• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

Timing and CHT relationship ?

cgoldy

cgoldy

Registered User
Moogerah Queensland Australia
I have an aerosport O-375 with one standard mag set at 26 deg and one e- mag set at 34 deg as advised. I have always been battling high CHT's and have done a lot of work to ensure that all the baffling is ok. Decided to run on the standard mag only the other day and hey presto - 20 deg temp drop. Switch to the emag and up the temp goes up again. So I disconnected the map tube to the emag (this restricts the timing to 26 deg to match the standard mag) Seems like I have fixed the problem but I am not certain I understand the logic. Also when switching to the mag only, when the cht dropped, the egt rose?

Can any one explain to me the relationship between timing and CHT's *and egt's.

Also, any advice as to what to do now. Just leave the map tube disconnected ?
 
What temp(s) is/are condsiered normal for the engine? Timing is a big factor for CHT.

High EGT can be from incomplete combustion i.e. 1 mag. The flame is "MORE" live during exhaust stoke (more so than 2 mags).
 
Last edited:
Yep.. your CHT went down because the fuel isn't getting it's burn done in the cylinder.. and the EGT went up because the fuel is now burning in the pipe at the probe area. First sign of losing a mag in flight!
 
I have the same set up, 1 mag and 1 E-Mag in an 0-320 with 9.5 to 1 pistons. I was running high CHTs until I started running lean of peak. Now they are all well under 400, like 340 to 370. In a long hard climb I'll run rich to keep it cool, but in cruise I ease the red knob out, way out. Try it you might like it.
 
Thanks. That all makes sense now. What are your thoughts on the mags set at different timing?

Looks like I should return to the original settings and look elsewhere for the problem
 
You are not the only one running hot with a modified engine. I suspect a bunch more guys are in the same boat as you but they are not fessing up to it right now. An engine makes power and heat. More power from the same engine means more heat. We are hotrodding these engines and getting more power but also more heat. Basic physics. Unfortunately we are not going 200 MPH like the RV boys so we are struggling with cooling issues. Look at all the work done on the Carbon Cub 0-340. It has a full blown plenum and still pushes the edges of acceptable CHT's. It is a known fact that electronic ignition gets a better burn/flame and thus it also creates higher CHT and EGT. The websites for Pmags and Lightspeed tell you to expect a 15 to 20 degree rise in CHT from std mags.
I don't mean to sound crass and I certainly feel for your situation but I too had CHT problems with my Lycon hotrodded 0-320. This is an area I think we need to be open and honest about until we figure out how to deal with it. But no one with a hotrodded motor wants to admit that maybe it is not so great after all.

Just my opinion

Bill
 
If you are running 9.5 : 1 pistons, the timing needs to come back to 20 0r 22 deg as the flame propagation is lot faster, or just time it WOT for max rpm on both mags
 
I would hook the map tube up, go up and lean it until its rough, go in 1//4 turn and wait about 5 minutes and see what happens. I'm assuming you have a 4 position CHT instrument. Give us a report

Tim
 
I question the advice of timing one ignition at 34 and the other at 26. The fire gets lit at 34 so by the time the 26 sparks the fire has been burning for 8 degrees. This is telling me that the 26 ignition is just dead weight which is acting as a backup in case the 34 fails. In my mind the engine thinks that it is operating on one single ignition, and as such is providing the appropriate temperatures. Maybe Fedex Lou will pipe in here. He is operating dual E-mags and as I understand it, he thinks that they are great.

I would suggest that Colin replace the mag with a P-mag. The P-mag will generate it's own power. Only needs some electricity, as little as 9v, for starting.
 
I have two pmags on my o360 in the RV and have had no problems and it now runs smooth as silk. I think I went a bit conservative with the cub knowing I was going to go bush allot.

I can't get my head around having the engine with different timing between the mags.

Roger - The engine is low compression 8.5:1

Bill - can't argue with your comments.
 
Interesting thread. I run 2 Emag P models. My 0360 has 9.5 to 1 pistons and a LEES exhaust system. I also have a Dynon EMS with all the probes. I immediately noticed an increase of 15-25F on my CHT's (pushing 400-415F in cruise). As stated, that is to be expected when you create a bigger explosion in each cylinder with advanced timing/firing. I also had an increase in oil temp of 10-20F (205-215F with 80F OAT).

Thru trial and error, and listening to these forums, I brought the temps down to 360-375F and 175-190F by the following:
Replaced the cowl baffle seal (http://www.aircraftspruce.com/catalog/appages/baffelseal3108.php) and plugged every leak I could find. I also sealed the starter ring gear (like my RV-6) and the gap between cylinder fins. I started running Camguard and Phillips 20-50XC. I have a lean mode on my EMS and always run Peak or slightly LOP. If I run more than +20F ROP it increases the CHT's by 10-15F. The biggest change came when I replaced the cowl seal with the silicone one's from Spruce.

Best of all was the reduction in fuel flow to 6.8-7.2 gph at 2480 rpm. My prop is a 8443 and TAS is 98-102 mph. Since I have a MPG readout on the EMS I experimented with best power settings....I know I could run 20-30F leaner of peak than I do, but the speed drops off and my range/mpg suffers. Zero wind mpg for me is 13.5-15.0 depending on OAT, etc. Smooth air helps a lot!

Hope this helps.

Lou
 
FdxLou said:
Interesting thread. I run 2 Emag P models. My 0360 has 9.5 to 1 pistons and a LEES exhaust system. I also have a Dynon EMS with all the probes. I immediately noticed an increase of 15-25F on my CHT's (pushing 400-415F in cruise). As stated, that is to be expected when you create a bigger explosion in each cylinder with advanced timing/firing. I also had an increase in oil temp of 10-20F (205-215F with 80F OAT).

Thru trial and error, and listening to these forums, I brought the temps down to 360-375F and 175-190F by the following:
Replaced the cowl baffle seal (http://www.aircraftspruce.com/catalog/appages/baffelseal3108.php) and plugged every leak I could find. I also sealed the starter ring gear (like my RV-6) and the gap between cylinder fins. I started running Camguard and Phillips 20-50XC. I have a lean mode on my EMS and always run Peak or slightly LOP. If I run more than +20F ROP it increases the CHT's by 10-15F. The biggest change came when I replaced the cowl seal with the silicone one's from Spruce.

Best of all was the reduction in fuel flow to 6.8-7.2 gph at 2480 rpm. My prop is a 8443 and TAS is 98-102 mph. Since I have a MPG readout on the EMS I experimented with best power settings....I know I could run 20-30F leaner of peak than I do, but the speed drops off and my range/mpg suffers. Zero wind mpg for me is 13.5-15.0 depending on OAT, etc. Smooth air helps a lot!

Hope this helps.

Lou
Click to expand...

I assume these are strictly cruise numbers. What power setting/fuel flow/cht are using for climbing? Thanks.
 
Dave

At T/O I flow 18.5-19 gph. I adjust FF to maintain 150F ROP (about 1250-1300F) during climb. Depending on conditions my hottest CYL is either 2 or 4. FF is about 15gph down low and usually CHT's don't go above 400-410 even with OAT of 80F+. I try to hold 70 IAS unless I am real heavy (2300#) and the climb is prolonged. My MA4-5 is jetted very rich so I can always enrich (richen?) for cooling if needed and pitch for 75 IAS.
My climbs are at 75-80% power initially....that yields 2500/26.5". With high MAP settings the Pmags are retarded to under 25 degs to prevent detonation. Once I set cruise power they slowly advance to 32-34 deg. Over a 2-3 minute time I watch the FF go down from 8+ gph to low 7's. They are magic! The fuel savings paid for them in about 280 hours....less than a year. They have been on for almost 900 hours and have been trouble free.

Lou
 
cgoldy, I am currently building from a Javron kit and also considering the O375 from Aerosport. I was also concerned with high temps so in discussing it with Bart he said that on Cubs they have been using oil nozzles to squirt the pistons and going with a larger oil cooler. Does yours have the squirters? Will I just be transferring the problem to high oil temps?

Thanks,
Dave
 
Dave,

I haven't heard of an oil squirter! I'll ask and let you know. My oil temps seep pretty good if I keep her roped up. Only been over 200 once and that was because the oil was low
 
The materials you are using for this engine were designed for air cooled, low compression, low RPM, and low heat circulation applications. You may need to discuss water cooled cylinder jackets etc. with the engineers for this engine.

Power comes from heat differential. Heat in then heat out. If to much heat stays in the differential is decreased, therefore less HP.
 
You must log in or register to reply here.

Similar threads

W
Hot number four cylinder
Replies
12
Views
4K
skywagon8a
skywagon8a
tcraft128
Pmag issue at New Holstein
Replies
5
Views
3K
SteveE
SteveE
A
EGT Temp and Mag Question
Replies
1
Views
1K
180Marty
180Marty
C
New Titan 340 Engine Break in - High CHT's
2 3
Replies
72
Views
11K
stewartb
S
W
0375 cht
Replies
27
Views
7K
jgerard
jgerard
Back
Top