REFLECTOR:Baffling, CHT, EGT, Ehxaust Wrap ...

[Scott]

Jim,

Have you read "The Pelican's Perch" articles about LOP operations? If not 
they are a must, very detailed, very informative and all from real data 
collected by GAMI and by Deakin.  Here's a link to one of his articles on 
Avweb,  http://www.avweb.com/news/columns/182179-1.html   There's lots more.

The temps of you EGT and CHT's is not linear its more like a hill.  You are 
running on the rich side of the hill, probably 50 to 150 ROP, as you lean 
the temps will rise until you reach peak, then they will come down.  But 
you have to get past PEAK.  If your engine is carburated you can't do 
it.  If your engine is injected with factory injectors you "might" be be 
able to do it.  An EI will help you get really lean, quite a bit.  With my 
IO360 with stock injectors and two mags, I couldn't lean to 50 LOP, after 
installing the light speed I can now lean to 100 LOP if all my plugs are 
pretty clean.  You might have to get Gamijectors to run LOP.

So if your just leaning to PEAK and not 50 LOP your CHT's will be much 
higher. Which is what I suspect is happening.  Are you sure your at least 
50 LOP when you see the temps rise?  When experimenting and learning about 
LOP be sure to do it at 8000 ft or above so you don't have to worry 
about  detonation problems.

As far as the exhaust wraps, I tried em and they didn't help at all.  If 
your pipes are made of "really good" stainless, they probably won't hurt, 
if not they will corrode  very fast from the heat and moisture cycle. Tight 
baffling is the key as you are finding out.

Scott

At 10:09 PM 11/9/2003, you wrote:
>Hey guys,
>I've got a puzzlment here.
>My Velocity (173 FG) came at me pretty much fuel cooled.  CHT
>went up really fast if I leaned off of full rich at all.
>Baffling had gaps you could throw a cat through, crummy tin gap
>fillers between the barrels, no attempt to seal up the exhaust
>pipes at the cowl nipples, etc.
>
>Finally a friend grabbed me by the stackin' swivel and read me
>the riot act about lead deposits in the chambers, etc. and made
>me do the math (I'm spending about 45 to $9 per hour extra on
>fuel).  That last did it.  Wish I'd done it MUCH sooner.  ALWAYS
>do the math :-)  Much as I hate baffling, I tore it all out and
>did it over, improving bulkhead around alternator and starter,
>etc.
>
>Anyway, with BID-RTV around and between the barrels and tight
>seals elsewhere (except the exhaust pipe wasn't sealed that
>well) I tried it out.  I could lean somewhat better, but no
>really dramatic improvement.  Leaning still caused CHT to rise
>quickly.  I knew I had a lot better sealing of the plenum, and I
>intuited that the exhaust pipe not being sealed would affect #1
>& 3 more than #2 & 4 but that was not the case.  But that was
>just a guess.
>
>So ... I sealed up the exhaust-cowl gaps really well.  I figured
>that would trap all the heat that the breeze out the pipe-cowl
>gap had been carrying away and significantly pre-heat the
>cooling air going to the cylinders, so I wrapped the exhaust
>pipes (I've heard this can aggravate if not cause cracking of
>the pipes and hide the cracks until something breaks, but I
>thought I'd try it for a while).
>
>Weird!  Where before I had maybe 1 or 2 "ticks" of EGT on the
>Graphic Engine Monitor before the CHTs started getting away from
>me, suddenly, I've got 3 tics on TAXI.  On climb out, the CHTs
>still get high, but the EGTs are higher than I've ever seen.  I
>figure the EGT got way high because I'm retaining all that heat
>that used to escape through the walls of the pipe and it's
>driving the EGTs up. Waaaay up.  But why do the CHTs go up too?
>There's no more leakage, the pipes are wrapped so the cooling
>air isn't preheated the way it was.  What's the problem?
>
>The only thing I can come up with is that the high EGTs are
>making the pipe really hot and the hot pipe is heating the
>flange and the CHT probe is close to the exhaust flange.
>Problem is, the airplane is updraft and I'm measuring the temps
>on the "cool" (upstream) side and I don't know what they are on
>the top of the engine.  I used to have a plug gasket CHT probe
>that I could replace one of the bayonet probes with and move it
>to the top of the engine to see what the delta T is across the
>head, or at least across the plug positions.  Hope the wire is
>long enough to reach the box where the trick wires terminate.
>
>Any explanations for what's happening to me are most welcome ...
>Jim S.
>
>Jim Sower
>Crossville, TN; Chapter 5
>Long-EZ N83RT, Velocity N4095T
>
>
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