Okay, so I am going to make a new cowl-cover of an entirely different design that has built into it a "snorkel". I'm never going to do water-crossings, but I am using that term because people might be familiar with other similar projects. None, that I can find (for the XJ), make an entirely new cowl-cover though. Essentially, I want it to be just like the existing cowl-cover, but have a large airbox built into it that sits down into the cowl which is accessed from the engine bay, but I will also likely have it stick out the top some so it can take in more air. Basically, think of it like if you jammed the factory airbox down into the cowl and turned it's lid into an induction-scoop. It won't be 100% like that as I'm sure I'll have to adapt elements to solve particular challenges, but that's a good general idea.

Originally, I was going to have piping enter the box area and connect to a "can-style" filter like how most cowl induction intakes are done, but instead now I think I might have the airbox be an entirely sealed unit with a filter that sits in the top much like the OEM airbox. That way I do not have to worry about making the hole in the firewall air tight and can build it as 1 part of a larger carbon-fiber intake piping system.

They have all kinds of parts like this for Wranglers because you don't need to remake a large of a piece as for the XJs. There is actually a guy who has made something very similar to what I am talking about for Wranglers. I believe he owns Dinoot now. It's a red build that I belive is one of the early Gladiator kits, but I could be wrong about that. There was actually also a feature shown at I believe SEMA that was supposed to come on newer Wranglers, but got canned. None of these things are anything I could adapt over to work on a Cherokee except for general design ideas.

So, now here's my question. If a person is making a fiberglass mold from an existing product like the XJ's cowl-cover and is planning on essentially "cloning it" with just a big box inserted in a segment of it what would be the best way to go about this?

Should I buy another cowl-cover and cut a segment out and then fabricate a fiberglass airbox and stitch it all back together with fiberglass then make a 2 part mold from that part? Is there a better approach to this? Would it need to be made from an upper piece and a lower piece and glued together? Or maybe the segments wouldn't be "upper" and "lower" and instead should be the box and everything else? Basically, I am trying to get a fresh set of eyes to comment because you might mention something that I keep over-looking. I want to make the design around the best way to go about making this mold.

Couldn't it also maybe be done with a 1 part mold and laying the carbon fiber down into that? I really want to make this entire thing 1 piece out of the mold if possible. I believe this is possible. I am open to using fiberglass or carbon fiber with the final product, but I'd prefer to use carbon fiber. I am familiar with the vacuuming and bagging processes. This post is just referring to what approach I should take making the fiberglass mold, it isn't asking about how to do anything beyond that so lets not get too off-topic.

Please keep replies relevant only to making the fiberglass mold for this type of part. Design aspects that would dictate mold-type, filter type/size that might dictate mold-type, etc. As long as it is related to how the mold would have to be made. Hopefully that makes sense. Thank you.

 

I've done a lot of this kind of work, but it's hard to describe how to do it.

You need a draft (taper) on the mold so it will release. Usually around 15 deg in my experience, but people that do this for a living might use different standards.

As long as you have a draft, you can do either one piece or multi piece. Its easy to stitch fiberglass together, but hard to adhere different materials.

I usually use foam as a starting point for custom shapes but since you are working off of existing geometry, I like your idea of using an old cowl cover.

I would make a male "plug" then make a female fiberglass mold off of that.

1. Buy a used cowl cover
2. If you are "adding" geometry to it, make the protrusions out of foam (rigid foam insulation).
3. Cut the foam with exacto knife, bread knife, sand with a rasp and/or coarse sandpaper to shape. Make sure the shape has a "draft" to release the glass.
4. Glue the foam down to the cowl cover with something that won't melt foam. 5 min epoxy, construction adhesive, wood glue. Nothing in an aerosol.
5. Keep shaping it. Use drywall plaster to smooth it out. Skim the entire foam section in a thin layer of plaster - this keeps the resin from contacting snd destroying the foam. Get it PERFECT. Think it's good? Keep smoothing it.
6. On the seams where the foam connects to the cowl, make them smooth. Silicone the seams, or use tin ducting tape. You do not want the glass or resin to get into the seams or else it will not release.
7. Put either mold release on it, or wrap it in plastic wrap. Mold release is best.
8. Apply fiberglass to that. When making a mold from fiberglass use the finest weave you can.
9. Pull the glass off when cured.
10. Now if you want shapes that go the other way, like stick into the cowl, make those molds out of foam separately.
11. Repeat the above steps re: foam, plaster, fiberglass.
12. Cut a hole in your original glass mold and attach the second fiberglass part with fiberglass.
13. Bondo the seams and bondo Everything. Smooth it out!
14. Mold release the **** out of it.
15. Apply more fiberglass inside for your actual part, apply stiffeners out of the rigid foam or balsa.
16. Pull and release, then bodywork.
    
    The actual details really depends on you design. You might need two molds if you can't get a good draft. If you do that, make a flange where they connect. Then use plaster to fill in the seam between the two molds; the plaster will break apart when you pull the molds apart. But this keeps your final part as a single piece. Use strong binder clips or bolts to bolt the flanges together.

 

I haven't been on here in a while. Man, thank you for the reply. That is more or less exactly what I was thinking I had to do. I am going to reread your reply a few times though to make sure I didn't miss anything. I might PM you a question if that is okay. Just want to get your opinion about an aspect of the design.

 

Sure! My wife and I just had a baby a few weeks ago, so might not respond right away, but I'll try to take look at any PMs you send.

 

Ok, thank you. Congrats on the little critter.