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Cylinders #1 and #2 Hot

I have a cylinder head temperature situation on my RV-7A that I don’t understand, and I’m hoping someone can enlighten me. Cylinders #1 and #2 are running about 30 deg F hotter than #3 and #4. I have searched through VAF and have not seen this issue discussed. We are still in phase one test, with about 15 hours on the engine. The engine is an Aerosport O-360-A1A with ECI Titan cylinders turning a Hartzell BA prop. Mag on the left, Lightspeed Plasma II on the right. We have sealed every air leak we can find. We tried cutting down the dams on the front cylinder heads, which made the rear cylinders run cooler, but didn’t do a thing for #1 and #2. We installed Van’s lower cowl louver kit which lowered all CHTs significantly, but we’re still seeing about 400 degrees on the front cylinders and about 370 degrees on the rears in steady-state cruise at 75% power. We have not put the wheel pants on yet, so cruise speed is about 125kts.
From what I have read, these temperatures are acceptable for a new engine, but I sure don’t understand why there is such a discrepancy between the front and rear pairs of cylinders, with #1 and #2 running hotter. It doesn’t seem intuitive. Is it a problem?
Thanks in advance.
 
Hi Paul your temperatures are not out of line from the norm for a engine not fully broken in. It’s also really normal to have to really trim down those front cylinder air dams to get the cylinders to cool more uniformly. On my recently sold rv6a that I built I had to remove the front air dams all together in order to get those temps uniform. Also the wheel pants and fairings will improve the cooling greatly as well.

Thanks
Bill
 
I would focus on the cruise speed. 125 Kts is the speed most people climb at. I suspect when you get the wheelpants on there will be large improvements. 125 seems slow even without pants so I would also check your ASI.
G
 
slow

I would focus on the cruise speed. 125 Kts is the speed most people climb at. I suspect when you get the wheelpants on there will be large improvements. 125 seems slow even without pants so I would also check your ASI.
G
Good suggestion - I'm closer to 160 at that power setting. No wheel pants during this flight. (I believe my IAS is off by about 5 or so kts.)

HB-YMM IAS-FF-DA-RPM 20200904.png
 
This is what I did, along with raising the baffles ahead of cyl 1&2 which were originally below the centreline of the cylinder barrels.

https://vansairforce.com/community/showpost.php?p=1455893&postcount=4

I suspect that plugging all the gaps that allow cooling air to escape anywhere other than through the cooling fins, especially those created by the lower inter-cylinder baffles, leads to higher back pressure above the cylinders (in the quasi "plenum") and therefore more even airflow ejection and heat dissipation. I guess this is the result of the inlet flow rate being greater than the cooling fin ejection rate.

This was evident when I saw no meaningful change between all CHTs with the hot air vent above cyl 3 either plugged or unplugged.

Unfortunately it's not something I can quantify with engineering analysis. It just makes intuitive sense to me and has proved very effective here in the Australian heat. I hope some of this information helps you.
 
My guess is that the 30 degrees is not due to cooling, but rather your fuel/air distribution spread. Do you have an engine analizer with EGT and CHT on all 4 cylinders? Do you have Fuel Flow? If so, set up in cruse and then lean to see when each cylinder hits peak EGT and the corasponding Fuel Flow.

Reguardless of the above, I think your temps, while "normal", are higher than I like. You are going to struggle to climb on a hot day. My first step would be to enlarge the cowl exit area, either with lovers or by cutting back the trailing edge. Some have had success with putting an air foil on the engine frame bottom tube to reduce turbulance generated at the exit.

What oil are you using, and what are your oil temps?
 
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I had higher temps than I liked until installing the gear fairings and wheel pants. Do that next, since you already installed louvers. It's good to leave the gear fairings/pants off until the engine is broken in, which should be done by now, unless you have chromed cylinders.
 
I had a similar experience with my new engine on my 7 - initially, they were all a bit hot, but #1 really stood out by 20-25 deg

Hobbs: 4
75% power
CHT 385-410 (#1 hottest by 20 F)
OAT 20C
FF 13.6 GPH
Alt: 5500
Oil temp: 185 F

I removed the dam from number 1; that dropped the temps immediately by 20 F to get it in range with the rest (385 F ish).

After doing a aggressive leak quest (found a few significant ones on the rear baffle) and putting on the wheel pants, I'm now seeing this for cruise:

Hobbs: 27
75% power
CHT 350-359 (#1 in the middle)
OAT 26C
FF 13.8 GPH
Alt: 5500
Oil temp: 183 F

All the cylinder temps were slowly trending down as break-in continued, however, removing the dam, plugging leaks, and adding the pants (+9 kts IAS) helped a lot. All the cylinders are within 10 F of each other in cruise.
 
Hi CHTs and Lessons Learned

My second RV-7 was supposed to be "exactly the same" as my previous RV-7 -- Same Engine, Same this, Same that... except it wasn't.

A good friend of mine reminded me to fly the airplane that I have and not get too bogged down in comparisons between supposedly identical aircraft.

In the new RV-7, I noticed that my CHT's were hot relative to the old airplane (400°F+ vs 330°F at same DA and settings) and I spent a lot of time hitting my head against hard objects before I realized what the problem was -- and the differences were..

The deltas and the lessons learned:

1. Gear leg fairings and wheel pants -- old airplane had them at first flight, new airplane didn't; worth 10 - 12Ktas and about 30°F of CHT and 15°F of Oil Temp.

2. Ignition Timing -- old airplane was 20° BTDC/base timing, new airplane was 22°; worth about 10°F of CHT - dropped immediately when I reverted to 20° BTDC.

3. Baffles -- make sure the inter-cylinder baffle kit is installed, the small tab at the barrel of the #3 cylinder is bent @ 90° and sealed to the case/barrel, the baffle wraps are indeed wrapping around the bottom of the cylinder heads and not deformed by the fin shape transition, a check for leaks, install the AN960 washers at the front of #2 and back of #4...
 
I have a cylinder head temperature situation on my RV-7A that I don’t understand, and I’m hoping someone can enlighten me. Cylinders #1 and #2 are running about 30 deg F hotter than #3 and #4. I have searched through VAF and have not seen this issue discussed. We are still in phase one test, with about 15 hours on the engine. The engine is an Aerosport O-360-A1A with ECI Titan cylinders turning a Hartzell BA prop. Mag on the left, Lightspeed Plasma II on the right. We have sealed every air leak we can find. We tried cutting down the dams on the front cylinder heads, which made the rear cylinders run cooler, but didn’t do a thing for #1 and #2. We installed Van’s lower cowl louver kit which lowered all CHTs significantly, but we’re still seeing about 400 degrees on the front cylinders and about 370 degrees on the rears in steady-state cruise at 75% power. We have not put the wheel pants on yet, so cruise speed is about 125kts.
From what I have read, these temperatures are acceptable for a new engine, but I sure don’t understand why there is such a discrepancy between the front and rear pairs of cylinders, with #1 and #2 running hotter. It doesn’t seem intuitive. Is it a problem?
Thanks in advance.

Does it change based on throttle position? Carbed 0-320s have notoriously poor fuel distribution from my experience. WOT #1 and #2 heat up for me. When I pull back power slightly, #3 and #4 heat up and #1 and #2 cool down.

If this is the case for you, air dams and/or baffling will not solve the problem (at least entirely.) You may just have to live with it. That said, it's also a way to manage temperatures. When 1 and 2 heat up in climb I pull power back a bit until 3 and 4 become the hottest, then I may go back to full power to cool 3 and 4 down. Usually I can do that back and forth until I get high enough that I'm not producing enough power for CHT's to get past 380F anyway. Others have also found that using a bit of carb heat can help even out the temperatures. I've found that to work a little bit in certain situations. This all may be a bit clumsy compared to an I0-320, but it works fairly well once you get to know your engine.
 
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Having the same problem except with almost 800 hours on the engine. would recommend throttling back and keeping mixture a little rich. Also check baffling for leaks.
 
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