Speed Cowl Inlets

[Walter Klatt]

Rick D., I was looking at your pictures in the file
section where you ramped your inlets. Did the change
also increase the inlet size, or do the ramps just
smooth flow? I couldn't tell for sure from the
pictures.

Walter



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[rebel]

Walter,
The actual openings get smaller but I think that the effective opening is
the same or greater(due to the smaller upper lip thickness). The actual
openings that I refer to and have just measured are, the left side is 3 3/4"
high (measured straight up and down at the rear of the opening) and 7" wide.
The right side is 3" high x 7" wide. I did not measure the original openings
but I think that they are 5" high x 7" wide. When I say "effective opening" I
mean, the opening size that will allow air to flow up and over the cylinders.
With the common baffling, the air looks like it will slam into the large flat
wall of the baffling and bounce right back out. Hence, I ramped the lower
inlets to smooth out the flow. The original upper inlets were cut off and I
thinned down the radius of those upper inlet lips and smoothly ramped back
about 7-8". I think that the vertical thickness of the upper inlet lip was 3/4"
to 1". It is now 1/2 - 5/8". Hopefully this will result in more effective
cooling. The left side provides cooling air for the oil cooler and the ramped
air looks to be a great improvement over the conventional approach. The left
side rises at about a 25* angle and the right side rises at about 45*. I would
have liked to have curled the right side up instead of just a straight angle
but that will have to be some other time. The engine baffling will pick up
those angles to keep the smooth flow. The plan is to put some silicone rubber
baffle material on the underside of the lower ramped inlets and let that rubber
sit on top of the metal baffles that are attached to the engine. I have also
fitted a front baffle seal behind the flywheel to keep the air in the engine
compartment. Just ask if you have more questions.
Good luck, you'll need it,
Rick D.
Rebel S/N 404R N754SM

On 6/22/2003 5:30 AM, WALTER.KLATT@SHAW.CA wrote to MURPHY-REBEL:

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-> Date: Sat, 21 Jun 2003 07:12:38 -0700
-> From: Walter Klatt <walter.klatt@shaw.ca>
-> Subject: Speed Cowl Inlets
-> To: Murphy-Rebel <murphy-rebel@dcsol.com>
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-> Rick D., I was looking at your pictures in the file
-> section where you ramped your inlets. Did the change
-> also increase the inlet size, or do the ramps just
-> smooth flow? I couldn't tell for sure from the
-> pictures.
->
-> Walter
->




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[rebel]

Walter,
I forgot to mention the modified cowl exits. If you look at the pictures
that I posted a while ago regarding the cowl exit you will see that I have also
modified the lower end to accomodate the exhaust pipes and clearance for the
heat cuffs. With both the inlet and exit mods I hope there will be no cooling
problems with this Rebel.
Rick D.




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[Walter Klatt]

Thanks, Rick, that confirms what I thought you did. I
did the same thing on mine, cutting back the lips and
ramping both the bottom and tops to smooth the air
flow. I have a lexan eyebrow on the left top inlet to
try and direct more air in. I also baffled off the
flywheel front so air can't escape there. At the exit,
I faired the bottom firewall flange with metal tape to
smooth the flow there. I think it all helped a little,
but the biggest difference was the bottom exit opening.
I saw what you did, and it looks very good. Now sure
how many sq in opening you have there, but I found size
does make a difference there, too, and of course shape,
like you have done. The only other considerations I see
in yours might be to add lips to deflect the air down
and to the side a bit and I saw a heat muff duct in the
opening that might impede air flow a little. You should
be able to change that by pointing the heat muff
openings up and route the duct a little higher.

Don't know if you were planning floats or not, but on
wheels, I think you should be OK. With mine, I had
initial problems on wheels, too, and then made
progressive changes until it was acceptable. Then I
went on floats, and my problems came back. I should
state that I'm talking about CHT's, and never did have
a problem with oil cooling. My oil cooler is attached
to the right rear baffle. Right now I am on about the
4th iteration of my bottom exit, and it's now about as
good as it is going to get. My cowl exit is big at
about 168 sq inches.

With my current set-up on floats, my CHT's (hottest on
back cylinders) run as low as 350 in winter and up to
400 in summer in cruise. However, in a heavily loaded
climb on a hot day, I have to do a pause when they get
up to 450, so I am still not totally satisfied.

My next step might be to raise the tops of the cowl
inlet openings to increase inlet size. That's why I was
asking about yours.

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
rebel@dcsol.com
Sent: Sunday, June 22, 2003 7:03 AM
To: murphy-rebel@dcsol.com
Subject: RE: Speed Cowl Inlets


Walter,
The actual openings get smaller but I
think that the effective opening is
the same or greater(due to the smaller upper
lip thickness). The actual
openings that I refer to and have just
measured are, the left side is 3 3/4"
high (measured straight up and down at the
rear of the opening) and 7" wide.
The right side is 3" high x 7" wide. I did
not measure the original openings
but I think that they are 5" high x 7" wide.
When I say "effective opening" I
mean, the opening size that will allow air
to flow up and over the cylinders.
With the common baffling, the air looks like
it will slam into the large flat
wall of the baffling and bounce right back
out. Hence, I ramped the lower
inlets to smooth out the flow. The original
upper inlets were cut off and I
thinned down the radius of those upper inlet
lips and smoothly ramped back
about 7-8". I think that the vertical
thickness of the upper inlet lip was 3/4"
to 1". It is now 1/2 - 5/8". Hopefully this
will result in more effective
cooling. The left side provides cooling air
for the oil cooler and the ramped
air looks to be a great improvement over the
conventional approach. The left
side rises at about a 25* angle and the
right side rises at about 45*. I would
have liked to have curled the right side up
instead of just a straight angle
but that will have to be some other time.
The engine baffling will pick up
those angles to keep the smooth flow. The
plan is to put some silicone rubber
baffle material on the underside of the
lower ramped inlets and let that rubber
sit on top of the metal baffles that are
attached to the engine. I have also
fitted a front baffle seal behind the
flywheel to keep the air in the engine
compartment. Just ask if you have more questions.
Good luck, you'll need it,
Rick D.
Rebel S/N 404R N754SM

On 6/22/2003 5:30 AM, WALTER.KLATT@SHAW.CA
wrote to MURPHY-REBEL:

-> Received: by dcsol.com (Wildcat! SMTP
Router v5.6.450.7)
-> for murphy-rebel@dcsol.com;
Sat, 21 Jun 2003 06:13:09 -0800
-> Received: from
shawidc-mo1.cg.shawcable.net ([24.71.223.10])
EHLO=pd2mo1so.prod.shaw.ca
-> by dcsol.com (Wildcat! SMTP
v5.6.450.7) with SMTP
-> id 45022125; Sat, 21 Jun 2003
06:13:08 -0800
-> Received: from pd3mr1so.prod.shaw.ca
-> (pd3mr1so-qfe3.prod.shaw.ca
[10.0.141.177]) by l-daemon
-> (iPlanet Messaging Server 5.2 HotFix
1.14 (built Mar 18 2003))
-> with ESMTP id <0HGU00EJE4ROWR@l-daemon>
for murphy-rebel@dcsol.com; Sat,
-> 21 Jun 2003 08:11:48 -0600 (MDT)
-> Received: from pn2ml6so.prod.shaw.ca
-> (pn2ml6so-qfe0.prod.shaw.ca
[10.0.121.150]) by l-daemon
-> (iPlanet Messaging Server 5.2 HotFix
1.14 (built Mar 18 2003))
-> with ESMTP id <0HGU00KAS4ROTX@l-daemon>
for murphy-rebel@dcsol.com; Sat,
-> 21 Jun 2003 08:11:48 -0600 (MDT)
-> Received: from user ([24.82.18.134])
-> by l-daemon (iPlanet Messaging Server
5.2 HotFix 1.14 (built Mar 18 2003))
-> with SMTP id <0HGU000M44ROJ5@l-daemon>
for murphy-rebel@dcsol.com; Sat,
-> 21 Jun 2003 08:11:48 -0600 (MDT)
-> Date: Sat, 21 Jun 2003 07:12:38 -0700
-> From: Walter Klatt <walter.klatt@shaw.ca>
-> Subject: Speed Cowl Inlets
-> To: Murphy-Rebel <murphy-rebel@dcsol.com>
-> Message-id:
<PFEOJDIIGOHLFACHDMDNEENACHAA.Walter.Klatt@shaw.ca>
-> X-Orig-MIME-version: 1.0
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charset=iso-8859-1
-> X-Orig-Content-transfer-encoding: 7BIT
-> Importance: Normal
-> X-Priority: 3 (Normal)
-> X-MSMail-priority: Normal
->
-> Rick D., I was looking at your pictures
in the file
-> section where you ramped your inlets. Did
the change
-> also increase the inlet size, or do the ramps just
-> smooth flow? I couldn't tell for sure from the
-> pictures.
->
-> Walter
->




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[Legeorgen]

Walter, Rick, Wayne and all,

I ramped my upper cowl inlets and flew today. It seemed to reduce my hottest
CHT in 75% cruise by 10* F. Now runs at 400* F after leaning. It was a bit
cooler today, but still...that's quit a drop and I'm pleased. I can reduce the
CHT's 10-15* F by not leaning.

I have already lipped the lower firewall and enlarged the cowl exit while
building (not nearly as large as you did Walter) and my next task will be to
install a baffle behind the flywheel. I'm hoping this will give me enough to be
sufficient on floats.

Blue skies and tailwinds,
Bruce 357R



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[Walter Klatt]

I will be interested in what difference the front
baffling makes. I had mine on since day 1, so don't
know how much it helps.

Best of luck with that, but I believe you will be
enlarging your bottom exit again before you're
finished. Just my prediction...

Walter

-----Original Message-----
From: mike.davis@dcsol.com
[mailto:mike.davis@dcsol.com]On Behalf Of
Legeorgen@aol.com
Sent: Sunday, June 22, 2003 9:14 PM
To: murphy-rebel@dcsol.com
Subject: Re: Speed Cowl Inlets


Walter, Rick, Wayne and all,

I ramped my upper cowl inlets and flew
today. It seemed to reduce my hottest
CHT in 75% cruise by 10* F. Now runs at 400*
F after leaning. It was a bit
cooler today, but still...that's quit a drop
and I'm pleased. I can reduce the
CHT's 10-15* F by not leaning.

I have already lipped the lower firewall and
enlarged the cowl exit while
building (not nearly as large as you did
Walter) and my next task will be to
install a baffle behind the flywheel. I'm
hoping this will give me enough to be
sufficient on floats.

Blue skies and tailwinds,
Bruce 357R



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