C model CHT's

[Shadrach]

Anthony, maybe he was looking in the Owner's Manual. Here's my Performance Chart for sea level, with the highest fuel flows.

I'd love to see a chart of strength vs. temperature for aluminum, especially if it had been done with an aircraft engine instead of a dogbone.

Sabremech's new cowl is very interesting, although he is being coy with pricing until after STC approval. This is quite reasonable to me. I wonder if he has a target price in mind?

That POH figure is for a standard day. What's the FF for a C model on a high pressure February day at Sea Level with an OAT of 14df? It should be Significantly more than 18.2

Edited October 27, 2015 by Shadrach

[Hank]

True. That's probably why he ballparked it at 18½ gph. I have no way to find the number you are asking for . . . no fuel flow.

[Taracka]

What I meant is according to the fuel flow function on my JPI EDM 700 I am burning 18.5 gph on takeoff from a density altitude of 250 feet.  When I spoke with the folks at Marvel Schebler they indicated that should be about right for an o360 a1d and was likely not the culprit for high CHT's

[Shadrach]

Rick,

Marvel Schebler has been making carbs for Lycoming engines for at least half a century. They make a quality product but are not what I would call on the cutting edge of aviation tech. I don't know what their goals were when they spec' the O360, I do know that >400df CHTs were perfectly acceptable to pilots in the 50s, 60s, 70s and 80s. There has been a bit of a renaissance in engine monitoring tech in the last 25 years, and consequently a reassessment of what settings are best for engine health. I'm not so sure that Marvel Schebler got on the train... 

Every cylinder should be at least 250 ROP on take off and initial climb. That means all EGTs must be under 1300df, preferably more (all cyl on my IO360 A1A run in the mid 1100s save for #3 which is just over 1200).  Raw EGT numbers do matter on take off and climb. If you have not verified that all cylinders are 250ROP or more than you are pissing in the wind trying to solve the issue with the cowling.

Edited October 28, 2015 by Shadrach

[DXB]

 

Every cylinder should be at least 250 ROP on take off and initial climb. That means all EGTs must be under 1300df, preferably more (all cyl on my IO360 A1A run in the mid 1100s save for #3 which is just over 1200).  Raw EGT numbers do matter on take off and climb. If you have not verified that all cylinders are 250ROP or more than you are pissing in the wind trying to solve the issue with the cowling.

Help - I'm confused by this statement.  Admittedly I'm pretty inexperienced with these topics and just starting to scrutinize the downloads from my new JPI, so please humor me.  On takeoff and initial climb on my O-360-A1D, I routinely have 1 cylinder with EGT that exceeds 1400- usually #3 which has the hottest CHT (430) but sometimes it's #4, in which case this cylinder CHT runs hot around 420, and #3 runs cooler (390s).  I don't think it's plug fouling on #3 vs #4 that variably raises the EGT, as it always correlates with high CHT on the same cylinder.  And its not a partly clogged injector, as it's carbureted.  

So I was worrying a bit about my high and variable EGTs during WOT climb, before I read the following Mike Busch article: http://www.gami.com/articles/egt_myths.pdf   He basically says one must ignore absolute EGT since so many dynamic variables impact the probe readings other than actual exhaust temperature.   Am I correct in feeling better? I'd still love someone to explain why sometimes #4 decides to be the hottest on climb, and #3 decides to run <400 in these cases- maybe some weird shift in mixture distribution? I'll likely pay for the Savvy analysis service after I collect some more data...

 

[Shadrach]

Help - I'm confused by this statement...

I read the following Mike Busch article: http://www.gami.com/articles/egt_myths.pdf   He basically says one must ignore absolute EGT since so many dynamic variables impact the probe readings other than actual exhaust temperature.   Am I correct in feeling better? I'd still love someone to explain why sometimes #4 decides to be the hottest on climb, and #3 decides to run <400 in these cases- maybe some weird shift in mixture distribution? I'll likely pay for the Savvy analysis service after I collect some more data...

 

All of the engine gurus say that absolute EGT numbers don't matter. I agree with that when leaning or when comparing one cylinder to the next. Probe placement does affect raw numbers. But you know what differences in probe placement won't do? It won't show heat that's not there. Follow that thinking for a moment on your #3 EGT. If your JPI shows that #3's EGT is 1400+ then the actual EGT must be at least whatever the JPI shows. The reading might show 20-60 degrees cooler than it actually is due to probe placement, but it's not likely to show hotter than it actually is. Can you guess where #3 might peak? Unless it's well over 1600, I would think that that cylinder is running leaner than ideal at WOT on take off.

Also, If this were a plug fouling, you'd likely see quite a bit more than mid 1400s.

If I were you, I'd shoot Mike an email. Tell him your numbers. He may say that I'm all wet. I used to occasionally trade emails with  John Deakin regarding these matters. I would try him, but I don't think he's as active as he once was.

The IO360 is a slightly higher compression engine than the O360. It should theoretically produce slightly higher peak EGT numbers. My EGTs at WOT takeoff are almost always in the mid to high 1100s sometimes #3 exceeds 1200. I lean in climb to maintain performance, but keep CHTs under 360. I would abort my take off if I saw an EGT in the 1400s

[DXB]

All of the engine gurus say that absolute EGT numbers don't matter. I agree with that when leaning or when comparing one cylinder to the next. Probe placement does affect raw numbers. But you know what differences in probe placement won't do? It won't show heat that's not there. Follow that thinking for a moment on your #3 EGT. If your JPI shows that #3's EGT is 1400+ then the actual EGT must be at least whatever the JPI shows. The reading might show 20-60 degrees cooler than it actually is due to probe placement, but it's not likely to show hotter than it actually is. Can you guess where #3 might peak? Unless it's well over 1600, I would think that that cylinder is running leaner than ideal at WOT on take off.

I would abort my take off if I saw an EGT in the 1400s

Ross- It seems hard to define the standard for an "actual" EGT - perhaps one measured at the lip of the exhaust valve seat at the instant the valve opens?  Anything past that, the gas is rapidly expanding, cooling, and sensitive to variations in the environment it is passing through.  Mike Busch cites "cam lobe profile, lifter leakdown rate, valve spring condition, and exhaust manifold topology, among others" as variables- admittedly one or two of these terms  are over my head.  

Anyway, it sounds like a 1400 EGT on takeoff would be a scary aberration from what you normally see. Yet this seems par for the course for me. So I'm wondering if my cylinders are dangerously lean at WOT? Going against this possibility is that #3 or #4 do not even appear to be my leanest cylinders- #2 usually peaks first when I lean in cruise at 65-75% power. Could mixture distribution be very different at WOT vs cruise in my engine? Again, I'm in over my head here, but the lack of precision from my carburetor vs your injectors seems to add more variables in my case.  

[Hank]

Yes, the mixture delivered to our cylinders is much more variable than our injected brethren. And moving the throttle will do several things, most of which are due to airflow through the carb being reduced. Less air means that the stream of fuel,being pumped in is not atomized as well, having both larger droplet size and more variation in droplet size (there are more large droplets, but still many small and tiny ones). These droplets are then scattered and sent to the cylinders to be burned. Drop size varies more at reduced throttle, so the fuel in each cylinder at any given time varies, as does the amount sent to each cylinder (the air-fuel mixture is less homogenous, and distribution between cylinders varies more).

for years, I was a believer in pulling the throttle back in cruise enough to move the MP needle, hoping to both shut off the full-throttle auto enrichment circuit and create turbulence inside the throttle for better atomization and more mixing. At the recent Summit, Bob Kromer said to try running WOT anyway, and it should only reduce my range by ~40 nm. I tried it coming home from KECP, used the same 14 gals I did going down. Need to try more, maybe a longer flight.

good luck diagnosing what's going on. Just expect your carb'ed engine to run differently from an injected one. And please let us know if you find anything definitive!

[Shadrach]

Ross- It seems hard to define the standard for an "actual" EGT - perhaps one measured at the lip of the exhaust valve seat at the instant the valve opens?  Anything past that, the gas is rapidly expanding, cooling, and sensitive to variations in the environment it is passing through.  Mike Busch cites "cam lobe profile, lifter leakdown rate, valve spring condition, and exhaust manifold topology, among others" as variables- admittedly one or two of these terms  are over my head.  

Anyway, it sounds like a 1400 EGT on takeoff would be a scary aberration from what you normally see. Yet this seems par for the course for me. So I'm wondering if my cylinders are dangerously lean at WOT? Going against this possibility is that #3 or #4 do not even appear to be my leanest cylinders- #2 usually peaks first when I lean in cruise at 65-75% power. Could mixture distribution be very different at WOT vs cruise in my engine? Again, I'm in over my head here, but the lack of precision from my carburetor vs your injectors seems to add more variables in my case.  

Dev,

I would abort a take off at 1400° for sure. However, that's mostly because it would be 250° higher than normal leading me believe I had an obstructed injector. What is your typical peak EGT on that cylinder? If you leveled off at 1000ft AGL and leaned until #3 hit peak, do you think you'd be 1650° or greater (250°ROP).  What's important is that the engine is adequately rich at its most demanding setting. That extra fuel slows the combustion event and lowers peak cylinder pressure (what typically causes high CHTs). In short, slowing combustion with fuel (or air when LOP) creates a more even push throught the power stroke as opposed to a hammer blow just after TDC. I don't think there's any mystery to your high CHT with EGTs in that range, but there could be a bunch of stuff I don't know about carbureted engines. Perhaps the cylinder to cylinder variations are great enough that it's the best that can be achieved.

Your C's CHTs differ little from others given what I've read here. Does that mean it's optimal? Can it be improved upon? They are 100° higher than what I'm used to seeing. Your take-off EGTs are >200° higher than what I'm used to seeing. Some of my EGTs peek in the high 1400° range.  Seems to me high take-off EGTs and high take-off CHTs are correlated. If everything else is performing as it should, then the correlation is likely the cause. What's odd to me is that folks are chase baffling leaks and condemning the cowling but not focusing on what's causing the heat.

I would email Mr. Bush. I would also talk to the folks at Marvel Schebler.

I'm not saying there's anything wrong with your plane, but maybe you can improve your operating temps and set a new bar for how optimally these engines can be run.

This is an excerpt from a column written decades ago by John Deakin, a man who's writings I've read religiously:

"I will also repeat from the previous column, YOU MUST BE GETTING FULL REDLINE FUEL FLOW at full takeoff power AT SEA LEVEL! In truth, the factory redlines are often a bit on the low side, and flows should be tweaked up just a bit. Even a half-gallon per hour makes a BIG difference in CHTs during climb.

In general, and speaking very roughly, if you see EGTs anywhere over about 1,300°F (lower will not hurt a thing and is probably “better”) during a sea-level takeoff, or CHTs above about 360°F right after takeoff, YOUR FUEL FLOW IS TOO LOW. Having a good understanding of the proper relationship between the EGTs and the fuel flow at very rich mixture settings will always give you a good cross-check on whether or not you are getting adequate fuel flow -- even if your fuel flow needle breaks off and falls to the bottom of the instrument!"

 

[Shadrach]

Yes, the mixture delivered to our cylinders is much more variable than our injected brethren. And moving the throttle will do several things, most of which are due to airflow through the carb being reduced. Less air means that the stream of fuel,being pumped in is not atomized as well, having both larger droplet size and more variation in droplet size (there are more large droplets, but still many small and tiny ones). These droplets are then scattered and sent to the cylinders to be burned. Drop size varies more at reduced throttle, so the fuel in each cylinder at any given time varies, as does the amount sent to each cylinder (the air-fuel mixture is less homogenous, and distribution between cylinders varies more).

for years, I was a believer in pulling the throttle back in cruise enough to move the MP needle, hoping to both shut off the full-throttle auto enrichment circuit and create turbulence inside the throttle for better atomization and more mixing. At the recent Summit, Bob Kromer said to try running WOT anyway, and it should only reduce my range by ~40 nm. I tried it coming home from KECP, used the same 14 gals I did going down. Need to try more, maybe a longer flight.

good luck diagnosing what's going on. Just expect your carb'ed engine to run differently from an injected one. And please let us know if you find anything definitive!

A carbed engine doesn't really run differently than its injected brethren, it's just not as precise.  It doesn't take a lot of fuel to make a 200° difference in EGT. I don't think any cylinder is happy at sea level max power unless it's a minimum of 225° ROP.  A cylinder will certainly run well much richer than that. I would rather see EGTs in the 1050° to 1200° range than the 1300° to 1450° range. If I was running an O360, I'd find someone who would set it up that way. Fuel can always be removed with the mixture.

[carusoam]

Has anyone cleaned the blue goo out of the air/fuel intakes in their O360?

If you are familiar with the mess a fuel leak makes when fuel evaporates, picture what 52 gallons a week looks like. A heavy coating builds up from the carb to the valves.

This comes from my experience from my C's O360.  I did some cleaning while changing out the cork gaskets.  Years of build-up.

It would be interesting to see before and after JPI data on the effects of cleaning from carb to valves.

Best regards,

-a-

 

 

 

 

 

 

Edited October 29, 2015 by carusoam

[Shadrach]

Has anyone cleaned the blue goo out of the air/fuel intakes in their O360?

If you are familiar with the mess a fuel leak makes when fuel evaporates, picture what 52 gallons a week looks like. A heavy coating builds up from the carb to the valves.

This comes from my experience from my C's O360.  I did some cleaning while changing out the cork gaskets.  Years of build-up.

It would be interesting to see before and after JPI data on the effects of cleaning from carb to valves.

Best regards,

-a-

I've never heard of that. I run Avgas in my old Triumph motorcycle and the intakes remain clean. I have clear balance tube aft of the carbs that is still clear. The old O-rings in the petcocks did did not like avgas an created some external staining, but the intake path stays quite clean.

Edited October 29, 2015 by Shadrach

[carusoam]

Ross, That is why I'm asking.  It was a thick dark blue goo.  I would have been asking about acceptable carb or intake cleaning fluids if I still had the O360. A clear tube wouldn't be clear for very long...

Could be a function of how ROP the engine was run.  Running lean may drop the additives out more than running rich?

 

Best regards,

-a-

Edited October 29, 2015 by carusoam

[Shadrach]

Ross, That is why I'm asking.  It was a thick dark blue goo.  I would have been asking about acceptable carb or intake cleaning fluids if I still had the O360. A clear tube wouldn't be clear for very long...

Could be a function of how ROP the engine was run.  Running lean may drop the additives out more than running rich?

 

Best regards,

-a-

Cant imagine mixture setting mattered.  It had to happen while the engine was running given the updraft nature of the carb.  I hope that others will ring in.

Edited October 29, 2015 by Shadrach

[Marauder]

Ross- It seems hard to define the standard for an "actual" EGT - perhaps one measured at the lip of the exhaust valve seat at the instant the valve opens?  Anything past that, the gas is rapidly expanding, cooling, and sensitive to variations in the environment it is passing through.  Mike Busch cites "cam lobe profile, lifter leakdown rate, valve spring condition, and exhaust manifold topology, among others" as variables- admittedly one or two of these terms  are over my head.  

Anyway, it sounds like a 1400 EGT on takeoff would be a scary aberration from what you normally see. Yet this seems par for the course for me. So I'm wondering if my cylinders are dangerously lean at WOT? Going against this possibility is that #3 or #4 do not even appear to be my leanest cylinders- #2 usually peaks first when I lean in cruise at 65-75% power. Could mixture distribution be very different at WOT vs cruise in my engine? Again, I'm in over my head here, but the lack of precision from my carburetor vs your injectors seems to add more variables in my case.  

Dev - how far down on the exhaust pipes are probe installed?

Here is the installation manual page on the required distance:

And as for "normal" EGTs:

Sent from my iPad using Tapatalk

[Hank]

Ross, the EGT in my C typically peaks around 1500-1525ºF. It's slightly different now since we replaced the muffler and tail pipe at annual in January. It's ~1300ºF on takeoff; I'll verify this tomorrow afternoon, along with OAT and pressure at my 264' msl home field.

Our carbed engines have an auto-enrichment circuit that kicks in and delivers extra fuel when WOT. Misture is typically non-homogenous, and distribution could be better. Sometimes, depending on the phase of the moon, direction of winds aloft relative to flight direction, and whether the ISS is passing overhead or not, I can run very slightly LOP but never as much as a single mark on the EGT dial [25º]. That's life in a C, even with the guppy mouth closure, and it's why we are all watching David's new cowl thread with bated breath.

[Shadrach]

Ross, the EGT in my C typically peaks around 1500-1525ºF. It's slightly different now since we replaced the muffler and tail pipe at annual in January. It's ~1300ºF on takeoff; I'll verify this tomorrow afternoon, along with OAT and pressure at my 264' msl home field.

Our carbed engines have an auto-enrichment circuit that kicks in and delivers extra fuel when WOT. Misture is typically non-homogenous, and distribution could be better. Sometimes, depending on the phase of the moon, direction of winds aloft relative to flight direction, and whether the ISS is passing overhead or not, I can run very slightly LOP but never as much as a single mark on the EGT dial [25º]. That's life in a C, even with the guppy mouth closure, and it's why we are all watching David's new cowl thread with bated breath.

I understand how a Marvel Schebler aircraft carburetor works. It is a compromise. One must look at the engine as a collection 4 smaller engines working together. If Dev has a cylinder that produces an honest 1400° plus with the enrichment circuit engaged then I would be examining what effect additional fuel would have on the other cyl. If I could determine that my other 3 cylinders would run fine 100° richer,  you better believe I would have the carb adjusted. I think Sabermech's new cowl has a lot of potential, however I don't see the wisdom in hoping a cowl will solve what appears to be a fuel problem.

I look forward to getting your EGT data.

[N601RX]

Here is a link that has the cooling capacity curves for a given pressure differential for both the angle valve and parallel valve cylinders.  You can see the cooling capacity of each for a given airflow.

 

http://www.vansairforce.com/community/showthread.php?t=79961

Edited October 29, 2015 by N601RX

[Hank]

Thanks, Mike. So my O360 requires 28.5% more air flow through the cowl than your IO360. Wow! Or as Ross says, we can throw a lot of extra fuel at the engine and try to draw some of the heat out the tailpipe. No wonder we have higher EGT & CHT than our injected brethren.

[M20F]

Yeah I'd be very curious to know from the engine experts on here  if and why O-360s and IO-360s cool so differently inside the same doghouse.  

They cool differently because they are two very different engines, you can't really compare the two.  Fuel injection alone makes a huge difference in how hot/cold a cylinder will run.  

[DXB]

What is your typical peak EGT on that cylinder? If you leveled off at 1000ft AGL and leaned until #3 hit peak, do you think you'd be 1650° or greater (250°ROP).  

 Some of my EGTs peek in the high 1400° range.  Seems to me high take-off EGTs and high take-off CHTs are correlated. If everything else is performing as it should, then the correlation is likely the cause. What's odd to me is that folks are chase baffling leaks and condemning the cowling but not focusing on what's causing the heat.

I would email Mr. Bush. I would also talk to the folks at Marvel Schebler. I'm not saying there's anything wrong with your plane, but maybe you can improve your operating temps and set a new bar for how optimally these engines can be run.

This is an excerpt from a column written decades ago by John Deakin, a man who's writings I've read religiously: "I will also repeat from the previous column, YOU MUST BE GETTING FULL REDLINE FUEL FLOW at full takeoff power AT SEA LEVEL! In truth, the factory redlines are often a bit on the low side, and flows should be tweaked up just a bit. Even a half-gallon per hour makes a BIG difference in CHTs during climb.

 

As a low altitude vfr east coaster, I've never leaned in climb or peaked #3 or #4 in cruise (the two that alternately show the highest CHT/EGT in climb).  Both temps in cruise are just fine and #2 or #1 peak much earlier, and I run ROP obviously.  Yet these two EGTs stay <1300 consistently in climb.  It surprises me to think that #3 or 4 are running leanest in climb but not cruise, but the correlation between high CHT and high EGT for #3/#4 does indeed support this conclusion.  What really baffles me is that when one runs hot (430ish CHT, 1400ish EGT) at WOT, the other runs cool, like #1 and #2.   Like there's something stochastic about the fuel distribution between those two cylinders from takeoff to takeoff.

Maybe fuel flow adjustment at the carb level is a key factor, as you suggest, in the hot C models.  Yet I hadn't considered it until I got the fancy monitor, since conventional thinking dictates that #3 should be hottest based on it's position in the baffle alone.   BTW I took off on basically a standard day at sea level last week in Cape May, and FF ran  17.3-17.6, which is a bit lower than the book value of 18.4.   With a carb, these adjustments seem like a fine line between not rich enough at WOT and  too rich at low rpm (I'm pretty good at fouling my plugs already).

Anyway, thanks for your input-  I'll keep digging for info, collect a bit more engine data, and post back along with the graphs from the JPI.  

[DXB]

 

Dev - how far down on the exhaust pipes are probe installed?

 

I'll measure next time I'm at the hangar...

[M20F]

With a carb, these adjustments seem like a fine between not rich enough at WOT and  too rich at low rpm (I'm pretty good at fouling my plugs already).

It is the same with fuel injection and they all run too rich.  You want to adjust so you get the fuel flow at full power,  temp, condition, etc as per the book like Ross is talking about.  You then need to lean in phases of operation (including taxi) to offset.

Gas is the #1 coolant for a cylinder if it isn't getting enough it is going to run hot.  

[Shadrach]

There are some internal engine differences that may affect cooling.  The 200hp engines have piston oilers that squirt oil on the bottom of the piston to help with cooling.  The angle valve cylinders are heavier and seem to have more cooling fins. I think I also remember reading the valves are larger also.  The C and E cooling may not be a simple comparison.

 You have an angle valve just as I do. If the piston oilers are carrying away that much heat, why do I struggle to get oil temp into the 200s in the summer and need to totally block the cooler in winter to get more than 170?  Where's the oil temp run on your F.  Do those of you with C's have trouble getting oil up to temp? Do you think that Dev's WOT full rich EGT of 1400+ is normal and healthy?

[N601RX]

That is also another difference in the two. The oil cooler on a parallel valve engine is a single pass while the angle valve engines use a dual pass.