of that particular series of engine, but for a Ly-Con clone engine that sounds crazy high for CHT.

Based on your description of the relatively rapid CHT rise over rpm rise, it certainly SOUNDS like a timing issue.

I’ll be really interested to see what you come up with for a fix.
Dane

Paralysis by analysis
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stede52
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Re: High CHT temps on 0-340

Post by stede52 »

BDA wrote:Thanks Dane
The Cht redline for the motor is 500*, but 475 is considered the limit. So I havent gone too far yet, just trying to be cautious.
From what I am reading it sounds like 5* past TDC is the accepted fix. But still looking at MAP.
I've got a Carboncub with Titan 340 using the Lightspeed electronic ignition which is set at 25 degrees TDC. I've never had heating issues with mine however, 450 degree CHTs during break-in is definitely a NO,NO for us! When CC airplanes are having a CHT heat issue one of the first things they do is retard the timing back to 22.5 TDC, which seems to reduce CHT heat substantially. Carburetor fuel atomization also cause some 340 issues before they upgraded the spray bar in the carb.
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danerazz
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Re: High CHT temps on 0-340

Post by danerazz »

BDA wrote:Thanks Dane
The Cht redline for the motor is 500*, but 475 is considered the limit. So I havent gone too far yet, just trying to be cautious.
From what I am reading it sounds like 5* past TDC is the accepted fix. But still looking at MAP.
On second read, 5* PAST TDC sounds crazy late! Even 5* BEFORE TDC would be extremely late.
Dane

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BDA
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Re: High CHT temps on 0-340

Post by BDA »

To clarify,
The data tag on motor says time for 25* advance.

The Pmags have 25* advance built into program.

So when you set timing, you are telling the computer where TDC is.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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danerazz
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Re: High CHT temps on 0-340

Post by danerazz »

Thanks, I did a little research on them (never used them, but read about them) and your numbers make a lot more sense! I just wasn’t thinking when you time them you set TDC. New fangled voo-doo.
Dane

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BDA
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Re: High CHT temps on 0-340

Post by BDA »

I had a friend stop by the plane yesterday and say that he got cooler temps by sealing up the air intake and spinner / crank gaps

So I cut a piece of 2” wide rubber baffle material and wrapped it around and screwed it to the air filter cage so that it tucks into the lip of the intake scoop when cowl is installed.
Then I installed the spinner that I had for it.

CHTs are still high but slower to get there, and cool down much faster, when I back off the throttle.

BUT
My oil temps are 20* cooler!!

So this is a definite must do for the Titan.

When I pulled my plugs they did not have as much brown as I expected, so the next step is to send the carb in to Marvel to have the jets opened up to make it richer.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

I taped a 2” aluminum extension to the lip at the bottom of the cowling to try and create more low presure or suction to force more airflow past the cylinders.

Then I flew a full lap around the pattern at 2,500 rpm, CHT was climbing past 450* when I pulled it back to 2,400, then I did another lap. CHT stayed between 440 and 450. Oil temp climbed to 220 after 3 laps and stayed there.

When I pull throttle back to 2,300 temps go to 430, at 2,200 temps are 400-410, below 2,200 temps stay around 360.
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SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

For those familiar with the E-mag or P-mags, they have an auto advance of 25* as I mentioned earlier, AND they have a performance mode that has 5* more advance.
But you have to pick one or the other. But being clever, I put a switch on the panel so I can toggle back and forth as needed.

Nothing new there, pretty common to do this.
I was very deliberate, when installing the switch, and checked twice that the Perf mode was up, as labeled by the wire guys.

So I was thinking about the timing being a possibility for my high CHTs, and it made me wonder if the performance mode was “on”.

So I flipped the switch and took it for a flight.

Flew for 20 min at 2,500 rpm and CHTs never went above 440, that is the first time I have been able to go more than a few minutes at 2,500 without going past 450.

So I am super stoked that my temps are “normal”!!!!

And super embarrassed that I had the switch backwards.

I told myself that I would not use “performance mode” until after breakin, so I was hesitant to flip the switch. Turns out I have been in performance mode this whole time.

I will verify with a few more flights.

Thats just stupid
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

Well, I put an hour and a half on the plane yesterday, temps are all good now.

I also switched the ignition advance back to performance mode - that was marked normal mode - and saw a performance gain and higher temps, so there is no doubt that the switch is backwards.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

Update:
1 yr later
The Pmag ignition timing advance is obviously creating more heat when it advances.
I saw 420-430 with 0* TDC start timing. Still do.
At the request of my AnP I reduce start timing 5* so that the auto advance would not cause as much heat, it worked well.
Temps at 2450 were 380-390

This spring I wanted the hp back, so I reset the timing to zero- and I am back to 420 at 2450.
So I blocked off the oil cooling air duct off the back of the plenum, and rerouted oil cooling from somewhere else.
Now that I am not robbing air from the plenum the back cylinders run almost 20* cooler. It worked!
But now my oil temps are high.

On the Titan engine - DO NOT pull air off the plenums.
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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BlainS
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Re: High CHT temps on 0-340

Post by BlainS »

Are all cylinders even? I’m not convinced the isolated plenum is the way to go. My plan is to use Vans baffle kit.
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BDA
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Re: High CHT temps on 0-340

Post by BDA »

3 and 4 (back 2) were the highest before I plugged the ports

Now #2 is 10-15* higher now
SuperStol XL Alaskan With Titan 340
N331AK. Shawn Taplin
Wing extensions,Symetrical Airfoil tail ribs (NACA 21)
Mods in progress: Heavier struts, Double slotted flaps
Goal: 15mph no wind
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