Custom Super Snake Hood. Need ideas

[Otee453]

I have a custom’ish super snake hood that I’m doing. It involved bonding an inner and outer layers into the proper MKIV curvature, which I’ve done. Now I have a relatively unfinished underside of the scoop.

As can be seen in the pictures, there is a gap between the inner and outer fiberglass and the underside of the scoop is unfinished (lacking gel coat) fiberglass. My understanding on the old roadsters with a fiberglass scoop, people finished the raw fiberglass with body filler. That’s my plan here too.

What my idea is to finish the gap is to slowly & carefully fill the void with expanding foam, leaving a half inch or so from the edge to bridge the gap with HSRF. The foam would essentially only create a backing for filling & finishing with HSRF and the skim coat a final surface with body filler.

Any other ideas to cosmetically fill or bridge the gap between the layers? Yes, I could leave as is but it really would be a bit hackish leaving it that way.

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[phileas_fogg]

I would be concerned with containing the expanding foam so that it doesn't make a huge mess, and would ask a boat guy (GoDadGo comes to mind) about what he'd do.


John

[Otee453]

I would be concerned with containing the expanding foam so that it doesn't make a huge mess, and would ask a boat guy (GoDadGo comes to mind) about what he'd do.


John

Exactly my concern too. I’m going to try styrofoam cut into strips and shaped appropriately to try stuffing that in there to act as a backing for the HSRF. Styrofoam, if it doesn’t work will not cause the mess and problems spray foam would.

[j.miller]

Exactly my concern too. I’m going to try styrofoam cut into strips and shaped appropriately to try stuffing that in there to act as a backing for the HSRF. Styrofoam, if it doesn’t work will not cause the mess and problems spray foam would.

That is what I would do. A soft material just as a stop-gap for the hsrf...da Bat

[J R Jones]

In my experience polyester eats pink foam, I am not positive about styrofoam, but I think that is at risk too.
Blue foam (art supply store) is OK, and I think epoxy resin is OK.
Expanding foam may spread your surfaces as it cures. The core of expanding foam is long cure, it stays liquid.
An alternative MIGHT BE black plumbing insulation foam tubes. Test for compatibility.
I use epoxy and panel bonder exclusively. Better physical properties.
jim

[i.e.427]

From someone that has done this, forget the foam. Get some glass cloth, cut it in strips wider than needed and some fiberglass resin. Bridge the gap with the fiberglass and once you're satisfied with the rough contour start in with your body filler. If you keep the body filler minimal in thickness, you can forego the HSRF. I have pictures somewhere. I'll see if I can find them.

https://thefactoryfiveforum.com/attachment.php?attachmentid=153271&d=1631423699

[J R Jones]

From someone that has done this, forget the foam. Get some glass cloth, cut it in strips wider than needed and some fiberglass resin. Bridge the gap with the fiberglass and once you're satisfied with the rough contour start in with your body filler. If you keep the body filler minimal in thickness, you can forego the HSRF. I have pictures somewhere. I'll see if I can find them.

https://thefactoryfiveforum.com/attachment.php?attachmentid=153271&d=1631423699

i.e. I use preformed FRP sheet and tubes, cut to fit and bonded in place. I have made made major body sections this way, including bending thinner sheets in simple curves to fit an armature.
jim

[NC Cobra]

[QUOTE=Otee453;468448]
“As can be seen in the pictures, there is a gap between the inner and outer fiberglass and the underside of the scoop is unfinished (lacking gel coat) fiberglass. My understanding on the old roadsters with a fiberglass scoop, people finished the raw fiberglass with body filler. That’s my plan here too. Any other ideas to cosmetically fill or bridge the gap between the layers? Yes, I could leave as is but it really would be a bit hackish leaving it that way. “




Really you have two issues here to be addressed. In my opinion, having done too many sail boat bottoms to count, you do not want to use filler to span a relatively large gap such as the one you have your finger inside of in one of the photos. Given time the twist and vibration will point load a section and you will have sections of the work break away. As described elsewhere, a better way would be to run a piece of 1.5” glass tape along the gap making sure to keep roughly equal contact patches on both contact surfaces. The radius of the corners by the firewall may be a bit tight for a single piece to wrap around so consider doing that section with separate pieces of tape. Try it first with blue painters tape and you will be able to get a feel for how much of a bend the fiberglass can accomodate. BTW, I highly recommend that you avoid cutting your own tape and stick to the pre-sized rolls. The bound edge of the tape is your friend and trust me you will spend much more in sand paper cleaning up you work than the initial outlay for the right product for the job.

As for the underside of the scoop, I would lay down a coat of resin to seal the surface and provide a common bonding surface and then smooth out the imperfections with a soft filler compatible with the resin you used to seal it. Remember, you can use epoxy over polyester but not the other way around. Once cured, sand away till you are happy with the surface and then either paint or gel coat the surface as you see fit.

As for products, I would recommend West System epoxies and fillers. The Gougon brothers really know there stuff and I’ve never had a problem with their products over decades of use. A good place to track it down is a marine store. The big box locations like West Marine are your best bet and can provide a one stop shopping experience for the whole job - at least in pre-pandemic times.

Good luck on the project and hope you have a better experience than Bill Cosby with his Super Snake. (assuming you going with a blower for the engine, hence the larger air intake)

[rich grsc]

Another idea is to use thin strips of balsa wood. Insert between the upper and lower panel to get a consistent gap, hold them in place with CA glue. Use narrow pieces of balsa, spaced around the opening. Then fill the gap between the panels with HSRF.