Looking for a fix- high CHTs on SQ2

supercub9675 said:

The 7500 ft density altitude should help cool your engine, because unless it is turbocharged, it won't be able to generate full hp. As you ascend in altitude, your engine produces less hp, right? Mike Busch (SavvyAviation) has some lectures on engine leaning-ROP-LOP etc. He says the worst cht to operate at is, I think, 40 to 50 degrees ROP. This is where the most pressure and heat are generated in a normally aspirated engine. I'm no expert, but it is quite interesting to hear what Mr. Busch has to say. https://www.youtube.com/watch?v=X-tKyiUZ3ts&t=3344s

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Re cooling effect at altitude:
Thermal conduction of air decreases with altitude, at about the same rate engine performance decreases.
Both effects are the result of fewer air molecules available for a given volume, In spite of standard temperature lapse, an engine running at sea level will experience similar CHT’s at 12,000’ - at same power setting and fuel mixture ratio. Running ROP & LOP to manage temps is another topic and does not address the underlying problem.

Engine/cooling/installation should provide for manageable temps under normal operating conditions, It’s no fun flying behind a hot engine, Ive been there, takes alot of fun out of flying.

This photo is from a Vans Aircraft website. This baffling is a good example and shows a seal behind the prop that keeps the air pressure in the pressure chamber, preventing it from escaping behind the propeller. Do you have anything like this?

https://vansairforce.com/community/showthread.php?t=141528&highlight=Prop+baffle+seal

I don't have a baffle there. I'll try that before I do my major overhaul of the lower cowling.

I have extensive front baffles that I've previously shared here. Two pictures below. Ignore the hose--I was pre-oiling the engine before first start.

This front baffle came with an 0360 universal baffle kit from vans,
maybe fab up something similar

Very interesting ideas. I never paid much attention but my nephew's SQ cowl is very different in front than the couple shown in this thread.

bcone1381 said:

This photo is from a Vans Aircraft website. This baffling is a good example and shows a seal behind the prop that keeps the air pressure in the pressure chamber, preventing it from escaping behind the propeller. Do you have anything like this?

https://vansairforce.com/community/showthread.php?t=141528&highlight=Prop+baffle+seal

View attachment 50986

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Interesting. But I think the center blocking baffeling probably needs to extend outward farther away from spinner(low pressure/exit area). I don’t think shrinking the front inlet will be a bad thing... because it already had too much air going in at outside and flowing out near propeller.... just watch water in a stream by a sand bar and how it reverses....


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another month and a half later... any more testing & data points learned??

Hi Guys,
Its been awhile since I've contributed to any of the threads on here, but I came across this particular thread and thought I would add some info and ask some questions. I have the SQ2 Engine mount and cowling and have also been fighting high CHT's since day one. I have slightly over 500 hrs on my Aero Sport 0320 B2B with duel pmags and still can not overcome the high CHT's. She sometimes runs 420 degrees plus in high AOA and low speed, and quite often #3 and #4 run over 400 degrees with #1 #2 running about 20 degrees less in cruise during the summer with temps around 75 to 80 degrees. I am constantly managing power to try to keep engine cool. As you can see below, I have tried just about everything recommended, bumped out the baffles behind both 3 and 4 cyl, built a divided plenum, changed ramp angles, added and removed air dams on 1 and 2, extended lower cowl lip to close gap at bottom of outlet, added a deflector flare for draw on lower outlet chamber, added louvers to side cowl doors, removed jump wire from pmags to eliminate timing advance, even added vortolator tape to leading edge of prop, probably a few other things I don't recall. None of what I have done so far has given any appreciable results. I am thinking about returning to the stock Cub Cowling and Engine mount which I really don't want to do if i don't have to. Has anyone come up with anything that works for the SQ2 Cowl? any new info? anyone?

still frustrated here in da Yoop.

I've been intending on updating this post - thanks for the poke.
I've gone through about every trick posted anywhere to get my CHTs below 400. Nothing worked. About a month or so ago I decided to do what some people will say is giving up and retarded my timing by 5 degrees. That made a huge change. I don't need the full 180 HP my engine will produce and my takeoff distance is still shorter than my consistent landing distance.

But Bruce Reed at Backcountry Cubs says the cowl is "just fine"--runs very cool as designed. HORSE-HOCKEY Bruce!

rotto789 said:

Hi Guys,
Its been awhile since I've contributed to any of the threads on here, but I came across this particular thread and thought I would add some info and ask some questions. I have the SQ2 Engine mount and cowling and have also been fighting high CHT's since day one. I have slightly over 500 hrs on my Aero Sport 0320 B2B with duel pmags and still can not overcome the high CHT's. She sometimes runs 420 degrees plus in high AOA and low speed, and quite often #3 and #4 run over 400 degrees with #1 #2 running about 20 degrees less in cruise during the summer with temps around 75 to 80 degrees. I am constantly managing power to try to keep engine cool. As you can see below, I have tried just about everything recommended, bumped out the baffles behind both 3 and 4 cyl, built a divided plenum, changed ramp angles, added and removed air dams on 1 and 2, extended lower cowl lip to close gap at bottom of outlet, added a deflector flare for draw on lower outlet chamber, added louvers to side cowl doors, removed jump wire from pmags to eliminate timing advance, even added vortolator tape to leading edge of prop, probably a few other things I don't recall. None of what I have done so far has given any appreciable results. I am thinking about returning to the stock Cub Cowling and Engine mount which I really don't want to do if i don't have to. Has anyone come up with anything that works for the SQ2 Cowl? any new info? anyone?

still frustrated here in da Yoop.


View attachment 58950View attachment 58949

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Did you close "restrict" the size of the cooling air outlet at the bottom of the cowl? If so, you restricted the flow of cooling air.

By removing the jump wire you advanced the timing to 39 BTC degrees. With the jumper installed the timing is only 34 BTC degrees. See page 13 https://emagair.com/wp-content/uploads/2017/08/Manual-LC114v28.pdf
Did you time the P-mags to the engine at TDC? See Page 13-14. I suggest you recheck your initial timing to TDC and reinstall the jumper.

Next, in your left picture you have blocked any cooling air from the crankcase. Why have you closed in the "air chamber" above the cylinders? Generally the cowl forms the top cover over the engine. I suggest you remove the top cover and make a rear baffle which forms a wall to the top cowl. Continue the side baffles up to meet the top cowl.

What type of fuel distribution do you use? Carburetor or fuel injection? What is your fuel flow during cruise and at full power? If you are running too little fuel flow your temperatures can be too high.

Can you post a picture of your side cowls? The amount of air they allow out of the engine helps a lot with the cooling.

How are your oil temperatures running? Normal, too high or low? Where is the cooler?

The front air inlet ramps seem to work efficiently when they are sloped up to about the center of the cylinder. At least they do on mine.

Using a sleek cowl to reduce cooling drag never made sense to me for an airplane with slats and 35" tires hanging in the breeze. I have mod-Cub friends who disagree with that, though. As a long time Cessna driver beginning to fly Cubs one of my favorite features was turning a couple of butterfly fasteners and having full access to the engine. The more tricked-out the engine, the more I appreciate easy access to inspect it.

Sky,

to answer your questions:

1: the jumper wire is actually installed, on both pmags, I just couldn't remember which way I changed it. Also, Timing is set up at TDC I reconfirmed this at last condition inspection.
2: I simply extended the tunnel at bottom of cowl in the hopes of stopping the air flow from wrapping around under the cowl and creating pressure in the otherwise low pressure area. did not make opening any smaller, this mod made no change so went back to original profile with a lip installed.
3:The chambers or divided plenum was an effort to direct the ram air down through the cylinders and not create turbulence within the plenum, this was recommended by an A&P IA here on my field, the results of the change from the original plenum you describe to the divided covered plenum i built yielded no change at all.
4: fuel distribution is via Marvel Schebler Carburetor with increased main jet size to allow more fuel for and to crate the acceptable EGT Rise. This modification did help, albeit very little, and really does not allow me to lean for peak air/fuel ratio and consumption during the summer months because of the High CHT's in other words "running full rich to help keep cyl's cool"
5: side cowling mods: I have tried the reverse scoop with flare to suck air out with no change, ran without side cowl and duct taped flare at leading edge of opening for same result "no change" currently running a hood louver from a Mazda Miata on both sides with "no change" thinking about installing cowl doors similar to stock cub for a bigger opening at sides of firewall like Ted Waltman did.
6: Oil temps with the oil cooler mounted at the back of #4 cylinder are running pretty normal for the most part, sometimes on a really hot day it will push slightly past the 200 degree mark.
7: inlet ramps are halfway up the cylinders as you recommend.

with all of this in mind, I am pretty tired of the BS and actually seriously considering installing stock cub cowl. With almost 6 years of fighting it, i'm over it!

Thank you for your input,

Rick

skywagon8a said:

Did you close "restrict" the size of the cooling air outlet at the bottom of the cowl? If so, you restricted the flow of cooling air.

By removing the jump wire you advanced the timing to 39 BTC degrees. With the jumper installed the timing is only 34 BTC degrees. See page 13 https://emagair.com/wp-content/uploads/2017/08/Manual-LC114v28.pdf
Did you time the P-mags to the engine at TDC? See Page 13-14. I suggest you recheck your initial timing to TDC and reinstall the jumper.

Next, in your left picture you have blocked any cooling air from the crankcase. Why have you closed in the "air chamber" above the cylinders? Generally the cowl forms the top cover over the engine. I suggest you remove the top cover and make a rear baffle which forms a wall to the top cowl. Continue the side baffles up to meet the top cowl.

What type of fuel distribution do you use? Carburetor or fuel injection? What is your fuel flow during cruise and at full power? If you are running too little fuel flow your temperatures can be too high.

Can you post a picture of your side cowls? The amount of air they allow out of the engine helps a lot with the cooling.

How are your oil temperatures running? Normal, too high or low? Where is the cooler?

The front air inlet ramps seem to work efficiently when they are sloped up to about the center of the cylinder. At least they do on mine.

Click to expand...

What’s your cylinders look like after 500hrs when you borescope them?

rotto789 said:

Sky,

with all of this in mind, I am pretty tired of the BS and actually seriously considering installing stock cub cowl. With almost 6 years of fighting it, i'm over it!

Thank you for your input,

Rick

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Rick, I understand your frustrations. However, before you tear it all apart for rework will you please post some pictures of the exit under the lower cowl and your side cowls with their louvers?

3 above: It is possible that restricting the space above the cylinders as you've done could create air turbulence which in itself restricts the airflow. You are looking for a large volume of air moving unrestricted. When you squeeze it in a small space it becomes restricted. Since you have tried this both ways with no difference, it appears there may be an outlet restriction.

6 above: Cooling air flowing around the crankcase and oil sump contribute to the cooling of the oil.

Just to give you an idea, My Cub has the stock -18 cowl over a IO-360B2B engine and there is no interior in the cabin. When I place my hand on the inside of the fabric just ahead of the door, it is very warm. Warm enough so I believe it actually contributes to heating the cabin. This is engine cooling air coming from the opening at the trailing edge of the side cowl. The only time I've seen CHTs over 400 is on a very hot summer day. Increasing fuel flow between 1/2 to one gph brings the temperature below 400.

last condition inspection yielded compressions in mid 70s with borescope bore and valve inspection normal. I have had to manage CYL temps with power input for almost 6 years now and the engine is holding up well. would really be nice to be able to cruise at say 2600 RPM and never worry about temps, not the case here. depending on how I pitch my ground adjustable prop I have to be very careful of power settings for Cyl temp reasons.

KevinJ said:

What’s your cylinders look like after 500hrs when you borescope them?

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Current configuration,

skywagon8a said:

Rick, I understand your frustrations. However, before you tear it all apart for rework will you please post some pictures of the exit under the lower cowl and your side cowls with their louvers?

3 above: It is possible that restricting the space above the cylinders as you've done could create air turbulence which in itself restricts the airflow. You are looking for a large volume of air moving unrestricted. When you squeeze it in a small space it becomes restricted. Since you have tried this both ways with no difference, it appears there may be an outlet restriction.

6 above: Cooling air flowing around the crankcase and oil sump contribute to the cooling of the oil.

Just to give you an idea, My Cub has the stock -18 cowl over a IO-360B2B engine and there is no interior in the cabin. When I place my hand on the inside of the fabric just ahead of the door, it is very warm. Warm enough so I believe it actually contributes to heating the cabin. This is engine cooling air coming from the opening at the trailing edge of the side cowl. The only time I've seen CHTs over 400 is on a very hot summer day. Increasing fuel flow between 1/2 to one gph brings the temperature below 400.

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0-375? Oil temps are okay? I think there’s a reason the SQ variants use angle valve 390s now.

After blowing my ring gear apart at the 2nd or 3rd start-up I keep my Pmags timed at about 4° after TDC. After the kick-back we had them at 6° after and it stayed that way until the 400 was recalled. Maybe retarding the timing is worth a try. I can switch timing curves at the panel and for my needs I can’t tell any difference so I use A.

rotto789 said:

Current configuration,

View attachment 58973

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Interesting, from here it looks as though the air will spill back into the lower cowl, swirling and blocking the outflow. I would also extend the sides and bottom aft to prevent reverse swirling. But you said that doesn't work.

Try making a reverse outlet scoop replacing that shiny piece with it's louvers. They may actually be doing nothing. If the reverse scoop projects outward 1-1/2" +/- or so it will be touching the higher velocity air being spilled out sideways from the nose cowl. Those louvers may just be within a dead air area.

I had a set of louvers similar to those on a 185 which were not installed smoothly. When they were fitted better they made a big improvement in cooling. Try a big reverse scoop using the existing fastener locations.

stewartb said:

0-375? Oil temps are okay? I think there’s a reason the SQ variants use angle valve 390s now.

After blowing my ring gear apart at the 2nd or 3rd start-up I keep my Pmags timed at about 4° after TDC. After the kick-back we had them at 6° after and it stayed that way until the 400 was recalled. Maybe retarding the timing is worth a try. I can switch timing curves at the panel and for my needs I can’t tell any difference so I use A.

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Hi Stewart, Engine is an Aero Sport 0320B2B, oil temp runs around 200 or slightly above on hot summer days, but for the most part oil temperatures are within normal range below 80 degrees fahrenheit outside temperatures.
Rick

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10.1 pistons on the 320?

skywagon8a said:

Interesting, from here it looks as though the air will spill back into the lower cowl, swirling and blocking the outflow. I would also extend the sides and bottom aft to prevent reverse swirling. But you said that doesn't work.

Try making a reverse outlet scoop replacing that shiny piece with it's louvers. They may actually be doing nothing. If the reverse scoop projects outward 1-1/2" +/- or so it will be touching the higher velocity air being spilled out sideways from the nose cowl. Those louvers may just be within a dead air area.

I had a set of louvers similar to those on a 185 which were not installed smoothly. When they were fitted better they made a big improvement in cooling. Try a big reverse scoop using the existing fastener locations.

Click to expand...

I also tried the reverse scoop with a slight lip with no results.

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Negative, 8.1 and running 100LL, kept compression low for auto fuel option if needed

KevinJ said:

10.1 pistons on the 320?

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FWIW, here are a couple of pics of my nephew’s old SQ. I believe his cowl was by Wayne Mackey and I see some differences that may help, especially if you followed dkandle’s actions and comments earlier in the thread. Good luck!

Rick, took me a min to put two and two together. I’ve watched you fly your cub a couple times. From what I remember, you fly a slatted cub as good as anybody I’ve seen…..I’m sure it’s a bandaid but I’d think your fuel flow should be closer to 15-16gph with a coarse prop? Won’t lower your temps 30 degrees however. Good luck as it’s damn frustrating throwing sh!t at the wall

rotto789 said:

I also tried the reverse scoop with a slight lip with no results. View attachment 58975

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I'm running out of ideas. That big lower exit opening just doesn't look right. If the exit is correct, then you are not getting enough volume in the intake. Or enough space once inside to smoothly change direction and to then flow down through the cylinder fins.

You don't have any large holes where the air can bypass the cylinders do you?

skywagon8a said:

I'm running out of ideas. That big lower exit opening just doesn't look right. If the exit is correct, then you are not getting enough volume in the intake. Or enough space once inside to smoothly change direction and to then flow down through the cylinder fins.

You don't have any large holes where the air can bypass the cylinders do you?

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Oil cooler is mounted on rear of plenum and I do have a couple 1 inch blast tubes for the pmags connected to the rear of plenum as well, however, I've tested with both blocked off and the result was again, no change. Still think I might completely redo the baffling and try to open up more room around the cylinders to allow more volume of air through. I'm also considering opening the side cowl doors to mimic the stock super cub air exits. These will be my last efforts to reduce temperatures. If this does not work, I'm returning to stock cub cowl.

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What’s inside that bottom fairing? Is anything faired inside or is it open? I don’t think a Cub’s cowl cheeks are magic but they are in airflow that effectively draws warm air out. Given how you’ve baffled behind the prop I’d say your inlet air looks like a typical Cub but the outlet air is very different. That’s where I’d focus my efforts. If your side scoops are still there I bet you could close off that bottom outlet and see improvement. It’s easy to visualize that rear area in the lee of that large ramp profile being in an eddy. It may not be but with those scoops there it would be easy to test.

The Mackey version of the lower cowl isn’t coved. It’s square on the back. More interesting is how streamlined it is at the front.