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  #21  
Old 10-26-2012, 10:53 PM
Lars Lars is offline
 
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Location: Davis, CA
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I'll add fly it and see how it works. Having seen this thread before I did my baffles, I made a form and created a nice big clearance behind #3. Turns out it's my coolest-running cylinder. NUmber 2 on the other hand, which has the same fin issue except facing forward, tends to get hot on climbout but then drops to mid-range in cruise. On that cylinder I simply bent/tweaked the baffle a bit, rather than doing a nice job forming a bubble in the baffle. Mostly because I originally ran the Van's air dams on the front two cylinders; turned out they didn't like them and I removed them.

A neighbor has a (not a Van's) with a parallel valve Lycoming O-360 that was factory-new in the late 70's. Still has the original cylinders. They look more like the ECI cylinders than the others we see with no fins in the vicinity of the exhaust valve.
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  #22  
Old 10-27-2012, 08:10 AM
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Captain_John Captain_John is offline
 
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Lars,

Wilco!

That is why this is an experiment! I will give it a go.

I hope it runs as cool as yours!

Thanks both!

CJ
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  #23  
Old 06-28-2013, 08:24 AM
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Quote:
Originally Posted by Lars View Post
NUmber 2 on the other hand, which has the same fin issue except facing forward, tends to get hot on climbout but then drops to mid-range in cruise. On that cylinder I simply bent/tweaked the baffle a bit, rather than doing a nice job forming a bubble in the baffle.
Hey Lars, any chance you could post a photo of how you "bent/tweaked the baffle a bit" on that #2 cylinder? I'd love to find an easy fix to getting the temps on this one down. Thanks.
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  #24  
Old 07-08-2013, 08:27 AM
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DanH DanH is offline
 
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Yep, size matters. In retrospect I should have installed the larger bypass duct on #3 (right rear) and the small hammerformed duct on #2 (left front).

Had the airplane down for a new cooler, so I adopted the idea of a large built-up bypass duct on #3, as presented by Mike Robinson. Didn't go quite as large. This one provides about 1/4" of space to pass air around the pinched no-fin area on the back of #3:



The result appears to be a reduction of about 10F. It brings #3 into reasonable accord with 1 and 4. Still have a 24F spread with #2, but I think correcting that (if it really matters) will require reducing flow past that cylinder.

Here's a shot taken yesterday, preliminary testing, in a cruise condition which many would call abusive...roughly 30-50 degrees rich of peak. The cowl exit door is closed so outlet area is around 30 sq in, with an OAT over 60F:



Now here's what I found really interesting. OSH is in three weeks, meaning we all get to drag it in from Ripon at 90 knots. With a new oil cooler and a baffle tweak I just had to check slow flight cooling performance with the cowl exit door open. It was about 80F OAT down low, maybe a little more. I think this will work just fine:



Total CHT spread is now 9 degrees, and #3 is no longer the warmest cylinder.
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Last edited by DanH : 09-03-2018 at 08:03 AM.
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  #25  
Old 07-08-2013, 10:47 AM
alpinelakespilot2000 alpinelakespilot2000 is online now
 
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Quote:
Originally Posted by DanH View Post
Had the airplane down for a new cooler, so I adopted the idea of a large built-up bypass duct on #3, as presented by Mike Robinson. Didn't go quite as large. This one provides about 1/4" of space to pass air around the pinched no-fin area on the back of #3:
Thanks for the experiment Dan. To see if I understand you correctly...

For those of use who have used a washer under the baffle connected to #3 to try and get air there, what we really need is not the 1/16" that the washer provides, but something more along the lines of 1/4"? Obviously 4 washers are probably not going to work here, but was your modification essentially trying to accomplish the same thing?

Also, hard to tell from the picture, but what did you use to seal the sides of the extra piece you riveted to the back of the baffle. It doesn't look like aluminum.

Thanks for the help, as I'm trying to do everything possible to get my #3 down at least 20F.
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Last edited by alpinelakespilot2000 : 07-08-2013 at 10:51 AM.
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  #26  
Old 07-08-2013, 11:33 AM
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az_gila az_gila is offline
 
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Just another data point from a 1999 Lycoming factory cylinder -



Not only is there a "no slot area" as has been mentioned previously, but the adjacent fins are somewhat blocked by flashing from poor molds.

If a cylinder has a poor casting blocking airflow then the "add a washer" technique might be quite beneficial rather than the targeted "slot" technique.
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  #27  
Old 07-08-2013, 11:51 AM
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DanH DanH is offline
 
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Steve,

The new duct you see riveted into place has bent aluminum ends. They just have a lot of Permatex Ultra Black (same as Loctite 598) silicone smeared on them to seal the edge.

Back in post #10 of this thread I professed to not know the exact size needed for these ducts. I still don't, not really. The 1/4" I used here seems to be pretty close. However, there are variables like the fin differences on angle and parallel heads, differences in baffle fit and sealing, differences in inlet shape, well, you get the idea. Heck, look at the CHT values with my cowl exit door open and closed at different speeds and altitudes...with the same baffle!

The "problem" with placing a washer under the baffle at the AN3 bolt is that it spaces the tin away from the cylinder where there are no fins. That seems kinda useless, but you could squirt some silicone in there (black rectangle, post #1) to block the wasted flow....and clearly it has worked fine for lots of builders to date.
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  #28  
Old 07-08-2013, 12:17 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by az_gila View Post
Not only is there a "no slot area" as has been mentioned previously, but the adjacent fins are somewhat blocked by flashing from poor molds.
If a cylinder has a poor casting blocking airflow then the "add a washer" technique might be quite beneficial rather than the targeted "slot" technique.
Either approach will bypass the flashing and shallow fin depth.
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Last edited by DanH : 09-03-2018 at 08:06 AM.
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  #29  
Old 07-08-2013, 06:39 PM
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Toobuilder Toobuilder is offline
 
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Dan, I take it you are not addressing the upper fins with your latest mod?

If not, it might be worth while to add something to draw the air through the upper fins on the way to your duct just to see if it is of any measurable benefit.
I recently duplicated "my" baffle mod on a buddy's 200 HP RV-7 to good effect. Would be nice to know if the upper portion of my duct is doing anything
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  #30  
Old 07-08-2013, 07:09 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Dan, I take it you are not addressing the upper fins with your latest mod?
Well, actually yes. I started a baffle plate up there but it's not complete yet. You and I are curious about the same thing.
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