[Coryb]

I fly an RV-9 with a CS prop, IO-320. On my last condition inspection my Slick Mags needed to be rebuilt so I decided to install a Surelfy EI on the left side. Since the install my CHT temps have gone up at least 20 degrees on average. At cruise LOP 10,000ft I'm seeing temps just under 400. Cylinder #3 is the hottest and was before the install. My next step will be to make sure the timing of both the Surefly and the Mag are where they need to be but I want to know if anyone has any other thoughts. I have had the plane for about 2 years. It has always ran hot on TO in hot weather. (up 415 but can be controlled by leveling off). I will include a picture of the underside of my upper cowling. You can see where the baffle is rubbing. I wonder if any of the areas where I have placed arrow could be causing enough air leaks to effect the temps. Thanks for any ideas and thoughts.

 

[BruceW]

Reduce your advance.

 

[Mike S]

Reduce your advance.

YEP.

EI setups tend to induce heating due to the timing advance they offer.

 

[Richard Connell]

Definitely double check the timing as above.
However… if the timing is ok, then 400f (or even 380) LOP at 10k sounds too hot. What sort of temps do you see ROP?.
I’d definitely be looking at your cooling. Baffle seals. Intake ramps. Inter cylinder baffles etc. Theres a few good threads on cooling.
Even in the middle of summer I’d be expecting no more 350F while LOP up high with EI.
TBH if you have to level off to cool as you climb you probably do have significant room for cooling improvements.

 

[kiwipete]

Cowl ramps

Cory

Check the cowl inlet ramp sealing. It looks like air could pass underneath the ramps if one end is sealed on the ramp (outside end) and the other beside the ramp. Blocking the underside of the ramp will stop this.
Looking at the cowl it appears to not show a good seal in this area.

Regards Peter

 

[RV10inOz]

I have been on about this for years with PMAGS and others. I note these days they all recommend reducing the timing a couple fo degrees.

On the Surefly from memory you can select via dip switches a lesser advance. That may be the easier way to go. Otherwise when doing a setup pul the prop through a further 2-3 degrees past top dead centre and "trick" the EI into thinking that is TDC.

The reason for the higher CHT is a much higher "peak pressure". Even though the static timing is say 25 or 22 degrees as called for on the engine data plate. The reason you get the higher pressure is because the spark plug fires 2-3 degrees earlier with the EI compared to a magneto, thus the peak pressure is higher. You are not generating any more power and in some circumstances less. We have seen this on the GAMI engine test stand where they have the ability to accurate measure the point in time when the plug fires. On a Chieftain engine the difference is a whopping 3-6 degrees. The magneto has a bunch of lag in it so the actual plug firing is later than the static setup number.

That will restore normality in your world.

 

[lr172]

I have my doubts about timing, but definately check. At 10K cruise in my RV10, I will be near WOT and 2400 with a FF of 10.5 GPH and advance around 32+*. I see CHTs around 350*. That is probably 80* LOP. Even if you are richer than that, the extra timing should not be causing 400* CHTs. If the overall base timing was high on the surefly's, you should be seeing significantly higher CHTs in TO and ROP climb phases. If the base timing is not off, it seems quite unlikely that the advance table is causing higher CHTs in LOP cruise.

The weak point with these systems is an inability to distinguish LOP and ROP. Usually the problem is later stages of climb. At 8K, your system is getting a decent amount of advance above the base timing (table is based upon MAP, yet MAP will drop at altitude even if ROP), yet you are still ROP at high power. This causes the CHTs to rise a good amount. Once you level off and go LOP, the extra advance now works well with the lean setting and temps go down. If this is not happening to you, I suspect the new surefly advance is not the cause of the high CHTs in LOP cruise (Here, the extra advance is now using more heat for work instead of blowing it out the exhaust, causing the rise in combustion temps). Yes, the extra advance will add some CHT in LOP cruise, but nowhere near the 400 level unless you have other cooling issues.

Another challenge with these systems are the fixed adv table. Optimum adv is based in part on mixture. Richer wants less advance and leaner wants more advance for optimum conversion of combustion energy to work. If the adv table is fixed, you can adjust mixture to reach the optimum point.

Larry

 

[DanH]

I fly an RV-9 with a CS prop, IO-320. On my last condition inspection my Slick Mags needed to be rebuilt so I decided to install a Surelfy EI on the left side. Since the install my CHT temps have gone up at least 20 degrees on average.

I imagine the DIP switches are set for timing advance. Easy experiment; set them for fixed timing to match your remaining magneto, go fly, see if the CHTs fall back into line with previous experience. The switch settings are in the instructions.

The effect of advance on CHT:

 

[Ingo Weise]

With higher advance you get higher combustion pressure and hence better effiency. The temperature rises nearly linear with pressure.
If you reduce the advance, you will give up the advantage of the electronic ignition.
It was too hot before you changed to Surefly EI. You should first solve your cooling problems, before you make any changes to the ignition timing.

 

[RV10inOz]

We have seen on the GAMI dyno, the benefits of any advance on an appropriate LOP mixture is about 27 degrees for parallel valve engines. That equates to 4-5 degrees of actual spark advance compared to a magneto.

Fix the timing on the Surefly as Dan has suggested and set between 23-25 degrees only. You will find this will work wonders.

 

[DanH]

With higher advance you get higher combustion pressure and hence better effiency. The temperature rises nearly linear with pressure.
If you reduce the advance, you will give up the advantage of the electronic ignition.

Although more advance can certainly result in higher peak combustion pressure, it does not necessarily result in better efficiency.

The goal is to adjust ignition timing so peak pressure is in the region of 10~16 degrees ATDC. If too much advance causes peak pressure to arrive early, nearer to TDC, peak pressure will be higher, but the crankshaft geometry may not result in additional torque, only higher mechanical stress.

The experimental community tends to display a significant disconnect between the LOP theory taught at APS/GAMI, and the use of EI's with extended advance schedules. The whole point of LOP operation, as taught by Braly, Deakin, Brown et al, is to delay the point of peak pressure, reducing cylinder stress and temperature. The principle is simple. It assumes fixed timing as installed on the vast majority of the certified fleet, so given that lean mixtures combust slower, the red knob becomes a timing control. Pull it out further, and peak pressure moves farther from TDC. Yes, there is some power loss. With a turbo-normalized engine, they just add some manifold pressure to recover the loss...and keep the effectively delayed timing.

Very few turbos in our world, so the trend has been to offset the slower lean combustion rate with more timing advance. There's nothing wrong in doing so, if that additional advance merely returns peak pressure to the original optimum point after TDC. However, it is very much a Goldilocks thing...it can be too little, too much, or just right. For sure, more is not necessarily better, in particular when considering factors like engine life.

Oh, and let's not conflate the benefits of electronic ignition with the benefits of advanced ignition timing. They are very different subjects. A fixed timing EI can be a wonderful thing to have.

 

[Toobuilder]

Although more advance can certainly result in higher peak combustion pressure, it does not necessarily result in better efficiency.

The goal is to adjust ignition timing so peak pressure is in the region of 10~16 degrees ATDC. If too much advance causes peak pressure to arrive early, nearer to TDC, peak pressure will be higher, but the crankshaft geometry may not result in additional torque, only higher mechanical stress.

The experimental community tends to display a significant disconnect between the LOP theory taught at APS/GAMI, and the use of EI's with extended advance schedules. The whole point of LOP operation, as taught by Braly, Deakin, Brown et al, is to delay the point of peak pressure, reducing cylinder stress and temperature. The principle is simple. It assumes fixed timing as installed on the vast majority of the certified fleet, so given that lean mixtures combust slower, the red knob becomes a timing control. Pull it out further, and peak pressure moves farther from TDC. Yes, there is some power loss. With a turbo-normalized engine, they just add some manifold pressure to recover the loss...and keep the effectively delayed timing.

Very few turbos in our world, so the trend has been to offset the slower lean combustion rate with more timing advance. There's nothing wrong in doing so, if that additional advance merely returns peak pressure to the original optimum point after TDC. However, it is very much a Goldilocks thing...it can be too little, too much, or just right. For sure, more is not necessarily better, in particular when considering factors like engine life.

Oh, and let's not conflate the benefits of electronic ignition with the benefits of advanced ignition timing. They are very different subjects. A fixed timing EI can be a wonderful thing to have.

Dan - Appreciate the informative post but I want to clarify your use of the words in the bolded section above. I have read plenty of the LOP guidance out there, including those you referenced, but I will admit that I seem to have missed that the "whole point" of LOP ops is to delay the point of peak pressure outside of the optimal crank angle relationship. We both agree that that is a RESULT of the limitations of fixed timing, but I do not think anyone is trying to purposely alter the optimum peak pressure/crank angle relationship. One can demonstrate measurable speed gains at constant fuel flow with optimized timing vs. fixed. If there was a good way to move timing to regain the optimal PCP/crank angle relationship in the certified world, they would do it.

If there is a disconnect between the Exp community and the certified world , it is only because we have the ability to adjust timing to do what they would desperately like to do - achieve that Goldilocks level of PCP/crank angle, regardless of how fat or how lean the mixture or air is. I think we are in agreement that the pressure/angle relationship is the key to mechanical output of the engine as well as longevity, regardless of altitude or mixture.

Where we in the Exp community goes "wrong" at times is when we select a product or curve that pushes the PCP too early in the crank angle and the engine just ends up fighting itself in the form of high CHT and lower power output. By definition, LOP ops is lower power and lower stress on our non turbo'd engines, but that is true even when the PCP/crank angle is "optimal". This is a capability we enjoy that the typical Bonanza driver does not, but lets make sure we do not paint a cautionary tale when it is not warranted.

"Just right" is always "just right".

 

[Mconner7]

I have the same setup on my -10. Since my recent overhaul, #6 runs close to 400 when above 60% power. I recently timed the SIM one tooth retarded on the ring gear. It dropped the temps on all cylinders 10-20*.

I just did an oil change and set the SIM to fixed timing to see if the advance was contributing. I have not had a long enough trip to know the results but all of this process was discussed with Sure Fly.

 

[RV10inOz]

Although more advance can certainly result in higher peak combustion pressure, it does not necessarily result in better efficiency.

The goal is to adjust ignition timing so peak pressure is in the region of 10~16 degrees ATDC. If too much advance causes peak pressure to arrive early, nearer to TDC, peak pressure will be higher, but the crankshaft geometry may not result in additional torque, only higher mechanical stress.

The experimental community tends to display a significant disconnect between the LOP theory taught at APS/GAMI, and the use of EI's with extended advance schedules. The whole point of LOP operation, as taught by Braly, Deakin, Brown et al, is to delay the point of peak pressure, reducing cylinder stress and temperature. The principle is simple. It assumes fixed timing as installed on the vast majority of the certified fleet, so given that lean mixtures combust slower, the red knob becomes a timing control. Pull it out further, and peak pressure moves farther from TDC. Yes, there is some power loss. With a turbo-normalized engine, they just add some manifold pressure to recover the loss...and keep the effectively delayed timing.

Very few turbos in our world, so the trend has been to offset the slower lean combustion rate with more timing advance. There's nothing wrong in doing so, if that additional advance merely returns peak pressure to the original optimum point after TDC. However, it is very much a Goldilocks thing...it can be too little, too much, or just right. For sure, more is not necessarily better, in particular when considering factors like engine life.

Oh, and let's not conflate the benefits of electronic ignition with the benefits of advanced ignition timing. They are very different subjects. A fixed timing EI can be a wonderful thing to have.

WELL SAID DanH.

The point here is with rich mixtures you want no advance, in fact spark plug firing around 22-23 degrees BTDC for the parallel valve engines is a general sweet spot. With the leaner mixtures when appropriately LOP a few degrees of advance helps greatly with keeping ThetaPP in the sweet spot. Once you go past about 27-28 it starts getting sub-optimal.

If you have an SDS system for example where a push of a button or flick of a switch can give you this small advance shift then happy days. If you have a more fixed system like a Surefly then it is best to set it up at around 22-23BTDC and if there is a MAP schedule available take the least aggressive one possible.

Thanks for the kind words Dan. Humbling.

 

[DanH]

Dan - Appreciate the informative post but I want to clarify your use of the words in the bolded section above. I have read plenty of the LOP guidance out there, including those you referenced, but I will admit that I seem to have missed that the "whole point" of LOP ops is to delay the point of peak pressure outside of the optimal crank angle relationship.

Nobody suggested a delay would move peak pressure outside of the optimal. Not me, and for sure not Braly and Deakin.

Let's look at a specific example. Review the section titled "Geometry and Physics Into the Fray":

https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/

Here are the notable illustrations:

https://s30121.pcdn.co/wp-content/uploads/1999/06/Rich-of-Peak.jpg.webp

https://s30121.pcdn.co/wp-content/uploads/1999/06/Lean-of-Peak.jpg.webp

https://s30121.pcdn.co/wp-content/uploads/1999/06/Comparison-Rich-of-Peak-vs-Lean-of-Peak.jpg.webp

 

[riobison]

I have the same setup on my -10. Since my recent overhaul, #6 runs close to 400 when above 60% power. I recently timed the SIM one tooth retarded on the ring gear. It dropped the temps on all cylinders 10-20*.

I just did an oil change and set the SIM to fixed timing to see if the advance was contributing. I have not had a long enough trip to know the results but all of this process was discussed with Sure Fly.

So, retarded the timing some where between 2.42 and 2.95 degs the cyl head temp dropped 10 to 20 degs?

That is a question I have had in the back of my mind and now it appears answered.

I will be testing this shortly as well.

Thanks
Tim

 

[Darinh]

I imagine the DIP switches are set for timing advance. Easy experiment; set them for fixed timing to match your remaining magneto, go fly, see if the CHTs fall back into line with previous experience. The switch settings are in the instructions.

The effect of advance on CHT:

I did the same thing with my Rocket (replaced the left slick with a Surefly) and with the dip switches set to the advanced timing option, my temps were all up 20-30 degrees. Once the dip switches were moved back to fixed timing, temps are back down and comparable to dual slicks as it was set up previously.

Honestly, I didn't see any performance or fuel burn differences between advanced settings and fixed. I did not perform any specific comparisons but based on the "calibrated eyeball", the differences are negligible.

 

[S. Soule]

Regarding this, "I recently timed the SIM one tooth retarded on the ring gear. It dropped the temps on all cylinders 10-20*." Do you mean that you moved the flywheel one tooth before TDC and then set your timing? Steve

 

[S. Soule]

Well, I meant "one tooth after TDC..."

 

[penguin]

Dan H, what ignition system(s) do you use and what is your static timing set to?

 

[DanH]

Dan H, what ignition system(s) do you use and what is your static timing set to?

390 angle valve, EDIS w/ MegajoltE control, mapped at 23 BTDC fixed.

Like many EI's, the static timing set point is TDC.

The system allows entry of two independent advance maps with inflight switching. I've run a variety of advance schedules. Below is the currently installed map #2, but I've found little value in it with the angle valve. The other photo is typical at 23 fixed, peak EGT cruise, going home from OSH this year with the new 380-150 tires in the breeze.
.

 

[Pittsartist]

Listen to the FCS (fly cool sh..) podcast with Skip Stewart where he is talking about his experiences having engines built with electronic ignition versus traditional mags.

Some real insights to be had - all based on extensive first hand experience (albeit with a different mission in mind). I think his summary of the differences is spot on.

 

[riobison]

Listen to the FCS (fly cool sh..) podcast with Skip Stewart where he is talking about his experiences having engines built with electronic ignition versus traditional mags.

Some real insights to be had - all based on extensive first hand experience (albeit with a different mission in mind). I think his summary of the differences is spot on.

Skip has a lot of video's, can you help us out with a link?

 

[rv8ch]

... going home from OSH this year with the new 380-150 tires in the breeze.
.

Dan, Are those numbers are without wheel pants? Or are you just noting that there is a bit more tire sticking down from the wheel pants? Thx.

 

[Coryb]

Thank you for all your responses. Since it is difficult to reach the Surefly to change the timing through the switches, I decided to look at airflow and the baffle first. I know I'm going to need to address the timing one way or another but the baffles seems to be the low hanging fruit. I used RTV to plug a couple of gaps near the intake ramps but I did not see a difference in CHT temps. I have a couple of holes in the back of the baffles. They each have plastic tubes that extend about 5 inches past the baffles. Nothing runs through them It's just a place for air to escape. I'm not sure if they are supposed to be there or not.

I also have a good size hole on one side where the engine mount is connected. I will attach photos. Should I fill any of these holes?

I know I will need to retard the timing or change my DIP switches to be fixed at some point also.

 

[DanH]

Blast tubes, doing nothing. Remove, and close the holes.

Looks like heaters at the cylinder bases. Probably some open gaps there.

The flap seals without wear marks indicate leakage.

 

[uk_figs]

Blast tubes, doing nothing. Remove, and close the holes.

Dan
I have the blast tubes pointing at the mags, followed someone's advice and been there since the build in 2008, are you saying they are not needed and I can close those holes?
Figs

 

[Coryb]

The flap seals without wear marks indicate leakage.

Here's the picture of the top cowl. Should I try to seal the gaps between the baffle material? Or do you think air is getting through over the whole top and I should replace the whole side of baffle material?

 

[DanH]

Dan
I have the blast tubes pointing at the mags, followed someone's advice and been there since the build in 2008, are you saying they are not needed and I can close those holes?
Figs

Hi Figs. The vast majority of blast tube installations don't actually cool the specified component, in particular those which sorta, kinda fart in the general direction of the device. They're just a big leak, same as a crappy baffle seal.

A blast tube leading to a dedicated shroud can actually provide some cooling, but only when the airplane is moving. Repeated measurement says the highest temperatures are reached after shutdown, with or without blast tubes. Blast tubes or not, the component then operates hot for quite some time after re-start.

You said "mags". Slicks, or something else?

 

[DanH]

Here's the picture of the top cowl. Should I try to seal the gaps between the baffle material? Or do you think air is getting through over the whole top and I should replace the whole side of baffle material?

I am reminded of the old Dear Abby adage..."Any girl can get married if she sets her sights low enough".

The ultimate goal is zero leakage. You decide how good is good enough for you.

Picture is interesting. You have a number of small leaks, as evidenced by no baffle contact with the cowl (red circles). You also have a number of smudge spots where leaks have deposited soot and dirt (blue arrows). Note some are next to obvious no-contact gaps, and others are adjacent to contact, meaning they leak only when the engine is torqued from its resting position. It suggests the seals are old and hard in that area, as they no longer dynamically follow engine movement. Note the strip of smudge on the right side of your photo. That's the left baffle seal. From the seat, prop turns clockwise, engine torques CCW, and the left seal moves away from the cowl.
.

 

[Coryb]

Dan, Thank you. This is great input. The plane is about 15 years old. I did not build it but it looks like I'm going to get some building experience starting with the baffles.

 

[uk_figs]

Hi Figs. The vast majority of blast tube installations don't actually cool the specified component, in particular those which sorta, kinda fart in the general direction of the device. They're just a big leak, same as a crappy baffle seal.

A blast tube leading to a dedicated shroud can actually provide some cooling, but only when the airplane is moving. Repeated measurement says the highest temperatures are reached after shutdown, with or without blast tubes. Blast tubes or not, the component then operates hot for quite some time after re-start.

You said "mags". Slicks, or something else?

Slicks, rebuilt at 500 hours (about 300hours ago), they have worked well for 15 years but am thinking of a Surefly before the next IRAN to replace the impulse mag. My 3 & 4 CHTs run in the 350 -370 range at cruise hence the interest in this thread.

 

[DanH]

Slicks, rebuilt at 500 hours (about 300hours ago), they have worked well for 15 years but am thinking of a Surefly before the next IRAN to replace the impulse mag. My 3 & 4 CHTs run in the 350 -370 range at cruise hence the interest in this thread.

Nobody knows if your blast tube installation is actually doing anything useful. Install temperature sensors at the coil and capacitor, fly with and without blast tubes, post the graphs.

Returning to topic, a Surefly offers eight choices for fixed timing, so you can set it just like your old mag and expect the same CHT. Surefly and Lycoming EIS (the rebranded version) instructions do not ask for a blast tube.

 

[Coryb]

I also have a blast tube in the front for the alternator. Is that something I should think about plugging? Seems like I see most RVs with it.

 

[Coryb]

Report on progress. Thanks for helping. I have spent the last few days going over air flow issues. After a tube of RTV, which included plugging the 2 blast tubes to the Mags, My climb out temps are down about 20 degrees and cruise temps 15-20. I wanted to see temp changes before I changed the timing on the Surefly. Next time out I'm going to retard the Surefly timing to 24 degrees and see what that does.

 

[Pete O Static]

I also have a blast tube in the front for the alternator. Is that something I should think about plugging? Seems like I see most RVs with it.

FWIW, My alternator kept failing. Installed a blast tube and have not had any issues since.

 

[Coryb]

the latest.

I checked the timing of the Surefly and found it to be about 1 degree advanced. I followed the instruction from the Surefly troubleshooting page and reset the timing to TDC. I used a dial indicator to determine TDC. When looking at the markings on the flywheel it looked to me to be a couple of degrees after TDC. So all in all I probably retarded the timing 3 degrees from where it was.

Results:
1) the first thing I noticed was the RPM drop on the right side (traditional mag side) went from 150 to 100. I didn't do anything to the right side.

2) On my first flight the CHT temp increase on #3 during climb out seemed to be degreed. It never went about 410.

3) At cruise it leveled off to a very acceptable 363 and stayed there for all my flying that day (about 5 hours) I thought it was fixed!

4) On my return flight 3 days later my numbers seemed to be back where they were previous to the timing change. I'll share the numbers in the table bellow.

I'm back to the drawing board. I am more convinced now that it is an airflow problem given that fact the #1 and to a lesser degree #2 are on the cool side for both flights.


Any ideas?
Friday 9/22
OAT 44
Gal/hr 4.8
CHT
#1 319
#2 353
#3 363
#4 357
EGT
#1 1367
#2 1448
#3 1325
#4 1421
OIL 166
MAP 20.3
RPM 2390
TAS 143
ALTITUDE 9,500
Baro. 30.07

Monday 9/25
OAT 43
Gal/hr 5.3
CHT
#1 314
#2 365
#3 393
#4 383
EGT
#1 1333
#2 1420
#3 1280
#4 1322
OIL 169
MAP 19.7
RPM 2300
TAS 143
ALTITUDE 11,500
Baro. 30.25

 

[Mconner7]

I have the same setup on my -10. Since my recent overhaul, #6 runs close to 400 when above 60% power. I recently timed the SIM one tooth retarded on the ring gear. It dropped the temps on all cylinders 10-20*.

I just did an oil change and set the SIM to fixed timing to see if the advance was contributing. I have not had a long enough trip to know the results but all of this process was discussed with Sure Fly.

Ok a couple of longer flights later, my CHT’s are well below 400* in any cruise power setting. I have not taken it above 11,000’ but I don’t see any significant change in fuel flow or performance without the timing advance. I will leave it in fixed timing.

 

[bjdecker]

Ok a couple of longer flights later, my CHT’s are well below 400* in any cruise power setting. I have not taken it above 11,000’ but I don’t see any significant change in fuel flow or performance without the timing advance. I will leave it in fixed timing.

If you have questions about variable ignition timing, please read the following from CAFE

https://cafe.foundation/v2/pdf_cafe_reports/ignition1.pdf
https://cafe.foundation/v2/pdf_cafe_reports/ignition2.pdf
https://cafe.foundation/v2/pdf_cafe_reports/ignition3.pdf