New build upcoming - questions on fiberglass and vinyl and foam

Ok, so... going to finally gut the hatchback in the Z and replace it. Going to build some fiberglass enclosures for a pair of 12s. I expect I'll be doing 2 separate enclosures, one for either side, but it's possible I could end up with a single enclosure up by the seats, with subs firing backwards or upwards. I haven't decided yet.

Anyways, I built a fiberglass sub box once, years ago, in my 240sx. I just can't remember what all I used, in terms of how much material.

Fiberglass stuff will come from US Composites, which I think is still probably the best place. Looking at maybe 3 yards of 3/4 oz chopmat, and 7 yards of 1.5 oz chopmat. I also think I have a few yards I never used up in the attic - should still be good, right? Can't imagine any problems with it, but I did discard the old resin years ago. 3 gallons of 435 polyester resin should be plenty, right?

I am really just totally guessing here, I have absolutely no idea. I'll likely be doing the first layer with fleece, then building on that. Last time, I laid down the back side of the sub box, which conformed to one side of the hatchback, got a couple layers, then pulled it out, trimmed it up with a Dremel and laid down more layers to thicken it. Then I took wooden dowels and cut them to length, hot-glued my mounting rings in position, stretched my fleece over it all and then glassed it all up. This time I was wondering about trying something different...

I remember seeing a video where someone took large pieces of foam and used them to make mock shapes, then 'glassed over them and used something later to dissolve/melt the foam to get it out of the new fiberglass enclosure. So I could get some hard foam that was amenable to shaving/molding, put a rough shape to it, fit it in position in the hatch, then take it in and out while shaving small amounts off to mold it into what I want - then fiberglass over that and melt the foam out later. Is this a decent option? Or am I better off using small thin wooden strips and dowels to make a rough skeleton and stretch fleece over it like I did years ago? It's going to be a pretty complex box shape, I guess.

The more I look at things, I think I'm going to probably end up with a larger, ported enclosure for these Mag V3s... so that's going to impact things.


I guess that's it for now, I'll be doing more research over the next few days. Install will be right in the middle of May - about 10 days from now.

Any suggestions appreciated.

Go with what you know and fire em backwards!

on a hatch, firing up works wonders but so does firing towards the back. done both ways, but feel upwards due to the reflection of the rear window works best..

This sounds like its going to be a total learning experience. I hope you take tons of pics and give instructions as you go if you do the foam route!

Glass is pretty fun to work with. I've done that dual 12 sub box and done kickpanels in the past. Problem is just remembering how much to order. Too much is, of course, better than too little.

Ok, well, I took the plunge.

3/4 oz chopmat - 8 yards
1 1/2 oz chopmat - 4 yards
polyester resin - 3 gallons
extra MEKP - 16 oz
Box of 1.5" brushes
Pint and quart mixing cups

Gonna be a grand old time! :D I'll make sure to do a build log with lots of pics.

I'm nervous as a long-tailed cat in a room full of rocking chairs to undertake this!

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Originally Posted by tRidiot

I remember seeing a video where someone took large pieces of foam and used them to make mock shapes, then 'glassed over them and used something later to dissolve/melt the foam to get it out of the new fiberglass enclosure. So I could get some hard foam that was amenable to shaving/molding, put a rough shape to it, fit it in position in the hatch, then take it in and out while shaving small amounts off to mold it into what I want - then fiberglass over that and melt the foam out later. Is this a decent option? Or am I better off using small thin wooden strips and dowels to make a rough skeleton and stretch fleece over it like I did years ago? It's going to be a pretty complex box shape, I guess.

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Polystyrene will dissolve with acetone, unfortunately polyester resin will also dissolve it (but not epoxy). You'll need to cover it with thick foil or some other barrier, and once the fiberglass has hardened, you can use acetone to dissolve the plug.