What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

High CHT

P

PH-SCP

Well Known Member
Hi guys,

I am flying a RV-9 with a Lycoming O-320-D2J, James holy cowl, one magneto and one P-Mag, burning Avgas 100LL. In the cruise I am seeing CHT's between 370 and 400F, more so during the climb. Rather unhappy about that. I heard a story that changing the timing on the ingnition may improve and even dramiatically improve CHT's but I am far from an engine expert.
Any first thoughts on a way of lowering the CHT's ??

egt_cht_temps.jpg
 
When you installed that PMag, do you remember if you used the A curve or B curve (set by either including or excluding a jumper in the connector)?
 
If the engine is not broke in it will have higher temps.

I have dual P-mags and a (broke in) o-320 and I get over 400 on take off but usually in the 350 to 360 in cruise at 2350 rpm. P-mags will raise temps. Next flight, do a mag check at cruise and watch the CHT on the magneto and then the P-mag. If CHT's were OK on the magneto, but went up significantly on the P-mag, try timing it 4 or 5 degrees AFTER top dead center. Each tooth on the flywheel is about 2.4 degrees so about 2 teeth after top dead center. See if that helps.

Another issue can be a lean carb. My carb flows up to 12 gph at full throttle and contributes to higher CHT on take off. I just bought a new carb that flows at 15 gph at full throttle and will offer more fuel cooling on take off, but haven't installed yet so I can't offer data on the results.
 
Yes, ignition timing can absolutely affect the CHTs. But that's just one part of the equation. I don't want to appear condescending, as I'm having to make some assumptions based on the way the question was submitted. But my suggestion would be to begin by learning more on the basics of aircraft engine cooling. There are some very good webinars on high CHTs, but there are many other resources available, including YouTube videos, books, articles in Kitplanes and Sport Aviation, etc. Mike Busch has several articles and webinars on this subject, as it apparently affects a lot of aircraft owners. The subject has been covered in quite a few posts on this forum as well.

Just to get you started and assuming your engine is mechanically sound, there are three main areas on which to focus regarding high CHTs: 1) baffles, 2) fuel delivery, and 3) engine timing. Also, as stated in some recent similar posts, those temperatures aren't necessarily unacceptable. However, they could most likely be lowered with some modifications.
 
while those temps aren’t necessarily out of line, it looks like 1 & 3 could use some work. I would bet it is more a question of baffling than timing…
 
Check the rod between the bottom of the #1 and #3 baffles that holds them against the cylinders to make sure it hasn’t broken before making any changes.
 
georgemohr said:
When you installed that PMag, do you remember if you used the A curve or B curve (set by either including or excluding a jumper in the connector)?
Click to expand...
Hi George,
I did not build the pane myself but bought it from a builder in Florida (ex N9912X) but I will check and look at your suggestion.
Thanks a lot.
 
RV6_OKLA said:
If the engine is not broke in it will have higher temps.

I have dual P-mags and a (broke in) o-320 and I get over 400 on take off but usually in the 350 to 360 in cruise at 2350 rpm. P-mags will raise temps. Next flight, do a mag check at cruise and watch the CHT on the magneto and then the P-mag. If CHT's were OK on the magneto, but went up significantly on the P-mag, try timing it 4 or 5 degrees AFTER top dead center. Each tooth on the flywheel is about 2.4 degrees so about 2 teeth after top dead center. See if that helps.

Another issue can be a lean carb. My carb flows up to 12 gph at full throttle and contributes to higher CHT on take off. I just bought a new carb that flows at 15 gph at full throttle and will offer more fuel cooling on take off, but haven't installed yet so I can't offer data on the results.
Click to expand...
Thanks a lot !
 
D-Dubya said:
Yes, ignition timing can absolutely affect the CHTs. But that's just one part of the equation. I don't want to appear condescending, as I'm having to make some assumptions based on the way the question was submitted. But my suggestion would be to begin by learning more on the basics of aircraft engine cooling. There are some very good webinars on high CHTs, but there are many other resources available, including YouTube videos, books, articles in Kitplanes and Sport Aviation, etc. Mike Busch has several articles and webinars on this subject, as it apparently affects a lot of aircraft owners. The subject has been covered in quite a few posts on this forum as well.

Just to get you started and assuming your engine is mechanically sound, there are three main areas on which to focus regarding high CHTs: 1) baffles, 2) fuel delivery, and 3) engine timing. Also, as stated in some recent similar posts, those temperatures aren't necessarily unacceptable. However, they could most likely be lowered with some modifications.
Click to expand...
Thanks a lot !
 
D-Dubya said:
those temperatures aren't necessarily unacceptable.
Click to expand...
rocketman1988 said:
while those temps aren’t necessarily out of line
Click to expand...
No qualifiers necessary. These temps are perfectly fine, according to Lycoming and to Mike Busch, who is more conservative than Lycoming. (If I'm remembering a Vic Syracuse video correctly, he'd also be fine with these temps.) Busch places them toward the bottom of a conservative "yellow arc" running from 400-420, for what that's worth, but no data or authoritative source suggests there is any reason to do anything here. I mean, tinkering is what we do, so by all means have at it, but this engine is running fine.
 
In addition to everything said above, is there any air dam in front of 1 & 2? If no air dam is present in front of #2, is there an air bypass? Added one to our -6 last week and climb CHT’s dropped almost 40 degrees on that cylinder. I’ll post a link to that thread if I can figure it out on my phone.
 
Re set the PMAG at 2-3 degrees past TDC and not at TDC. Te=hen use the least aggressive curve. Climb out at around 115Knots or so.

report back.
 
You must log in or register to reply here.
Back
Top