Air box fabrication

[gboone]

I'm looking for some advice on either having a cold air box fabricated or fabricating it myself. I'm trying to mate this new box to a pair of side draft throttle bodies retrofitted to a 4 cylinder engine, and have a 3" diameter tube on the front of the box for a filter in front of the engine. Due to space constraints, the box will need to have some 3 dimensional curved surfaces, so I'm thinking of fiberglass or some other plastic. Can anyone recommend a fabricator or an instructional publication to steer me right? I have no experience with something like this. :confused: :o
Thanks for any tips.

[jhadler]

Gary,

You could make your own out of fiberglass. Make a mold shape out of styrofoam, and then lay the glass over it. It doesn't have to be strong right?

I'd hate to think how much it would cost to pay someone else to fabricate that...unless there's already one out there...

-Josh2

[Built-By-Bones]

Josh is correct, you could attempt this project yourself.

Having a pro do this would likely be more expensive than your budget allows. We no longer work in f/glass but our 2006 shop rates for carbon work are $110/hr plus materials :eek: A typical airbox will take 8 - 12 hrs depending on complexity and materials.

If you use styrofoam to shape the intake, make sure you use an epoxy resin when laying up the f/glass. Normal poly resins will eat into the styrofoam. If you do this yourself, expect that it may take two or three attempts to get it right. Even amongst the pro's there is a high rate of failure on custom one-off pieces. Consider each failure a learning experience, I have been involved with composites for 28 years - I built my first surfboard at 12 - and we still experience failure every so often. It's just part of the business.

Some basic tips.

- make a plug of the part you need. Surefoam (similar to the blue foam at Home Depot) and Bondo work well.
- once you have a final shape, clean the surface (Xylene) and then apply at least a dozen coats of wax (turtle wax with carnuba).
- make a mould of your plug. For one off's, plaster of paris moulds will suffice. The Exon Epopast system is great for low volume moulds, if you intend making more than one piece (but less than 25 pieces)
- remove plug from mould.
- repair and prepare mould. sand entire mould starting with 150 grit and working up to 600 grit wet.
- wax mould at least a dozen times (if using plaster of paris) or 6 times if you are using Epopast. Spray mould with a release agent (polyvinyl) if available.
- apply gelcoat to mould, let it dry just beyond tack dry. apply first layers of glass (usually a very fine weave). Apply additional layers of material, if using carbon apply as spec'd by your designer. If using f/glass, E-glass is preferred but f/glass matt will suffice. This is a wet layup, make sure you roll the f/glass to remove any trapped air (this causes voids, which are weak spots and the start of delamination)
- remove from mould, clean, sand and prep for paint.

Most likely for an intake box you will need to make your mould in two pieces. You can choose whether you want to make your intake in a single piece (difficult) or in two seperate pieces that you then bond together (easier).

There are some excellent books available on the subject - one author I'd look for is Forbes Aird (sp?)

Not an easy task, but very satisfying once you get it right.

HTH
Bones

[peterraymond]

Gary,

If you are really only making one of these there is what might be an easier way, but the result won't be as pretty. Make the initial shape out of foam, like the stuff at home depot, or packing material. Get the surface as smooth as you can. Fiberglass over the top with epoxy, as was mentioned. Next use gasoline or some other solvent to melt out the foam. What is left is your final product. You can spray paint it, or you can add pigment earlier in the process. I would recommend spray paint though since it lets you see and get rid of air bubbles as you work. When you are done you can bondo the outside and do some sanding to improve the appearance of the final product.

You also need some way of connecting the box so you can get it on and off.

Peter Raymond

[BoulderG]

I'm ignorant -

Why is it so extremely important to make the mold surface as smooth as possible?

Particularly for an airbox, I wouldn't expect airflow/laminar/turbulence issues.

Is it something to do with working the fiberglass?

Thanks...

[Built-By-Bones]

The mold surface needs to be as smooth as possible so that the part will release from the mold.

The reason there is so much sanding involved is to create a surface that the wax will stick to. Sand the mold with increasing finer grits to 600 or so. That feels really smooth to the touch, but on a microscopic level, there is a lot of surface area for the wax to penetrate.

Kinda like a reverse procedure to getting f/glass to bond to anything. You usually roughen and chamfer the surrounding area so the f/glass can bond properly to the substrate. By making the mold super slick and smooth we can hope that the finished part would release with ease. Not always, but hopefully mostly.

Mold design also plays a large part, no undercut surfaces, no lips, no complex multi-dimensional surfaces. Not something easy to describe, but usually learnt from experience.

Clear as mud?