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Plenum

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DCS317(at)aol.com
Guest

Posted: Wed Jan 18, 2006 3:35 pm Post subject: Plenum

I'd like to change to a plenum and make it myself rather than use the  

available "off the shelf" types.  Aluminum vs. fiberglass?  Anyone  made one similar 

to Diamond Aircraft's two-part plenum? Reason for  change--running ok except 

hot weather CHTs go to 425+ on a couple cylinders  despite injector sizing 

changes on my IO-540 with Lasar and proper  baffling.  Please no comments on the 

IO-540--I just like excess  power!

 

Don Schmiesing

Seattle 

110 hours on 417DS

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Terry Watson

Joined: 09 Jan 2006
Posts: 290
Location: Seattle, WA USA

Posted: Fri Jan 20, 2006 2:06 pm Post subject: Plenum

Don,



I was hoping someone with more experience would have responded to your

question by now, but since I haven't seen anything, let me mention my

experiences to date:



I bought an expensive carbon-fiber plenum for my 0-360 and have spent months

trying to make it work. Most of the blame belongs with me; I seem to need to

build something two or three times before it starts to be acceptable.

Everything worked reasonably well until I got to the front inlets and

connecting the plenum up to the cowl. I totally rebuilt the front of the

carbon fiber plenum twice to get it to line up with the cowl inlets, then

ordered a new baffle kit from Van's and set the plenum aside as a maybe

winter project once I get this thing flying.



I have seen three general approaches to plenums in RV's. The first is the

Sam James composite plenum and cowl combination where the cowl inlets are

round and connect up with a flexible sleeve to the round inlets on the

plenum.  



The next approach is essentially to do the baffles but instead of doing the

flexible rubber seal from the baffles to the top cowl, cut down the baffles

and use either aluminum or composite to make a plenum out of the baffles.



The third approach I have seen is best shown my Mark Philips on his RV-6

website, which I can't find at the moment. I have also seen similar plenums

that come with a new Jaibaru engine from the factory. These are somewhat

distorted composite or aluminum tubes that run from the cowl air inlet over

the cylinders, one on each side. The bottom of the tube is open of course to

force the air down through the cooling fins on the cylinders. 



If I do another plenum, I will probably do the baffles, cut them down, and

then lay up a composite top that would fasten to the baffles on the sides

and back with piano hinges. I still haven't figured out how I would connect

it to the air inlets at the front.



Terry

RV-8A #80729, finishing (Whirl Wind 200RV prop came yesterday!)

Seattle

 



--

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Nuisance

Joined: 10 Jan 2006
Posts: 9

Posted: Thu Jan 26, 2006 8:55 am Post subject: Re: Plenum

Don, the easiest way for you to solve your CHT problems is to dump that LASAR system (excessive timing advance) and get Lightspeed or just plain magnetos. You can test this by removing power from the LASAR system when the engine is running too hot...you will reduce CHTs by 30 degrees as the timing reverts to baseline.



A plenum will help reduce cooling drag, but probably not make the engine run cooler unless you didn't fit your baffles well.



fun fun, John

[/quote]

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_________________
Life is too short to run lean of peak.

walter(at)tondu.com
Guest

Posted: Thu Jan 26, 2006 9:27 am Post subject: Plenum

On 01/26  8:55, aflyer wrote:



 > 

 > 

 > Don, the easiest way for you to solve your CHT problems is to dump that LASAR system (excessive timing advance) and get Lightspeed or just plain magnetos. You can test this by removing power from the LASAR system when the engine is running too hot...you will reduce CHTs by 30 degrees as the timing reverts to baseline.



The LASAR system will generally only increase CHT's by 15-20 degrees.



http://www.unisonindustries.com/products/lasar_installation/lasar_inst_seven.html

-- 

Walter Tondu

http://www.rv7-a.com

Flying!

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Nuisance

Joined: 10 Jan 2006
Posts: 9

Posted: Fri Jan 27, 2006 6:54 am Post subject: Re: Plenum

Walter, you can believe my testing, or their marketing fluff. 



I would often switch the LASAR off in a climb on a warm day, and even in cruise if it was warm at altitude, and if anything, 30 degrees is conservative. I am speaking from 150 hours experience with that system. During the second summer, I replaced it with dual Lightspeeds...problem solved. I have not seen 400 degrees since.



John

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_________________
Life is too short to run lean of peak.

walter(at)tondu.com
Guest

Posted: Fri Jan 27, 2006 9:03 am Post subject: Plenum

On 01/27  6:54, aflyer wrote:



 > 

 > 

 > Walter, you can believe my testing, or their marketing fluff. 

 > 

 > I would often switch the LASAR off in a climb on a warm day, and even in cruise if it was warm at altitude, and if anything, 30 degrees is conservative. I am speaking from 150 hours experience with that system. During the second summer, I replaced it with dual Lightspeeds...problem solved. I have not seen 400 degrees since.

 

Precisely why my P-Mags should be arriving in a few weeks!

I have examined everything I could related to the high CHT issue

and replaceing the LASAR system is next on the agenda.  I

certainly hope I see the same numbers you have seen.  Thanks

for the info.

-- 

Walter Tondu

http://www.rv7-a.com

Flying!

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