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Cooling Ducts and CHT's

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Cooling Ducts and CHT's

Postby diablo » Sun Feb 15, 2015 5:56 pm

Cooling Duct Deflectors

Something I have done which has made a huge difference to high cylinder head temps is the addition of the deflector in the cooling duct. This modification was recommended to me by the local agent who received the information from Australia. There are two things they advised, placing a deflector at 45 degrees to the horizontal above the two back cylinders and increasing the size of the inlets on the top cowl. I have only done the deflector so far and this has proved to be quite sufficient.

deflector.JPG
deflector.JPG (8.97 KiB) Viewed 2283 times


The climb temperature has dropped from 200 to 160 degrees, with just over 100 at cruise from the original 160. (I have the wide ducts) Everybody who has done the modification has had similar results. We are all very pleased.

At the time of writing - new jab cooling ducts are the narrow ones with the deflector already fitted.

narrow Ducts.JPG
narrow Ducts.JPG (14.1 KiB) Viewed 2283 times


Some advice from Jabiru about cooling ducts.

Jabiru Advice.JPG
Jabiru Advice.JPG (69.44 KiB) Viewed 2283 times


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Re: Cooling Ducts and CHT's - Jabiru Instructions

Postby diablo » Sun Feb 22, 2015 6:23 pm

Ram Air Ducts.pdf
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Re: Cooling Ducts and CHT's

Postby Brent » Tue Sep 01, 2015 3:30 am

I performed the Jabiru recommended modifications to my ducts as per the above post on my 6 cylinder engine but found that they didn't give me the lower temperatures that I was chasing.

After some mucking around I ended up adding some "ramps" in the front of the ducts - plenty of aircraft already use these including RV's and similar. This made a huge difference. Add that to opening up the rear of the ducts (pic is of my initial attempts to do this so is a little messy) and adding the tabs at the base of the cowl. The ducts that come with the Camit engine now include ramps.

These three changes brought down the highest temps from 210c to around 120-140c, a HUGE difference !

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Re: Cooling Ducts and CHT's

Postby weirdfish » Tue Sep 01, 2015 1:21 pm

I've been faffing about for ages trying the lower and even up CHTs by adjusting the top deflectors. I was really struggling with the rear most cylinders 5 & 6. I had added ramps and blocked gaps with small gains here and there. Eventually I removed the deflectors to see what happened. It reversed the temps with 5 & 6 being the coolest per side and 1 & 2 being the hottest.

With this in mind I theorised that with the air being deflected from the top of the duct, there was no clean air past the first deflector. I thought I'd try adding deflectors that only just cleared the top of the middle heads leaving the duct above it clear of obstruction and delivering relatively smooth air to the rear heads, which I reinstated the full deflector. This worked wonders for me with only needs to address number 2 with a small deflector mounted on the side of duct.

if only I could now get the port side to match the starboard side when on the ground, they are pretty well balanced in flight, I'd be a happy man. For what's it's worth I have a solid lifter with the narrow duct with the plug leads on the outside.
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