Have you tried your timing @24deg to address CHT overheating?

[YuriE]

Has anyone followed Mike Busch advice and set timing to 24 deg from TDC to try address CHT crossing 400? If you did - could you share your experience?

[takair]

I have not specifically done it on a C model, but on my E model it has the 20 deg SB and runs almost too cool. The less the advance the cooler it will run. Not sure how much 1 degree timing will get you but it won’t hurt. For that matter, you may actually be at 26 so you might get two degrees. Not hard to do at annual when they check timing anyways. 

[MikeOH]

How much power is lost when going from 25 to 20 deg advance?

[PT20J]

1 hour ago, MikeOH said:

How much power is lost when going from 25 to 20 deg advance?

If we assume that 25 degrees BTDC is the optimum timing to achieve maximum brake torque, then according to Heywood, Internal Combustion Engine Fundamentals, 1988, Figure 15.3, retarding timing by 5 degrees would reduce power by about 1%. 

[PT20J]

Common practice is to set mag to engine timing within 1 degree, so I assume that Mike picked this number because it is within normal tolerances and won't affect starting. It might be worth a try to see if it lowers temperatures, but it is such a small change (assuming timing is correctly set to begin with) that it might not make a difference. If you want to go all the way to 20 deg, it would require a different left mag with a reduced lag angle and remarking the data plate per Lycoming SI 1325.

SI 1325 Timing Change for IO-360 Series Engines.pdf

[PA24Lvr]

Interesting topic.  We had a turbocharged 182 in for annual, there is a Lycoming S/I to advance the Tim in from 20 to 23 degrees for a slight performance bump.

Clarence

[takair]

8 hours ago, MikeOH said:

How much power is lost when going from 25 to 20 deg advance?

I suppose there is a slight loss, but I don’t have numbers to compare.  I feel like my plane does pretty good for speed and climb.  I added a Surefly a few years ago and with the advance I get the power back in cruise.  I think Lycoming put out SI1325 to eliminate the possibility of detonation….i think it effectively reduces the so called red box.  

[YuriE]

14 hours ago, takair said:

I suppose there is a slight loss, but I don’t have numbers to compare.  I feel like my plane does pretty good for speed and climb.  I added a Surefly a few years ago and with the advance I get the power back in cruise.  I think Lycoming put out SI1325 to eliminate the possibility of detonation….i think it effectively reduces the so called red box.  

My problem is mostly at take-off, and I got mechanic set 24 as per Busch. I don't see any effect either on power or on CHTs that I can discern...

[takair]

2 minutes ago, YuriE said:

My problem is mostly at take-off, and I got mechanic set 24 as per Busch. I don't see any effect either on power or on CHTs that I can discern...

C models tend to run much warmer than E and F no matter the timing. I think low 400s on climb is pretty normal for a C. 

[hammdo]

Yep, depending on how hot it is outside, CHT management is a necessity. 400’s are not uncommon. 
 

-Don

[MikeOH]

22 hours ago, PT20J said:

If we assume that 25 degrees BTDC is the optimum timing to achieve maximum brake torque, then according to Heywood, Internal Combustion Engine Fundamentals, 1988, Figure 15.3, retarding timing by 5 degrees would reduce power by about 1%. 

And, for those that don't have their copy of Heywood's Internal Combustion Engine Fundamentals handy (I didn't), here's an excerpt from Taylor's, The Internal Combustion Engine in Theory and Practice, 1960, Figure 12-14, pg. 443:

 

[YuriE]

12 minutes ago, takair said:

C models tend to run much warmer than E and F no matter the timing. I think low 400s on climb is pretty normal for a C. 

Thx for responding... That's what I'm hearing, and yet Busch keeps pushing below 400 for longevity... How am I supposed to achieve that on #2? I read all over the place, that #2 goes over 400 on take-off, and that's exactly what I get... 

[YuriE]

3 minutes ago, hammdo said:

Yep, depending on how hot it is outside, CHT management is a necessity. 400’s are not uncommon. 
 

-Don

So - should I just live with it then, and make sure it's not for too long?

[MikeOH]

4 minutes ago, YuriE said:

Thx for responding... That's what I'm hearing, and yet Busch keeps pushing below 400 for longevity... How am I supposed to achieve that on #2? I read all over the place, that #2 goes over 400 on take-off, and that's exactly what I get... 

I've fought high temp on cylinder #2 on my F model since I bought it 8 years ago.  Same deal, in climb on a hot day #2 will go over 400; I've seen as high as 415.  I have tried just about everything but adjusting the timing.  But I've just learned to live with it; generally, if I maintain 120 mph in climb it will stay <410 and start to drop from there once I'm above 3500-4000 DA.

[hammdo]

I make sure full rich, then lower nose once cleared of obstructions, reduce RPM to 2600 or 2500 as needed. I have new cylinders so I do what I can to keep temps around 405° or lower… sometimes it hot - up to 415° . but I’m quick to get it managed…

-Don

[MikeOH]

3 minutes ago, YuriE said:

So - should I just live with it then, and make sure it's not for too long?

Exactly what I've done.

[takair]

There is nothing magic about 400 except that Savvy flags it. I have a friend who is religious about it in another aircraft type but he is giving up tons of performance on every flight. Done the timing, baffles, carb.  My guess is he would peak at 420 and the engine would be happy. Instead he accepts reduced rate of climb, which creates its own hazards.  Many airplanes continue to operate without analyzers and make TBO and beyond. Look at flight schools. Yeah…..there is a point where you eat into cylinder life but 400 or 410 won’t instantly cause that. Find out where you sit. If you are at 430….you can probably improve…based on other C models. But 410 and 420 seems to be where they end up in climb. An E model at 400 would be hot. A C model at 400 is just warm. The carb and intake system just wasn’t well tuned at the time. 

[bonal]

For my D it’s completely normal for a climb temperature of around 400 degrees.  Slightly higher on warm days and lower on cold days.  I only have the original gauges so accuracy is somewhat questionable however the gauge is going to be consistent to itself.  I have been climbing at 2500 vs 2700 and to illustrate the difference in temperature at 2700 the needle is just above the 400 degree line and at 2500 it’s just below the line always at 120mph or higher. I don’t know what that means in terms of temperature but it’s definitely lower.  My climb performance is reduced by about 1 to 2 hundred feet per minute.  Still better than 600 FPM fully loaded.  My question about regarding the timing is can we just do this in other words every aspect of our airplanes and engines is HIGHLY REGULATED so is this even permitted.  As for me it is what it is I do my best to keep an eye on it and fly accordingly.

[Skates97]

1 hour ago, hammdo said:

I make sure full rich, then lower nose once cleared of obstructions, reduce RPM to 2600 or 2500 as needed. I have new cylinders so I do what I can to keep temps around 405° or lower… sometimes it hot - up to 415° . but I’m quick to get it managed…

-Don

I've played around with it a lot and found the best combination was to leave prop full forward and reduce MP to 24-25" after take off. 

I frequently saw 420-430° with my old engine in climb and replaced it at 2,336 hours just because I wanted to do it on my timeline and not when it decided it needed to be replaced. It was still running fine with compressions 77+ and no metal in the filter when it was replaced. The new engine had some issues running hotter and had to manage it to keep it under 440°. I found the bottom baffles on #3 and #4 weren't quite right. After that I still see 420-430° initially in the climb on #3 but it cools down and I'm not concerned.

[PT20J]

1 hour ago, YuriE said:

Thx for responding... That's what I'm hearing, and yet Busch keeps pushing below 400 for longevity... How am I supposed to achieve that on #2? I read all over the place, that #2 goes over 400 on take-off, and that's exactly what I get... 

If it's only during takeoff and climb, I wouldn't worry about it. A local flight school has a fleet of well-maintained older C-172s. They regularly achieve TBO. They never had factory CHT gauges, and so no one knew what temps they were getting. A few years ago, the owner had G3X/EIS installed in a couple of them. Now everyone knows that the CHTs are above 400F during a takeoff and climb. 

[takair]

7 hours ago, bonal said:

For my D it’s completely normal for a climb temperature of around 400 degrees.  Slightly higher on warm days and lower on cold days.  I only have the original gauges so accuracy is somewhat questionable however the gauge is going to be consistent to itself.  I have been climbing at 2500 vs 2700 and to illustrate the difference in temperature at 2700 the needle is just above the 400 degree line and at 2500 it’s just below the line always at 120mph or higher. I don’t know what that means in terms of temperature but it’s definitely lower.  My climb performance is reduced by about 1 to 2 hundred feet per minute.  Still better than 600 FPM fully loaded.  My question about regarding the timing is can we just do this in other words every aspect of our airplanes and engines is HIGHLY REGULATED so is this even permitted.  As for me it is what it is I do my best to keep an eye on it and fly accordingly.

The suggested timings are within the type certificate limits, so 100% allowable. In the case of the OP, at most he would gain 2 degrees timing advantage. As suggested, improvement would be marginal. In my case, 20 degree timing was a Lycoming bulletin. In this case it is actually a little harder ti go back to 25 degree because the data plate is remarked. I’ve never really seen the need, especially with Surefly. That said, if I lived at a high density altitude airport I might consider it. I’m at sea level so plenty of margin. 

[Utah20Gflyer]

TThe 400 degree limit seems to apply to Continental engines because their cylinders aren’t built as strongly as Lycoming.  I believe I’ve heard Mike Busch talk about that and he said low 400s during takeoff would be fine for a Lycoming powered aircraft.  Personally I try to keep temps at 400 but in the summer I’ll go up to 420 without worry.   

[kortopates]

TThe 400 degree limit seems to apply to Continental engines because their cylinders aren’t built as strongly as Lycoming.  I believe I’ve heard Mike Busch talk about that and he said low 400s during takeoff would be fine for a Lycoming powered aircraft.  Personally I try to keep temps at 400 but in the summer I’ll go up to 420 without worry.   

It’s not a strength issue but different design. The lycoming cylinder exhaust valves filled with sodium transfer the majority of their heat through the valve guides with a Savvy recommended redline of 420F. Continental exhaust valves are conventional solid stem and transfer the majority of their heat through the seat which isn’t as effective with a Savvy recommend redline of 400F. Hence the greater preponderance of burned valves with Continentals but rarely sticky valves which are common on Lycoming cylinders. Different designs and different tradeoffs.


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