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CHT numbers in the 14

Nova RV

Well Known Member
For the guys already flying, are any of you having high CHT issues? Yesterday was about 59 degrees OAT and I never saw CHT numbers over 300, mostly mid-high 200s (all cylinders pretty consistently close). I'm not complaining but my tech helpers who both have 7s and high CHT issues thought I must have some reading errors to be that low and I don't recall anyone with a 14 posting about high CHT issues. I was flying close to WOT and full rich as these were the first flights. Can I solicit some real world CHT numbers from you guys please?
 
Just started flying

Chris, OAT was 64 degrees F when i flew last Thursday and i saw CHTs in the 350s on 3&4, and 370s on 1&2. Running hard to seat valves, leaned to 12gph at 78% power. I?m at six hours and consistently seeing temps in the 300s.
 
What temp do you guys get for the oil, if I understand it correctly, IO390 runs cooler on CHT but hotter on oil temp.
 
What temp do you guys get for the oil, if I understand it correctly, IO390 runs cooler on CHT but hotter on oil temp.

I consistently get mid to high 180's in the cruise for oil. That doesn't seem to change much regardless of OAT. In the climb oil temp does get up to 210 sometimes but I try to avoid that. The worst scenario for oil temps is in the circuit on hot days. CHT's are never a problem.
 
What temp do you guys get for the oil, if I understand it correctly, IO390 runs cooler on CHT but hotter on oil temp.

This is my experience, mostly 300 and below in cruise. In the summer on a hot day I can get as high as 350-375 during climb, but then they come down to below 325.

I have to watch the oil temps on climb in the summer. Not really a problem but in the summer, cruise oil temps between 200 and 210 are normal for me. As the ambient air during the winter gets colder my oil temps in cruise come down into the 180's.
 
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Oil temps

My oil temps during the first six hours of break in have been in the 185-200 range. I have not done any sustained climbs, just 3,000 feet, then running hard. Touched 200 degrees at 78% power with 64F OAT.
 
Similar results to others - cruise CHTs are around 300 (couple under, couple just over). At higher altitudes (OATs 30-50), all are 280-290. On high power climbs I might hit 350 - have never seen a 400 temp ever. On a cross country winter flight with -5?F OAT, CHTs fell to 200 and I had to run rich of peak to get temps up.
Oil temps run higher as mentioned - similar results with 200-210? in high power settings, but 220? is the highest I?ve seen. One nice side benefit is the engine really warms up fast after start. Unless it?s winter, I never need to warm up - 100? oil after a short taxi.
 
Thanks guys, I will get some more data and post it tomorrow. Plesase keep sharing anyone who is currently flying. This would be important info for the next guys getting ready to fly as far as what temps seem correct for the 14
 
Seat those valves

Chris, I would consider leaning out a bit to get things hotter on a new engine to seat those valves properly.
 
I flew with a guy in his RV-14 in Michigan. His CHT?s got over 300 in the climb, maybe as high as 350 on one or two, but in cruise at least one or two were under 300. I couldn?t believe it.

In an RV-7A with a 390 that just started flying, the highest CHT I?ve seen is 394, and Cruise is around 350. Oil temp stays above 200 until the descent. I?ve seen as high as 214.
 
RV14 CHT and Oil temperatures

For the purposes of this thread I elected to post only ROP (Rich of Peak) data at or above 70% power (worst case). As you can see the RV-14 cooling system leaves significant margin for CHT cooling. Oil temperature is what I find more limiting, but still quite acceptable. I have eventual plans for a cowl flap and this data shows careful placement of the oil cooler exit in an area of low pressure will be necessary.

This data was collected over 16 months and 230 hours of flight time. THE AREAS CIRCLED IN YELLOW ARE DURING ENGINE BREAK IN.

CONDITIONS:
Percent Power between 70 and 75%
Stabilized in cruise flight at 100ROP for 2 to 7 minutes.
Altitude various but always high enough to be WOT.

NOTE: Timing in this data varies from 20 to 24 BTDC accounting for some temperature variations. 23BTDC was the best condition for speed; however, it did increase the temperatures. The breakin temperatures in the yellow circles are all at 20BTDC.

oJo.jpg
 
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I don't think you have anything to worry about, Chris. My RV14 CHTs are significantly better than my IO-540 in the RV-10. They're lower than expected. The engine gets very good cooling. I just added an oil cooler throttle valve too, because my oil temps get too low in the cold weather.
 
Hi Jesse. Actually the temps rarely get over 320 during climb at 100 knots on a hot day with 300 in cruise with oil temps around 200. Autumn temps now are running about 270 in cruise and oil temps are 190. That's a OAT of 33 F.
 
Marvin was the only respondent to note ignition timing, a very significant CHT factor.
 
Ignition timing is, of course, important. However, for the 390 (in my case XP-400) it seems that CHT is less of an indicator. I have dual PMags and I have run my engine timed 20? BTDC., 25? BTDC, jumper in and jumper out (even more advanced) with very little change in observed CHTs. In discussions with Superior, I believe the extended stroke of this engine opens the sweet spot and makes it less sensitive to timing changes.
 
Ignition timing is, of course, important. However, for the 390 (in my case XP-400) it seems that CHT is less of an indicator. I have dual PMags and I have run my engine timed 20? BTDC., 25? BTDC, jumper in and jumper out (even more advanced) with very little change in observed CHTs. In discussions with Superior, I believe the extended stroke of this engine opens the sweet spot and makes it less sensitive to timing changes.

Don't know about a sweet spot, but FWIW, the 390 has the same stroke as the 360.

Care to quantify "very little change"? Last check I made said running 20~30 LOP results in approximately 1.6 degrees F per degree of advance, which matches Nigel's data for his parallel valve. I would expect 2.5 degrees per degree running ROP.
 
CHT as a function of ignition advance

This is for 75% power at 100ROP and constant OAT. I stopped testing at 25BTDC because temperature continued to increase and speed decreased indicating I had exceeded a useful advance. Speed peaked at 23BTDC.

1zmjx37.jpg
 
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This is for 75% power at 100ROP and constant OAT. I stopped testing at 25BTDC because temperature continued to increase and speed decreased indicating I had exceeded a useful advance. Speed peaked at 23BTDC.

1zmjx37.jpg
A similar data display at 20 degrees or so LOP would be appreciated.

Carl
 
CHT LOP data

Hello Carl,
I do have LOP data. In fact, I have too much. This is my first engine which could run LOP so I tested way too many variables to understand the effects. I only post data that has been repeated at least three times. That was easy for ROP because I did everything at +100. For LOP I tested -25, -50, -75, -100, etc... I focused more on speed and fuel flow since CHT was always lower than the ROP number and my goal is to create a cowl flap; that exit dimension is controlled by the ROP temps.

A summary would be that 25LOP CHTs increase by less than 2 degrees per degree of ignition advance.
 
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It looks like there are differences between the original (Lycoming) and the clone (Superior). The XP400 is stroked an additional 0.25?. Whether or not that is material is beyond my pay grade.
 
It looks like there are differences between the original (Lycoming) and the clone (Superior). The XP400 is stroked an additional 0.25?. Whether or not that is material is beyond my pay grade.

Yeah, that's a Superior-only crank, currently out of production. It was used in the 382 and 400.

I doubt additional stroke changes the CHT vs advance relationship in any meaningful way.
 
These were my numbers yesterday at 2500 feet and OAT 61F running 24" and 2450rpm. IO390 and 2- PMAGS timed at 20 degrees.

Full rich oil temp 189
#1 235
#2 196
#3 231
#4 233

leaned to about 20 degrees rich of max EGT oil temp 191

#1 259
#2 220
#3 252
#4 251
 
Am I wrong or does the data showing excessively low CHTs scream of too much cooling drag? Is this opportunity to clean up the RV-14 cowl inlet/outlet to gain a little speed?

Carl
 
Carl,

Yes they do seem to be very low. I started this thread because of it and also because I noticed there were no posts that I could find about high CHT issues in a 14. Based on the posts here it seems to not be an issue but I agree mine seem very low and I wanted some other data than mine before I start pulling things apart to run some tests. My setup is the stock CHT thermocouples that come in the Lycoming kit from Garmin, I have the correct thermocouple wire from the sensors to the GEA24 pins and no dissimilar metals connectors or solder in between. When I was assembling, I did some tests using the stock sensors and different wire from the sensor to the GEA24 unit and did get some interesting errors vs. OAT when I used different (non thermocouple) wire.
 
At 85-95deg F (Alabama Humidity) between 4500-5500 mine are consistently 340-360 at 85%, 320-330 at 75% but I generally lean out a bit to bring them back up to 340-360. Oil temps started at around 225 but as the hours went by the settled to around 185.

The manual states:

For maximum service life, the Cylinder Head Temperature (CHT) must be maintained below 435ºF (224ºC) during performance cruise operation and below 400ºF (205ºC) for economy cruise powers.

But doesn't really give an optimal operating range.

For oil:

The maximum permissible oil temperature is 235°F. (113°C.). For maximum engine life, maintain desired oil temperature is 180°F (82.22°C).

As a noob, I'm always looking for advice on how to manage my engine.
 
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Just wondering what folks are getting for their top speed on their 14/14A.

My numbers so far has been encouraging... it has been cooler weather here so I lucked out. During the engine break-in, the two hours of full power, I was seeing 340-350 CHT and 204 oil temp. Yesterday, on my 6th hour of flight already seeing lower oil temp and CHT.
 
Just to update this for anyone collecting data, yesterday I did a boiling water test on all of the CHT probes and found #2 to be reading 20 degrees low (10% error) and the rest read 209-215 degrees (cycling around 212). This low #2 seems to corroborate the data from earlier with #2 always being lower. I also pulled all of the spark plugs and #2 were no different looking from the others so I'm sure it's firing correctly and that the one CHT probe is just off.
As to why the CHT numbers seem low from some others, no idea really. One difference from stock is that I have a Vetterman exhaust (4 into 2) which could run cooler or the exhaust opening at the rear of the cowling is larger than stock because of the extra cut outs to accommodate the dual pipes. One other difference is that I had the exhaust ceramic coated which could make a difference temp wise but I really have no way to claim this without any before/after data.
One interesting note is that my friend has a nearly identical setup in his 14A (Thunderbolt, Whirlwind prop and a ceramic coated exhaust) but his exhaust is stock and his CHT numbers are 30+ degrees higher than mine.
 
As to why the CHT numbers seem low from some others, no idea really. One difference from stock is that I have a Vetterman exhaust (4 into 2) which could run cooler or the exhaust opening at the rear of the cowling is larger than stock because of the extra cut outs to accommodate the dual pipes.

That explains a lot.

I haven't seen a Vetterman installation on a 14 but if additional openings are added to the cowl, an increase in cooling flow would be expected.
That alone might make a Vetterman exhaust not a good choice unless the builder is willing to do other experimenting to modify the stock cooling exit.
 
Verterman 4 in 2 on Superior XP400 - the cutouts don?t have to be very dramatic. However, obviously the entire tunnel is outflow.
2psiw7t.jpg

I have also since added small deflector extensions trimmed almost parallel to the airflow.
 
That explains a lot.

I haven't seen a Vetterman installation on a 14 but if additional openings are added to the cowl, an increase in cooling flow would be expected.
That alone might make a Vetterman exhaust not a good choice unless the builder is willing to do other experimenting to modify the stock cooling exit.

Scott, I'm not questioning your analysis but how are lower CHTs bad unless they are so low the cylinders can't "expand" properly and not allow it to break in properly or cause increased wear? Lower temps within reason was always told to me as being a good or better thing.

My cut outs are similar to Keith's although slightly larger.

Thanks!
 
Scott, I'm not questioning your analysis but how are lower CHTs bad unless they are so low the cylinders can't "expand" properly and not allow it to break in properly or cause increased wear? Lower temps within reason was always told to me as being a good or better thing.

My cut outs are similar to Keith's although slightly larger.

Thanks!

Yes, you can run too cool. However, I have no idea what is too cool on a lyc. There is a reason your water cooled engine has a thermostat. If your logic applied, a thermostat would not be necessary, just let it get as cool as it can. Automotive thermostats were put in place decades ago to keep temps up, not down.

Power is a function of heat. If the head is allowed to get too cool, you will unnecessarily lose combustion energy into the head instead of pushing the piston down. Engines are typically designed for an optimum level of heat loss through the head and ultimately optimum running head temps. There are other negative effects from running too cool, as well. CHTs are an indication of the balance between combustion temps, including combustion frequency and heat transfer from the head.

Ring seating has nothing to do with CHTs, nor does cylinder expansion. They are tied to cylinder wall temperature. The heads are aluminum and the cyl walls are steel. Very different heat diffusion rates. The cylinders also have different cooling fin design. I would not necessarily expect the barrel temps to follow a linear correlation with the heads and doubt that they do. However, I admittedly have no idea what the relationship looks like.

Larry
 
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From memory......Lycoming publish a number well below 200dF and TCM 225dF.

Interesting that TCM with their water cooled engine (a jacketed version of their normal engines) set the temp at 239.
 
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From memory......Lycoming publish a number well below 200dF and TCM 225dF.

Interesting that TCM with their water cooled engine (a jacketed version of their normal engines) set the temp at 225.

I found this in the IO 390 operation and installation manual, P.18

For maximum service life of the engine maintain cylinder head temperatures
between 150°F. and 435°F. during continuous operation.


Thanks for the reminder to go back to the manual for guidance !
 
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Wanted to post a conclusion here since I started this discussion. Bottom line is don't buy unknown brand thermocouple wire that claims to have the same accuracy as Omega or other quality types typically sold by good avionics shops. Once I replaced all of the thermocouple wiring the values changed considerably.

The wire became the focus once I did some more testing and found that boiling water would show as 192 degrees max on the cylinder with the most error (#2). I bought some replacement wire from Stein Air and rewired that sensor and found it to now read within a degree or 2 so all of the CHT and EGT wires were replaced and all are reading higher but in line with everyone else who have posted numbers for their -14.
 
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