DIY Airbox

[Edophus]

Hi guys, as i'm pretty clueless i need some advice on this, when i come to do my itb's i'm going to have to build an airbox around them but due to the limited space i wont be able to use an off the shelf airbox, so i'll have to make one.

I'm looking for any ideas on how to go about it, and what materials are best to use, and also is there any general rules of thumb on how big to make it?

Any advice would be great.

[RST]

For a DIY option I'd go for GRP.

You need to make sure the capacity is around the displacement of the engine for a start according to the rule's of thumb I've found.

I'd get hold of some EPS (Expanded Poly Styrene) or some of that blue or red foam you see on building sites (take a look around your place -LoL). and I'd hack away with a bread knife, hacksaw etc then finish off with sand paper etc. If there's any sharp edges or ridges / profiles you want, try a modelling store for something easily cut like balsa wood.

Then I'd cover the lot in brown shiny parcel tape. You should then be able to put a a good few layers of GRP -stuff like chopped strand matt and the normal resin you can get from car factors.

Now you can go one of 2 ways -make your box directly by moulding onto the EPS former. Or you can make the former and make sure you put plenty more GRP layers on. With the latter option, you are going to make your air box moulding off the one you just did so it needs to be really strong.

It should pop put OK and you can trim of the edges before you remove it essentially while the GRP is "green" before it's fully cured with a stanley knife. If you then leave it for a week to fully cure you can then carefully sand everything back to make your mould. Not too sure about release agents but I've used PVA adhesive before but you can buy specific stuff. For something like this a gel coat gives a nice finish but can't really see the benefit personally. Get the mould you just made (all nice and smooth / polished) and put your release agent on. Then you can brush the lot with resin and start laying up the chopped strand mat. Actually better stuff to use is called rovings which is a woven sheet of fibre like you see in the CF parts rather than chopped mat but it's a bit tricker to use. Once you've got 2-3 even layers on leave it to set. Again, trim off the edges after a few hours while it's still green. Then leave it for a day before you remove it from the mould. This way, you'll have a nice smooth surface on the exterior (the interior will be rougher though so make up your mind beforehand which way works best for you).

...I might not have explained this very well but I've done it before and it's easier than you think -but it is messy.

I'm thinking of exactly this myself and can get bulk GRP and other materials from the likes of Dingbro so if you wan't to give it a go I can help you source materials.

[Edophus]

Thanks that sounds like a good plan, i'm up for getting some of this foam and giving is a go

[Roman]

A method that I've heard, as used by some pros that work with carbon fibre etc...

Is to shape something out of polystyrene, and then carbon fibre/fibreglass/whatever straight over the top.

Then you pour in some type of alcohol (cant remember what) and then all of the polystyrene dissolves, leaving you a nice hollow airbox or whatever without having to mould it into two parts or whatever.

The same principal is used in bronze sculptures etc with wax, to make the inside of moulds or something etc I think. ('lost wax' techinique)

Not that I make bronze sculptures in my spare time or anything. *cough*

[RST]

You could pour in something like acetone (nail varnish remover) or MEK. But it's very messy and will give off very toxic fumes with EPS.

Lost wax technique they make the prototype in wax, bury it in casting sand then bake the lot so the sand sets hard and the wax runs out leaving the cavity for casting the metal.

[canadam]

Originally Posted by Roman

Then you pour in some type of alcohol (cant remember what) and then all of the polystyrene dissolves, leaving you a nice hollow airbox or whatever without having to mould it into two parts or whatever.

Acetone, likely. Most nail polish removers would work.

EDIT: I should read all of the posts before I decide to make one

[MANDALAY]

All my custom work with stereos, l never use GRP especially in a car where it gets very hot and especially in an engine bay.
Look a DOWS Vinyl ester . Works like GRP BUT has a much higher temperature rating that will not warp.
Its much dearer but do it once and do it right.
ps FI cars.

[RST]

Seems like there's a whole heap of stuff that can be used if you look round at ready made ones. GRP's a generic term, though I'd agree, look for a resin with characteristics for what you want to do. Is that an epoxy resin MANDALAY (looks like it on a couple of web pages)? I have a very small tub of epoxy laminating resin -but nowhere near enough to do an air box.

...I'm still waiting for the guys to drop off that foam Edophus -sorry I've been away on business this week, just chased them up again now.

Richard

[MANDALAY]

Yes its an epoxy vinyl ester, which can take a lot of heat.
Some versions right up to 250 degrees celcius.
You can laminate thin and it will not warp.
It gells up slowly with a lower exotherm.
Most polyesters even with hot water will warp.
None of my car trim parts that l made have even moved after 11 years.
PS imo l would be puting something over the polystyrene before you start to laminate.
l thinly brushed on a laminating clay which set then l used a PVA mould release not wax.
You might find that GRP attacks the polystyrene.

[RST]

Then I'd cover the lot in brown shiny parcel tape.

(whatever resin used)

PS imo l would be puting something over the polystyrene before you start to laminate.
l thinly brushed on a laminating clay which set then l used a PVA mould release not wax.
You might find that GRP attacks the polystyrene.

...I thought you might get away with a std. polyester resin on a mould that size, but must admit, I'd build it up quite thick so it didn't warp.

For a DIY job -do you think you'd get away with spraying a few layers of thinned down PVA adhesive as a release agent? I've done the odd very small bits and pieces using brushed PVA adhesive and it worked reasonably well.

I had about 25sqm of rovings untill about a year ago -new I should have held on to it just in case. LoL.