Collecting Parts For CAI/ Building Heat Shield

[longms]

I am collecting all of the parts for a CAI and building my own heat shield with metal sheet, heat wrap and some rubber plumbing insulator for seals around openings. I am trying to figure out the right size filter to get and am not sure if I should try to fit the biggest one I can in the box or if there is a certain size that might be optimal. I was looking at conical ones that are 3" inlet and have 5-6" bases and have 4-5" ends and are about 5-6" in length. The cylindrical ones are 3" inlets and 4.5-5" diameter and 5-6" in length. Also are there any filters that are better than the others? I am looking at K&N filters but am trying to save a few bucks if there is any brand other than the listed that will work just as well.

I will take pictures once I get all the pieces together and start "engineering" my new cold air intake system. I know there are heat shields for sale but do not feel like spending $100 on a piece of metal with rubber seals on it. I think I will try my luck with building one

[longms]

Admin---- can someone move this into the general topics??? Thanks

I dont think a double post is the right way to go about it

[nando]

air filters are all about surface area. you want to get the biggest filter you can fit in the space you have. I think I crammed a 9" long x 6" diameter (tapered to 5") K&N, but I don't have an AFM, so yours will have to be shorter.

I was measuring about 10kpa of vacuum at full throttle with the stock airbox/paper filter. that went down to about 2kpa of vacuum with the K&N, it was almost as good as an open throttle (which still pulls vacuum at full throttle, but that's another story).

there are always 3 mistakes I see on E30 "cold air intakes"

1) tiny filter - maybe 3" long, 4" diameter. Probably half the surface area of stock.
2) no shield. you're sucking 200 degree air out of the radiator. that sucks ;)
3) bashed up/dirty filter. you aren't getting performance from a filter that looks like it was found on a sunken U-boat. clean the damn thing or go back to stock.

these three are probably why the meme exists that you can't get anything out of an intake. This isn't true, although any gains will be small if your engine is stock, and non existant (or negative) if you're intake looks like any of the points above (usually all three in E30 circles).

at the E30 picnic I think I saw two 24v swap cars with proper shields. The rest had tiny, grungy, bashed up filters sucking hot air right out of the radiator. granted I didn't have a shield yet either. I don't know how much that was costing me, but I still gained 10whp on a dyno.

[longms]

Thanks a ton. I don't think that I would be putting a K&N in until I either bought or made a heatshield for the filter. If not then I would only be after cosmetics and the sound. I guess I will have to get the shield mocked up first before I order a filter so I can see exactly what I can get in there.