Ly-Con 160HP O-320-E2D And Similar - CHT issues

[Jon Wilder]

I've flown a few different 172's with the 160hp Lycoming O-320-E2D mods that replace the 7:1 pistons with 8.5:1 pistons. In every single one, all it seems to do is increase the climb CHTs. Now you're stuck either having to dial the power back (giving you the same climb rate) OR doing a step climb.

The whole point of horsepower upgrades (or so I thought) was better climb performance. But if you're having to step climb or climb at a lower power setting, what did you really gain for that 10hp?

 

[Dan Thomas]

Do you have a single-point CHT, or an engine monitor that has CHT probes in every cylinder? The old single-point probes are subject to overreading when the engine grounding to the airframe is less than perfect.

An extra 10 HP is less than a 7% increase. It shouldn't drive the CHTs up much at all. In pretty much all the cases of high CHTs I've come across, I find the cooling baffles and seals in poor condition, leaking much of the cooling air and reducing the pressure differential between the top and bottom of the engine. Sometimes I have found intercylinder baffles missing altogether. They're a pain to install, tempting some folks to just toss them. Another common defect is a missing induction filter baffle; it seals off the gap around the filter, preserving the low pressure under the engine created by the cooling air outlet. If the prop blast can get in there you will have hot cylinders.

Leaking induction systems can let air in and lean the mixture and drive CHTs up. All those intake hoses and their clamps need periodic inspection. The gaskets between the intake elbows and the head sometimes get blown out and let air in. They get blown out when a pilot accidentally switches the mags to OFF during the runup, then back to ON, getting that big bang in the exhaust, sending a concussion back through exhaust and intake valves during their overlap, and blow those intake gaskets. If you switch to OFF, let the engine die and restart with the throttle closed. Saves the exhaust system and some other stuff.

 

[kyleb]

In addition to what Dan said, timing can be an issue too. A few degrees of increased (unplanned) advance can cause a noticable CHT rise.

 

[Stewartb]

Higher compression requires higher fuel flow. That’ll solve the climb temps problem, then you lean it for level cruise and enjoy better miles per gallon than with the lower compression engine. The higher you go, the better increased compression will serve you.

What are you seeing for CHTs? As long as they’re 425° or below in climb and run at <400° in cruise? I wouldn’t worry.

 

[idahoflier]

My view is that the climb performance gain should be viewed in terms of the first 1,000 - 1,500 feet vs up to cruising altitude. Climb to a safe altitude and then worry about cooling and how to manage the climb to cruising altitude. In mountainous terrain with high DA's an extra 10HP is always welcome. If I had an O-320 powered C172 and could upgrade it from 150 HP to 160 HP at overhaul I would do it.

 

[Jon Wilder]

Higher compression requires higher fuel flow. That’ll solve the climb temps problem, then you lean it for level cruise and enjoy better miles per gallon than with the lower compression engine. The higher you go, the better increased compression will serve you.

What are you seeing for CHTs? As long as they’re 425° or below in climb and run at <400° in cruise? I wouldn’t worry.

If I climb at anything above 2400 RPM it'll get up into the high 400s if I'm not watching.

About the best climb configuration I can use on it is 85 KIAS @ 2400 RPM. The back cylinders stay around 400-415°F at that climb power.

Granted, 2700 RPM is the 5 minute METO power rating on this engine, and 2500 RPM (150hp) continuous, according to the STC.

 

[Jon Wilder]

My view is that the climb performance gain should be viewed in terms of the first 1,000 - 1,500 feet vs up to cruising altitude. Climb to a safe altitude and then worry about cooling and how to manage the climb to cruising altitude. In mountainous terrain with high DA's an extra 10HP is always welcome. If I had an O-320 powered C172 and could upgrade it from 150 HP to 160 HP at overhaul I would do it.

At that point why not upgrade to something like the Penn Yan Superhawk 180hp O-360-A4N?

 

[Stewartb]

If I climb at anything above 2400 RPM it'll get up into the high 400s if I'm not watching.

About the best climb configuration I can use on it is 85 KIAS @ 2400 RPM. The back cylinders stay around 400-415°F at that climb power.

Granted, 2700 RPM is the 5 minute METO power rating on this engine, and 2500 RPM (150hp) continuous, according to the STC.

What’s your fuel flow? How much leaning authority do you have?

 

[Jon Wilder]

What’s your fuel flow? How much leaning authority do you have?

I'll have to go back and download the EIS data.

I have a bit of leaning authority. In accordance with Lycoming Service Instruction 1094 Rev D, I usually leave it full rich in the climb unless/until it becomes necessary to lean for restoring smooth engine operation.

Leaning Lycoming Engines

Revision “D” to Service Instruction No. 1094 supersedes all previous recommendations and should be used for engine leaning during normal flight operations. All leaning recommendations are based on calibrated instrumentation. Lycoming strongly recommends that all engine instrumentation be...

www.lycoming.com

 

[Stewartb]

What carb mods were included in the STC?

I’ve had plenty of experience chasing high CHTs after power increases. Fuel has been the solution. Reaming the main jet a little bit can yield very surprising results, and overall fuel consumption doesn’t change much. If you can’t lean >200° from full rich to peak while in level cruise, I’d say you need more fuel flow. If you have that, I’d be looking at baffles, particularly for a spacer behind #3. Blocking part of #1 and 2 may reduce temps at 3 and 4. Some guys fabricate ramps. My engines have flat baffles and they do the job. The pic is #1 on my IO-390.

 

[AV8R_87]

If I climb at anything above 2400 RPM it'll get up into the high 400s if I'm not watching.

What's the OAT?
Even on hot days, climbing at full power, well over 2400rpm, i rarely get above 375 on the rear cylinders. They'll get hotter if I have to lean for best performance on high DA days. Definitely something off on your side, either baffling or fuel flow. I see about 15gph on take-off. Do you have a fuel flow indicator?

 

[Jon Wilder]

What's the OAT?
Even on hot days, climbing at full power, well over 2400rpm, i rarely get above 375 on the rear cylinders. They'll get hotter if I have to lean for best performance on high DA days. Definitely something off on your side, either baffling or fuel flow. I see about 15gph on take-off. Do you have a fuel flow indicator?

I have a full on EIS. I usually see around 12-13 gal/hr on climb. I'll have to download the EIS data to be 100% certain.

 

[Dan Thomas]

Regarding fuel flow: Has the mixture control rigging been checked? If it's off, the mix lever on the carb may not be reaching full rich.

I have inspected airplanes in which EVERY control, both engine and flight, was out of rig, sometimes badly. It seems that there is incompetence in every field. Aviation is no exception.

 

[Jon Wilder]

What's the OAT?
Even on hot days, climbing at full power, well over 2400rpm, i rarely get above 375 on the rear cylinders. They'll get hotter if I have to lean for best performance on high DA days. Definitely something off on your side, either baffling or fuel flow. I see about 15gph on take-off. Do you have a fuel flow indicator?

I went and flew the pattern today. Right at 15 gph on takeoff.

 

[idahoflier]

At that point why not upgrade to something like the Penn Yan Superhawk 180hp O-360-A4N?

Because it would be a significant difference in price. Don't get me wrong, the O-360 upgrade increases the utility of a C172, but unless you're really attached to an aircraft it doesn't make much financial sense when you can sell the C172 and buy a C182...