How do you attach a fiberglass hood scoop?

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In the eighties the product I used to attach fiberglass to bare metal was called "cathair" it was a body filler with fine strands of fiberglass mixed into it, you mixed it like bodyfiller with a tube of hardener. It worked well and bonded the two very well.
There maybe better products around nowadays, checkout eastwood.com I'm sure others will chime in as well.
 
since you have the bond on type of scoop, there are two good ways to bond it to the hood. first prep the surfaces properly. the first way you use epoxy to bond the scoop to the hood, then when the epoxy has set up, you smooth the excess epoxy off, then go over the seam with body filler, the cat hair stuff works great. smooth that down until you are satisfied with the effect.

the second way you set the scoop in place, and drill several small holes for pop rivits, then after the rivits are installed, you go over the seam with body filler again to smooth everything out.

you can also use rivits with epoxy and body filler if you like. remember you dont want the hood scoop coming off while diving down the road.
 
Best way is to get a scoop that is made to bolt on.

Though you can bond fiber to a steel hood, most professional custom body guys won't do it.
I know a man that builds 6 figure rods and he refuses to mate fiber and steel by bonding them. He says it WILL crack and warp. His reputation is worth far more than anyone can pay him to do this. Vibration and weather react differently with fiber and steel, so to put the two together will crack/break the bonding medium... no matter if this is epoxy or tigerhair or whatever.

So, bolt it on, or don't do it is what the pros say.

Edit:
If you have a fiber hood, that is a different story!
Bond on scoops are made specifically for fiber hoods.
 
there are automotive epoxies made that are oem approved for bonding plastics (fiberglass falls into this catagory) to metal. when you come right down to it, using polyester fillers on metal is the same as bonding plastic to metal, they both expand at different rates, right?
 
when you come right down to it, using polyester fillers on metal is the same as bonding plastic to metal, they both expand at different rates, right?

You mean Bondo...

I see cars all the time with Bondo falling off under the paint.
My son's car has a bondo repair on the rear quarter, just behind the driver's door that is all jacked up under the paint. Looks nasty, just like it does when the bonded on hood scoop cracks up the paint and gets all jacked up the same.

I am sure everyone here has seen Bondo under cracked paint, well every bonded on scoop I have seen is like that too. (unless it was just done, or a garage/trailer queen)


Edit:
I am not going to get into a pissing match with pro-bondo folks.
Just pointing out the obvious, and now I am done.
Do it the way you like.
 
OK,

First, I am totally not above using elmers glue on this :D If you recall, I am one of the "Paint your car your self w/ rollers for $100" guys. (Worked great by the way)

so I placed the scoop on the hood traced it w/ a marker
took a dremel and all around the inside of my trace line, I cut little 1 cm lines into the paint to the metal so it looked like a dotted line tracing the scoop.

Ran a thick bead of epoxy around the dotted line ensuring that it got in to those dremel crevices real good. Put the scoop down and put weights all over the thing.

I just added some body filler to the seam. I think it is going to look good. Not going for a show car here just a car that sits in my garage and only cruise around the neighborhood a couple times a year.

Now I got to get the rollers and rustoleum back out and re work the hood a bit. :D
 
I did kitty hair, rivets, a layer of fiberglass mesh and then a bondo treatment to bond and smooth a Shelby fiberglass scoop to my metal hood in 1978. After thousands of miles (local and cross country) and 80 or so drag runs this year, it still has yet to crack. My engine bay gets quite hot with the 1 3/4" headers on the windsor.

The hood is very, very heavy though. . . . . .

With a roll on paint job, I wouldn't think twice about adding the scoop as touch ups are well within your capability.