R

RV8R999

Well Known Member
In my continuous effort to experiment with cowl/baffle/inlets/exits to learn what works and what doesn't in controlling CHTs/OT and Cooling drag I was examining my baffling again when I noticed a huge air leak I hadn't seen before only it wasn't in my baffling it was the space between the cyl with dimensions of about .17" x 5.8" long for a total area of 1.97 sq in. (total including the other two cyl)

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wanting to fill this gap I bent two pieces of .02 alum 5.8" x 6" in half with a bend radius of about .2" for a snug but not too tight fit

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and gently tapped it into the space between the both sets of cyl thereby preventing any air from escaping through the gap and forcing the air through the cyl fins where it belongs.

2km0sn.jpg


There is another similar gap near the head of the two cyls about 1" long but recessed - I filled this in like fashion


The fit was snug enough Im sure it isn't going to come out but not so tight a piece of safety wire threaded under the bend and using a pair of pliers prevented removal.

Darn Florida afternoon thunder boomers preventing me from flying :(
 
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vibration

Danny7 said:
you are not worried about vibration wearing the metal?
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no not really as I do not believe much, if any, relative motion exists between each cyl but even so worst case would be for .02" total wearing off the edge of the cyl fins any more than this the baffle I installed would fall through.

We don't worry about the stock baffle material wearing near the rocker box covers do we? As far as I know the attachment holes do not elongate over time due to relative motion between cyl therefore i do not believe it is an issue.

It will be easy enough to check periodically to determine if they can be left in place.
 
So now we have heat being absorbed from the flat surfaces of the fins, but what about from the edges, as it's now blocked?

I haven't done any lab testing, to know the actual difference, though.
Just wondering.

L.Adamson
 
L.Adamson said:
So now we have heat being absorbed from the flat surfaces of the fins, but what about from the edges, as it's now blocked?

I haven't done any lab testing, to know the actual difference, though.
Just wondering.

L.Adamson
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Good point. Hopefully the increased mass flow along the greater area of the faces will offset the now blocked edges. I'm hoping for good Wx tomorrow AM to find out.
 
Somewhere I just read that you should not fill that space. If I can find the reference, I'll post it.
 
if you find something please post it.. I researched and could not find a reference other than opinion. Thanks!
 
really? Then how does the stock baffle material handle the relative movement without wear? The geometry of the standard baffle screw attachment points would certainly resist any motion between cyl and show elongation if this was occurring me thinks....
 
RV8R999 said:
really? Then how does the stock baffle material handle the relative movement without wear? The geometry of the standard baffle screw attachment points would certainly resist any motion between cyl and show elongation if this was occurring me thinks....
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If you look at the "Stock Baffle" material there is a slip built into the system between the cylinders. And, you will see some wear over time. I've seen it time and time again with plenums being fabricated cracking on the sides and top. I would just hate for someone to loose fins on their heads. :) YMMV
 
valid point about the Vans stock baffle, forgot about that slip joint (even though I was looking right at it for an hour yesterday).

Even so, the fit of these "shims" isn't overly tight and because the material is thin and flexible I don't think a fin could break. Possible to get some wear on the fin edges if the motion of cyl is significant enough I suppose. I'll watch it over time and see what happens. Heck...I don't even know if these will make any difference in CHT's. If they don't show a measurable result..they are out.

Thanks for info...
 
Each cylinder has it's own baffle piece screwed to the end of the cylinder. The pieces overlap each other and this allows for movement. If they were made of one piece of aluminum they would most certainly crack. After 500 hours I am getting some cracks on my solid aluminum plenum top where it attaches to these individual side pieces. This demonstrates the movement of the individual cylinders.
With what you are doing there should be no problem other then wear points on your insert. The 90 horse continental has a little insert exactly like what you have fabricated. It wraps a little around the bottom of two cylinders. It is held in position with a spring that attaches to a rod that goes between the cylinders.
I would like you to consider using it on one side of the engine only to see if a difference between the left and right side shows up.
 
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Cowl Exit

RV8R999 said:
I don't even know if these will make any difference in CHT's.
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After much research and some testing, I would guess you won't see much change in CHTs.

If you want to see a measurable drop in CHTs it may be worth checking the cowl exit area.
I opened ours 1/2 inch (increasing the cowl exit area by 6 sq inches) and got a 20-30 drop in climb and 5-10 deg at top speed. Test data from yesterday also seem to indicate about a 3 knot speed increase. This was our second step after opening up the carb jet one drill size from #42 to #41. Total CHT drop for the two steps 40-60+ deg. :D

Before these two mods, we always had to power back or the CHTs would sail through 450 deg like there was no tomorrow. :eek:
After climb CHTs for the hottest usually barely creeps past 400 and hasn't passes 430.

Another RVer looked into the same solution after trying about everything else ... and wrote it up here: http://www.mnwing.org/Sept2011.pdf (thanks John for finding it).
 
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