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11-09-2013, 04:37 PM
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Join Date: Feb 2005
Posts: 592
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SJ Cowl and Plenum
I will start fitting my Sam James cowl and plenum soon to my -7 and have some confusion on how the proper fit for the plenum around the front of the engine should look, especially the cylinders.
Does someone have detailed pics available I could review to hopefully find what I am looking for?
Thanks in advance,
Glenn Wilkinson
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RV-4 Sold
N654RV @ MLJ
RV-7 Coming Soon
N987RV Reserved
2015 Donation Gladly Paid
"Maintain Thy Airspeed, Lest the Earth Arise and Smite Thee"
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11-09-2013, 05:23 PM
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Join Date: Sep 2006
Location: Townsend, Montana
Posts: 3,179
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Fit the cowl first...forget about the plenum for now. Once the cowl is complete and the rings are epoxied in place, you can think of the plenum.
Now you can pull the upper cowl off and start working the plenum to the top of the engine. The plenum inlet must line up with the rings and the plenum top must have clearance under the cowl. Volume is your goal. I used the Vans Baffle kit and trimmed it to give clearance to the upper cowl.
My plenum fit poorly and I hacked it up pretty bad to clear the AFP FI spider and purge valve. also has to slice it so the front fit over the case properly and lengthen the inlets(i have the long cowl) Might have been easier to build a new one from scratch.
Here is the sized and painted but I had not finished trimming the baffles and drilling the sides for screws

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Retired Dam guy. Life is good.
Brian, N155BKsold but bought back.
Last edited by hydroguy2 : 11-09-2013 at 05:31 PM.
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11-09-2013, 07:35 PM
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Join Date: Mar 2005
Location: Olathe, KS
Posts: 374
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Plenum
One other thing on the plenum...don't worry about getting the front to fit around the engine curves. It is easiest to just hack it off, wax the engine case real well, then lay new glass between the plenum and the case.
Scott
7A
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11-10-2013, 06:36 AM
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Join Date: Jul 2008
Location: Sault Ste Marie, Ontario Canada
Posts: 236
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SJ Cowl and Plenum
Hi Brian, like you I've had to do a lot of work to get my Plenum to fit the way I want.
I've been thinking of extending the inlet tubes forward as well. How much of a gap did you leave between the metal rings and the Plenum?
Thanks, Terry.
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11-10-2013, 04:35 PM
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Join Date: Feb 2010
Location: Gardnerville Nv.
Posts: 2,828
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Don't mean to change the subject but since you are here and I'm not, I have a question about the SJ Cowl, how much did you have to trim on the firewall side, someone one here spaced his engine mount 5/8 inch to move CG to compensate for a FP prop, is there plenty for this?
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7A Slider, EFII Angle 360, CS, SJ.
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11-10-2013, 11:05 PM
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Join Date: Feb 2005
Posts: 592
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Brian et al,
Thanks for the info on how to best get started and I'm sure I'll be back with more questions in the future.
You've been a big help.
Glenn Wilkinson
__________________
_____________________________________________
RV-4 Sold
N654RV @ MLJ
RV-7 Coming Soon
N987RV Reserved
2015 Donation Gladly Paid
"Maintain Thy Airspeed, Lest the Earth Arise and Smite Thee"
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11-11-2013, 10:26 AM
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Join Date: Sep 2006
Location: Townsend, Montana
Posts: 3,179
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Quote:
Originally Posted by bret
Don't mean to change the subject but since you are here and I'm not, I have a question about the SJ Cowl, how much did you have to trim on the firewall side, someone one here spaced his engine mount 5/8 inch to move CG to compensate for a FP prop, is there plenty for this?
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Bret, It depends....does that help?
no really it depends on what cowl you got, what prop spacer you got, etc.
I have a IO-360 parallel valve, WW200RV prop and 2.25" Saber spacer. I also have the James Long cowl for my -7. I trimmed off between 1"-1.5", if I recall.
If you have the short cowl version, I think it work with no spacer, but probably trimming the same amount....i think. Chad Jensen used a 320 engine mount with his 360 and a spacer with his Catto prop, but had James build him a custom length cowl.
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Retired Dam guy. Life is good.
Brian, N155BKsold but bought back.
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11-11-2013, 11:57 AM
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Join Date: Dec 2005
Location: Mahomet, Illinois
Posts: 2,195
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Quote:
Originally Posted by hydroguy2
If you have the short cowl version, I think it work with no spacer, but probably trimming the same amount....i think. Chad Jensen used a 320 engine mount with his 360 and a spacer with his Catto prop, but had James build him a custom length cowl.
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I have the long cowl with a Catto 3-blade ...it required a 4" prop extension. It was my understanding the short cowl (with a FP prop) gets the 2 1/2" extension.
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Terry Ruprecht
RV-9A Tip-up; IO-320 D2A
S. James cowl/plenum
(Dues paid thru Nov '18)
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11-11-2013, 12:18 PM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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I have the short cowl and you really don't know how much you need to trim until the engine and prop are in place. Once they are, set the top cowl in place and work from there.
Regarding the cooling plenum, I put mine fairly low, which was a good thing.
Two tips for you:
1. Reinforce the section behind #4 cylinder with some .063 AA. You will have to file off the point of the angle to get it to nestle in there. That will keep the baffles from cracking.
2. Slather the front of your engine with mold release (I used vaseline.), cut off the forward lip of the plenum, lay fiberglass over the front of the plenum right on the engine. That will guarantee you have a good, leak free fit.
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Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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11-11-2013, 01:59 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by N941WR
2. Slather the front of your engine with mold release (I used vaseline.), cut off the forward lip of the plenum, lay fiberglass over the front of the plenum right on the engine. That will guarantee you have a good, leak free fit.
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I notice you guys don't bother with fasteners across the front. It's difficult to imagine a good leak free fit along an unsecured edge when the lid is being pushed up by significant internal pressure.
At 180 knots and 3500 feet, even a James setup will load the plenum lid at 60 lbs per sq foot, the delta between plenum pressure and cowl pressure. You have 3 sq feet (or more), thus 180 lbs on a box lid with no fasteners across the whole front span...maybe 18"?
Need a familiar illustration? When we space fasteners 3" apart across the top center of a standard Vans cowl, out in front of the windshield, we can watch it bow up between them in flight. That's in response to lower cowl internal pressure, in this case about 20 lbs per sq ft. Sure, more area, but if the upper cowl has 3 times the area of a plenum (which can't be far from true), it is an apples-to-apples comparison.
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Dan Horton
RV-8 SS
Barrett IO-390
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