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Tip: Cylinder Air Dams

N941WR

N941WR

Legacy Member
The new baffle kits (You know you have the old baffle kit, if the drawings are hand drawn.) include air dams that get riveted in so as to deflect the air up and over the heads of #1 and #2 cylinders.

The only problem is that they are riveted in place and if you need to adjust them, and you will need to adjust them, you have a problem.

My suggestion is to replace the rivets on the ramps leading to the cylinder heads with flush rivets and platenuts. Then you can make a simple air dam that uses those three platenuts and when you need to adjust the air dams, you can remove them, trim them to size (or replace them, when you trim too much off), and screw them back in place. Remember, that the left and right air dams will be different because the platenuts will be in different places, if you put them where the rivets are supposed to go.

2012-07-04_15-38-52_41.jpg


The other option is to forgo the air dams altogether and use foil tape, available at your local hardware store.
 
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humptybump said:
Perhaps a niave question but I'm going to ask it anyway ...

"what is the purpose of the air dam ?"
Click to expand...

To reduce the cooling air to the front cylinder(s) and deflect that air to the rear cylinder(s). Say your in-flight CHT's are 340F on #1, 350F on #2, and 380F on #3 and #4. The goal would be to install air dams of sufficent height on #1 and #2 to balance all 4 cylinders at (say) 360F.
 
Kyle Boatright said:
To reduce the cooling air to the front cylinder(s) and deflect that air to the rear cylinder(s). Say your in-flight CHT's are 340F on #1, 350F on #2, and 380F on #3 and #4. The goal would be to install air dams of sufficent height on #1 and #2 to balance all 4 cylinders at (say) 360F.
Click to expand...



Or in the winter to block more air to get the CHTs up by putting in taller blockers.
 
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Thanks Kyle.

I wanted to ask the question because I have done several searches lately for "low CHT" and found nothing. My CHTs have almost a 100F separation with the low one being around 260F in cruise and the high one at 355F.

I will be checking plugs, etc. this week but if I find nothing, I will plan to play a bit with air dams.
 
humptybump said:
Thanks Kyle.

I wanted to ask the question because I have done several searches lately for "low CHT" and found nothing. My CHTs have almost a 100F separation with the low one being around 260F in cruise and the high one at 355F.

I will be checking plugs, etc. this week but if I find nothing, I will plan to play a bit with air dams.
Click to expand...

You might swap around your CHT probes too. Occasionally you get a bad one. If Cylinder #3 (or whatever) is the high (or low) one and you move that probe to another cylinder and that one becomes the outlier, the probe may be the problem...
 
I had Superior investment cast cylinders and #2 was the coldest even with the temperature risers. Replaced cylinders with ECI cylinders after 2,200 hours and now #2 is a lot hotter. Removing the temperature riser and it is very close to the other three. #1 still has the temperature riser installed. This is with an O-320 CS.

Note: The ECI cylinders are the through hardened steel barrel just like the Superior was. The Superior through hardened steel cylinders still showed the cross-hatch hone patter and measured out new spec including the choke.
 
N941WR said:
My suggestion is to replace the rivets on the ramps leading to the cylinder heads with flush rivets and platenuts.
Click to expand...

Yep, good idea Bill. I did that with mine too. It is especially easy for the horizontal cold air induction engines (the ones that use the snorkel to take air from the No.2 cylinder front baffle ramp) as there is already a need for screws in that area to hold the air filter in place. Though I kept the original rivets and positioned the three screw holes between the rivets. I needed to matchdrill the rivet holes to the flange on the bottom of my air dam then oversize them enough to provide clearance for the rivets. Did likewise on the other side.

Steve
 
I just cut my down last week. Took about 1/2" off and it's pretty much evened out the temps.

I was going to pull the baffle off and go this route but Stein Bruch gave me a piece of stainless and said "put this behind it and cut it with a Dremel; it'll be faster."

2012-07-01_16-31-52_27.jpg


I could probably cut more down more, but I want to see what winter brings -- assuming that winter ever comes to Minnesota again (it didn't last year).
 
humptybump said:
Thanks Kyle.

I wanted to ask the question because I have done several searches lately for "low CHT" and found nothing. My CHTs have almost a 100F separation with the low one being around 260F in cruise and the high one at 355F.

I will be checking plugs, etc. this week but if I find nothing, I will plan to play a bit with air dams.
Click to expand...

Fuel injected?
 
Bob C.

How many degrees in temp did the 1/2" reduction yield? I need to reduce my #1 cylinder temp a little.
 
aluminum tape works great for establishing the size needed. Found in the ductwork section of the local HD.
My "temporary" foil tape air dam is going on three years now, been replaced a few times.
 
I have the old school baffels.
Without any air dam, the number 1 cylinder was 70-deg cooler than the others. With this air dam it went 50-deg hotter than the others. 120-deg difference.
1342060575481.jpg


Trimming little by little until I had cut about 1/2" off yielded an 11-deg difference from coldest to hottest.
1342060613059.jpg


This is a o-320 carb.
 
Guys,

I don't understand the focus on the air dams. It strikes me as giving attention to the wrong place. Numerous NACA studies have supported minimizing the drag "into and through" the baffles and regulating the amount of throughput by adjusting the exit.

Simply put, this approach provides the lowest cooling drag, something Mr. Axleson is very sensitive to.

What is different about the RV baffles that supports a different approach?

Onward and upward

Marc Bourget
 
Marc Bourget said:
Guys,

I don't understand the focus on the air dams. It strikes me as giving attention to the wrong place. Numerous NACA studies have supported minimizing the drag "into and through" the baffles and regulating the amount of throughput by adjusting the exit.

Simply put, this approach provides the lowest cooling drag, something Mr. Axleson is very sensitive to.

What is different about the RV baffles that supports a different approach?

Onward and upward

Marc Bourget
Click to expand...
Marc - the way the inlet is designed, cylinder #1 and #2 are directly in front of the air stream. The Air Dam simply blocks that ram air and redirects it into the plenum. It keeps it from super cooling those two cylinders. Adjusting the exit area would require the cylinder wrap on the front of #1 and #2, or the inter cylinder baffle to be modified somehow to partially block between the cylinder fins.
That would be a lot of fiddling around for very little if any gain in my opinion.
The Air Dam is perhaps not ideal, but very simple and effective.
 
Marc Bourget said:
Guys,

I don't understand the focus on the air dams. It strikes me as giving attention to the wrong place. Numerous NACA studies have supported minimizing the drag "into and through" the baffles and regulating the amount of throughput by adjusting the exit.

Simply put, this approach provides the lowest cooling drag, something Mr. Axleson is very sensitive to.

What is different about the RV baffles that supports a different approach?

Onward and upward

Marc Bourget
Click to expand...

Because the subject and primary goal of this topic regarding most builders/flyers here is balancing of CHT's, not reduction of drag. You may be right for reducing drag (however that's not what this thread is about), but it does little for balancing cylinders in a stock configuration on an RV. Dams (and tape like me and many others have) works great for this purpose and have been used thousands of times....

Cheers,
Stein
 
Where is tape applied

SteinAir said:
(and tape like me and many others have) works great for this purpose and have been used thousands of times....

Cheers,
Stein
Click to expand...


When using tape (assuming foil?) for this purpose of directing air flow, where/how is the tape applied? Is it applied directly to the cylinder cooling fins?
 
Dbro172 said:
When using tape (assuming foil?) for this purpose of directing air flow, where/how is the tape applied? Is it applied directly to the cylinder cooling fins?
Click to expand...

I cut a strip long enough to cover both the cylinder head and barrel. It stood up about an inch to an inch and a half. Easy to adjust and replace.

I attached the tape to the ramp and then to the cylinder so the air would be forced up over the cylinder and not down.
 
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