Increasing #1 CHT, Decreasing #3 CHT

[tx_jayhawk]

I have an O-360 on my 7A with a Sam James cowl and plenum. I have found that my #1 cylinder runs 40 - 60 degrees cooler than #3, and #2 / #4 are within 10-15 of #3.

Question is this...if I want to lower #3 and raise #1, what is the best way? I do not have the standard baffles so the setup is a littel different. Should I glass up an extension to the plenum ramp to "force" more air to the #3 instead of #1? Or, rivet a ramp to the small piece of metal between #1 cylinder and the plenum ramp? I think my plenum / baffles are otherwise sealed quite good.

Similar question...what kind of CHT / oil temp rise do people see when they lean out the engine? It seems I get a fairly notable rise when leaned to 100 rich of peak?

Thanks,
Scott
7A

[Kyle Boatright]

Use aluminum tape to cover the lower portion of the exposed face of #1. Experiment until you get the height dialed in to best balance temperatures. Then fabricate one out of aluminum and pop rivet it in place.

[Greg Arehart]

Scott,

Not sure why you would get a temperature rise at rich of peak. Peak by definition is the highest EGT and *should* represent the ideal fuel:air. Rich should be cooler as there is excess fuel that helps cool the cylinder. Ideally, at any mixture rich of peak, you should be actually burning the same amount of fuel as at peak (since it is now oxygen-limited), but the cooling effect of unburned fuel lowers the temperatures. Lean should also be cooler than peak as there is less fuel being burned, thus less heat energy being produced.

greg

[tx_jayhawk]

Thanks Kyle. I will give that a try.

Greg,

When I say I get a temp rise, I am comparing the temperature with the mixture knob all the way in (XXX rick of peak) vs leaning to "only" 100 rich of peak.

Although I am still experimenting, it seems increasing CHT (and to a lesser extent oil temp) are limiting how lean I run it.

Thanks,
Scott

[Greg Arehart]

Scott,

At full rich, my EGTs are about 1200 degrees. At peak, I get around 1500 degrees (at near sea level - never that high at Reno which is 5000 ft). The absolute numbers are fairly meaningless (unless they are way low or something) because it will depend on probe location down the exhaust. For reference, mine are 6 inches from the cylinder.

My CHTs (at Reno) can easily exceed 400 on a warm day on takeoff, if I take off with the engine leaned out too much. I will lean on the ground for runup (at 1900 rpm) to optimal RPM and then push in the mixture about halfway from there before takeoff. If I do this, my takeoff CHTs stay below ~390. I also level off as soon as I'm off the ground and pick up speed for cooling before beginning my climbout.

In the air, once everything is stabilized (~8500 ft) I never see CHTs above about 380 and typically they are in the 350 range when running ~2500 rpm (will depend somewhat on OAT).Once stabilized, the difference between rich (never full rich), peak, and LOP on the cylinder heads might be 20 degrees at most.

Hope this gives you some useful reference data.

greg