FAB Notched Seal?

[Bayou Bert]

I am having trouble seeing this in my head from the Vans instructions on mating
the cowl to the air box. I have the fiberglass tunnel built that goes
right to the FAB intake. I understand putting the seal around the
outside? Seems to me the seal will be blown back by the air coming
in the scoop, just don't understand how it will seal.
Vans says to notch the seal, does that mean cut slots in the rubber, where?
Then it would leak even more seems to me.
Sure would appreciate someone that can set me and my head straight on
this so I can move on with the project. I have been debating with myself
for two days now.

[brad walton]

There should be a better way. But there is relative motion between the FAB and cowling inlet that prevents getting the kind of airtight seal I would like to have there. The engine moves a good bit, especially on start up and shut down. I suspect there is not much presure loss anyway.

[Rick_A]

You need some space between the FAB and glass tunnel. Not only for the relative motion as previously noted but also because you will have one heck of a time removing and re-installing the cowl - which you will do often - without a flexible interface between the FAB and tunnel.

The notches in the baffle material go where it attaches to the FAB. The the part that interfaces with the tunnel is continuous. I did mine in 2 pieces that overlap. The bottom part covers the bottom & sides. The top piece does the top only.

[Bayou Bert]

Thanks Brad and Rick. I do have about 1/4" gap between glass and
the FAB. Got to thinking and I guess there is a heck of a suction there
before you start moving and by so ramming air into the scoop.
Wonder if the pressure at inlet of FAB ever gets positive or does the engine
needs stay ahead of the ram air? This makes sense as to why seal is on the
outside. I was careful not to reduce the area of the scoop opening. My FG
tunnel is a lot wider than the cowl opening by the time it gets to the FAB,
so no reduction. Rick, so only slot in rubber is the top two corners where
the two seal pieces meet up....right?

[bhester]

You can see my seal in some pictures at the bottom of this page.
http://home.newwavecomm.net/bobbyhester/RVSite.htm

Two pieces one around the fiberglass and one on the top.
After installing the Lwr cowl you usually need to push the seal into position.

[noelf]

I sort of remember this from my build.


Once the FAB box is together attached to the carb, and pointed toward the air scoop opening of the lower cowl...

First is to use the foam plug trick to fiberglass an extension to the cowling air scoop. When finished, it should end with a 1/4 to 3/8 inch gap between it and the front of the FAB opening.

The rubber gap seal material will be attached to the FAB front opening. Form the material into a "U" shape with the opening at the top. The sides of the "U" will extend up beyond the side of the FAB some. The amount of this U that you choose to extend forward of the FAB will form a "cradle" around the outside of the extended fiberglass tunnel of the air scoop

Once you are satisfied with the fit of the cowling, FAB box, tunnel, and gap seal so far, and you see how the lower cowling can be raised in place and lowered for removal, then you can cut and position the last piece of gap seal on the forward upper lip of the FAB. It will be trimmed so the forward edge of the gap seal just touches the aft top edge of the fiberglass tunnel.

You can now turn up the outside edges of this top seal so that they lay inside the extended "ears" of the big "U" that you first attached to the FAB. Secure these two extensions together and this will keep the top gap seal from blowing out with your expected 200mph ram air speed.