cnapi001

I'm in the process of building my own rear diffuser, modeled loosely on the top secret/voltex designs. In addition, the diffuser will extend well past where those diffusers go underneath the car, all the way to the gas tank/exhaust and driveshaft tunnel.

For the visible portion of the diffuser, I'll be making it out of fiberglass, using 8.7oz 2x2 twill glass (not carbon fiber), carbon fiber tape (for the seams/edges), and epoxy resin. The end result will be opaque gloss black using resin dye. To provide structural strength and aid in layup of the glass and resin, the diffuser will be made using a 1/8" hardboard "skeleton" as a core. Basically, I constructed the entire diffuser out of the hardboard and wood glue, and then cut out large sections of the panels to reduce weight so that all thats left is a one inch wide frame.

Couple of questions for you guys though. I'm not using carbon fiber cloth because its just ridiculously expensive and harder to work with than glass. How many layers of 8.7oz cloth/resin do you think are neccessary to give it enough strength for rock and gravel hits on the highway. Keep in mind most of it will not have the wood as a core, and will just be glass and resin.

Second question: underneath the car, for the portion of the diffuser that extends from the muffler to the gas tank will be a simple flat panel, I'm planning on just buying a large plastic sheet and cutting it to shape. Anyone have any cost effective suggestions on what type of plastic? Keep in mind the exhaust midpipe will be in very close proximity, if not in contact with the plastic. I was thinking premade 3/16 inch electrical grade fiberglass (GP03) from McMaster-Carr. Its light weight rated at 0-289 degrees fahrenheit, 300 max. Maybe even use some carbon fiber insulation tape on the plastic (its fairly cheap and rated to protect against up to 700 degrees)Also, what kind of plastic is the OEM undertray and other plastic bits made out of, does anyone know?

Al Kapwned

check this site out. It should help you a lot.

http://fiberglassforums.com

Zazz93

iTrader: (2)

I've been toying with the idea of learning and trying to work out a diffuser but it just seems out of reach until I really learn how to work with fiberglass. Best of luck!

cnapi001

Thanks!

As a word of encouragement, using fiberglass is actually fairly easy. Start small. I learned by doing some research and starting with making new speaker grills. Once you get the hang of it, you can fabricate pretty much anything.

Once I get a few more details worked out (mainly the minimum amount of fiberglass and resin I can get away with to keep weight down), I'm going to post the whole process of how I did it with pics of each step and how it turns out if you're curious. I'm planning on starting in a week or so.

aaronz8

good luck! i'm curious

Juice+

Any updates OP?

Archaismic

iTrader: (5)

i've done a lot of composite work esp w/ FG. if you're doing an under car thing i'd say 2 layers of FG and then rhino line it... you might even be able to do one layer if you make the fastening areas stronger since FG is decently flexible it can take pretty decent hits and not break but it'll wear down eventually if you don't either build it up or coat it with something... to keep the weight down just do as many layers as it takes to make sure there aren't any holes in it (2 like i said before should be good but you can try one and see if that does it). the rhino liner or other undercarriage/truck bed liner has enough elasticity to deflect pretty much any rock damage that would occur under a car

hope that helps and good luck... i've been thinking about doing the same to my z but i have to fix the body kit first

Archaismic

iTrader: (5)

ohh and the plastic thing... what i was going to do it get some lexan from lowes or the like and take a heat gun to it to shape it around everything i could then where it was too complex add some FG... as for the heat issue i've been running into the same problem... what i eventually picked up for it (but have not verified) is refrasil cloth... it's a really heavy duty FG cloth made for protecting surfaces from welding slag and such i was going to fold it over the lip of the hardened area applying resin up to within about an inch of the heat source (exhaust) and let the cloth actually contact the exhaust. i think with it being doubled over it should be nice and smooth against the exhaust to close air gaps, allow it to vibrate like exhaust does and it should be plenty of heat dissipation to prevent it from overheating the diffuser structure...

that's what refrasil cloth looks like

it's just a FG weave fabric... really heavy though

that's kinda the setup i was thinking of doing it's doubled over the ledge of the structure (black thing) and actually rubs up against the pipe
obviously you can do a lot better with the wrap and such and clean up the edges... i just mocked it up to show what iw as talking about

cnapi001

No updates yet. Just finishing up the frame. FG supplies are on order, waiting for them to arrive. I'm using a thin epoxy resin with a mixture of glass and some carbon fiber cloth.

Thanks for the advice on the layers. I was thinking two as well. I've decided on a 2x2 twill pattern glass cloth, and narrow strips of carbon fiber to reinforce the joints/seams. The seams will have 3 layers, the majority of the rest 2 layers.

For the bottom I've decided to go with aluminum to avoid any problems with heat, I found a great price on corrosion resistant .05" thick aluminum sheeting, $45 for a 36"x48" sheet. It will be far lighter as well. Good idea with the truck liner spray, hopefully it'll stick to the aluminum. Should reduce vibration and road noise too, plus protect it from salt spray and the like.

Thanks for the ideas!