Engine Cooling Revelation

[Nev]

I read this thread a while back and was impressed with Bobby's work, and only today got around to checking the pressure differential on my cowling. I didn't have any cooling issues as such, those were ironed out during the phase one.

The main take away for my results are that my pressure differential is less than Bobby's, and probably suits our more temperate climate whereas Bobby was dealing with very warm ambient temps. But I have two cabin heaters and barely use one in the middle of winter, so I wondered what would happen if I removed one. Would it increase the pressure differential enough that the CHT's would run lower, and I could then run closer to peak EGT (from LOP), thereby allowing an increase in speed? It appears that it might work. It'll also save a couple of pounds in weight.

Removing one heater increased the differential by 0.5", and already I could notice a small reduction in CHT. Closing the oil cooler butterfly valve also increased the pressure differential by another 0.5". I also checked that my cowl vents are contributing to an increase in pressure differential as they should. They are. The vents all lie in the low pressure side, and are lowering that pressure further by approximately 0.5" each. When I taped over them, all the temps got hotter. But the oil cooler and cabin heaters come from the high pressure side, and those had the greatest effect.

I might look at reducing the oil cooler inlet for both settings, or even repurposing the now unused spare heater control to the oil cooler valve, because it has a pronounced effect not just on the oil temperature but also a 20% effect on cowling pressure differential.

My Manometer didn't have a restriction in it, so some data smoothing was required. I tested two power settings, 22"/2200rpm/38lph and 26"/2200rpm/42lph.

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[Nev]

Thread drift.......

Just to add to this in regard to the heater muff. I rang Clint at Vetterman exhaust this morning. My question was if I remove the shroud from the heat muff, can I then run it or do I need to modify the underlying exhaust. Clint advised that it can now run it as it is with the shroud removed. He did mention that the stainless shroud does have to be removed otherwise with the airflow disconnected the heat muff can overheat. The photo below shows what is underneath the shroud.

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[AKKen07]

My CHTs were pretty high so far (420+ in high Pwr cruise on #6, #1 got to the same in a climb). Slow flight was short lived due to engine overtemping, etc. on and this was all at below freezing temperatures outside. Even one flight at zero F. My last flight showed a decrease of 40 degrees after several mods. I added a 2” lip, sealed the cowl hinge lines with baffling, added a round fairing at the firewall to tunnel transition, and replaced my oil inspection door with one that seals better. I also secured the baffling rubber in a couple places where I wasn’t sure it was sealing. I can now do the test flights that require sustained high power. Victory!

[Light&Sweet]

This has been a great thread posting.

Mother nature figured it out. While not for cooling, certainly efficient flow. This Great White has been around and seen some things.
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[Bcone1381]

FYI, I like data. Easy air pressure data collection is achievable using a manometer. I will be doing this when my Patrol is done.

https://www.amazon.com/Ehdis-Digital-Manometer-Pressure-Accuracy/dp/B07L641Q7L/ref=sr_1_1_sspa?keywords=manometer&qid=1680090597&sr=8-1-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExVEtWOERHOTZFWlYyJmVuY3J5cHRlZElkPUEwNzk2MjI5VEU1N0JKTVZWVUU1JmVuY3J5cHRlZEFkSWQ9QTA5Mzk5ODVBVko3RTg3SkhNMlImd2lkZ2V0TmFtZT1zcF9hdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl