Write-Up: Building a Custom PVC Fenderwell Intake

Wait a sec, calculation on first page says L67 cfm requirement is like 725cfm?? Isn't that a bit high?

Nothing wrong with having too much CFM on a supercharged engine, as long as you can keep up with fueling demand. This means you'll need to tune the fuel map and/or add breathing mods at some point to compliment the extra boost.

Our engines typically suck between 450-500 CFM at full boost, 650 would be heavily modded.

That's what I was after. I thought typical cfm of 725 sounded high and if its more like 450-500 like you said, that sounds better.

I think I'll do my sealed naca 4" intake to my inline filter and then to the tb with a aem air bypass in between just to be safe. Now I just need to see if they make a 4" aem valve

I think another thing to consider is the filter's CFM rating doesn't count the intake plumbing, ducts, etc. Using a 725 CFM rated filter with 18" of tube, a bend or two, and the TB itself will lower the effective CFM to the blower down to probably the 500 range, which is acceptable. 450-500 CFM is the total amount of air moving through the engine, including all intake, internal, and exhaust restrictions. A 4" dia tube helps a little, but everything adds up, and the filter is the largest intake restriction by far, so makes sense to aim for a high number, imo.

llamalor2112 wrote:

I wonder, would a foam filter be more water resistant than my current cone?

From what i've read, oiled foam is the best. They're used on vehicles in desert racing and rally racing in the rain. More porous for better flow but are just as safe if not safer than knit filters.

Ive seen foam filters that let Nothing pass into the throttle body.Nothing. if you remove a KN filter you will see a coating of fine dust inside the throttle body,not so with a foam filter.if i ever get around to fabbing an isolated pressurized air box for the intake,ill most likely use a foam filter.I gotta say that at this point im K&N'd out.

I think each material has its advantage.

Paper (OEM, WIX) - best filtration, great flow when clean, but need to replace more frequently. Lowest cost.

Oiled Cotton (K&N) - good filtration, better flowing over time, long life. Needs maintained every 25-50k miles. Higher initial cost.

Foam (Oiled or Non)- better for high dust environments, needs cleaned and deteriorates over time. Typically less flow for size.

I'm a big proponent for the K&N, because it takes the advantages of paper filter design, and improves on it. Also K&N can last forever if maintained. I've not noticed dirt/dust getting through mine, but I don't live in the desert, either. My Riv breaths mostly humid Ohio country and city air.

Foam is popular for construction equipment, dirt bikes and tractors. It's not as high flowing, but you can get around that by using a larger one.

The reason a foam doesn't flow as well as an equal sized paper or cotton K&N is surface area. Paper and cotton filters use pleated accordion folds, so there's actually more filter surface in the same space than a flat foam surface of same size. You can go larger, but know that whatever size you choose, the pleated panel will flow more air. And if you've ever used any foam product for any period of time, you know foam tends to break down and crumble - it won't last forever.

If you want more flow, nothing beats clean paper, imo. If you want best off-road filtration, go with foam. If you want a filter with good flow that lasts the life of the car, K&N is it. Use a bigger (cone) version for even more flow.

AA wrote:

The reason a foam doesn't flow as well as an equal sized paper or cotton K&N is surface area. Paper and cotton filters use pleated accordion folds, so there's actually more filter surface in the same space than a flat foam surface of same size. You can go larger, but know that whatever size you choose, the pleated panel will flow more air. And if you've ever used any foam product for any period of time, you know foam tends to break down and crumble - it won't last forever.

If you want more flow, nothing beats clean paper, imo. If you want best off-road filtration, go with foam. If you want a filter with good flow that lasts the life of the car, K&N is it. Use a bigger (cone) version for even more flow.

Without a doubt, the foam is more porous than the knit K&N filters. Even if you compare surface areas, I think the density differences would make surface area differences negligible.

Only downside I see to the foam is the maintenance seems higher than the traditional paper/cotton filter.

I wouldn't assume foam is less restrictive, just because it appears more porous. Remember, it's like 100x thicker than paper (which is really more a woven cloth) and again foam has less surface area. I bookmarked a good article on chainsaw air filters, which really explains a lot of the differences. For chainsaws, the objective is to filter sawdust, pure off-road use. Foam works best. They make the filter extra large to make up for the restriction. The link gives a lot of the bonuses for foam, but also reveals the disadvantages, and explains why paper and cotton (gauze) are mostly supplied for OEM:

Link: http://www.maxflowfilters.com/Foam%20Vs.%20Pleated.htm

"Oiled foam does a tremendous job of filtering. The thousands of small pores offer tacky spots throughout the depth of the filter to trap even the smallest particles. As the airflow twists through the pores it is cleaned and this has the advantage of having immediate high filter efficiency, even on a freshly installed filter. The disadvantage of this twisted airflow path is that there is some additional restriction, however, the Max-Flow filter uses a larger area foam filter element and a larger cover so the CFM of our foam filter is equal or better that of a new gauze or polyethylene filter."

"Gauze and paper have a high CFM airflow when new, foam will have a lower CFM for a given surface area, so typically they are made slightly larger to off set this. Typical off road filter application should have 2 times the surface area, but chainsaws live in a much harsher environment and need higher."

What this says to me is even the supporters of foam filters know they can't compete with pleated paper or cotton K&N with regard to CFM, so they make their filters larger for added flow.

Another concerning fact about oiled foam is that once the oil wears off, if you don't re-oil it then MORE dirt passes through. If you let a K&N go too long, it keeps filtering but the amount of flow might drop - not very much if using a large cone, though. I clean mine about once per year, and the MAF doesn't drop much if at all when dirty.

"Since it is the oil in the foam, rather than the filter foam itself is not doing the filtering, at some point the oil in the foam will be used up. At this time the foam filter must be cleaned or the dirt will pass through the foam and into the engine."

Here's a neat calculator for flow and power losses using different filter materials. Not for supercharged, but I'm not looking at exact numbers, just for relative comparison.

http://www.secondstrike.com/Technical/AirCleanerCalc.asp

I used 300 peak HP, RPM 5300, 231 CID, high perf/track engine type, specs for K&N E-1009 cylinder.

Results E-1009 (max HP loss):

Paper: 0.36 HP
Oiled Cotton: 0.12 HP
Foam: 0.87 HP

Very low loss prediction, but foam is 7x more restrictive than K&N.

Using same power and engine specs, here's the same calculation for stock size panel:

Results OEM (max HP loss):

Paper: 0.51 HP
Oiled Cotton: 0.17 HP
Foam: 1.23 HP

Since these loss predictions are meant for N/A engines, we can they would be magnified if supercharged.

Ok I saw this somewhere but I can't find it again, where can I get some piping or tube to go to my intake instead of the stock one

Home Depot/Lowes. Get the 4" corrugated non perforated tubing. 10'/$5

bmcd9179 wrote:

Ok I saw this somewhere but I can't find it again, where can I get some piping or tube to go to my intake instead of the stock one

You can go to Home Depot, Lowes, etc. and get some ABS or PVC pipe or you can buy aluminum or plastic tubing online.  Search around a bit and you should be able to find a few suppliers.

Personally I think PVC or metal is the best way to go. I kind of regret not doing PVC, but the flexible tubing makes removal super easy.

Agreed, im not a huge fan of the corrugated stuff, very restrictive

It's not that it's restrictive, it's just harder to make it look nice.

I still think the flex tube doesn't look bad to my eyes. And this isn't a competitive racing application so the amount of restriction we're talking is irrelevant for most of us. I like the tube intakes as long as they're done with smooth integral bends. when I start seeing several elbows and clamps it's a turnoff. No flaming! haha just an 'imo' post   

I was just browsing around Lowes and I found some aluminum flexible tubing. I think it might be for dryers but I'm not totally sure. I just saw "4" Aluminum Tubing 8' Section" and snagged it. It seems to be easier to work with than the corrugated tubing and less restrictive. Just waiting on the silicone couplers to get in now and I'll have at it. I'm also going to make it go into the fender this time.

Anyone have a suggestion as to where to place the sensor? Mine has just been dangling inside the tubing ever since I made this setup and I want something not as ghetto. I suppose I could try drilling into the tubing but I'm not sure if I could get a good seal.

I've used that stuff for dryers before. It's kind of flimsy, so be sure to secure it well. I don't know how durable it will be, but it should tolerate heat at least. Inspect for rips and holes periodically. Install the IAT sensor in the air stream, just after the filter. May need to get creative mounting it with this type of flex hose. Seal with RTV.

There are two different types of 4" dryer vent - there's the floppy stuff you find pretty cheap, then there is a much more rigid design you have to use if you have a gas dryer. Still flexible, but a lot stiffer. I would guess that stuff could handle being used as an intake duct without collapsing. Stay away from the floppy stuff though.

deekster_caddy wrote:

There are two different types of 4" dryer vent - there's the floppy stuff you find pretty cheap, then there is a much more rigid design you have to use if you have a gas dryer. Still flexible, but a lot stiffer. I would guess that stuff could handle being used as an intake duct without collapsing. Stay away from the floppy stuff though.

It's rigid enough to hold itself fully extended vertically, but horizontally it will sag (8ft long). Not sure if that tells you anything or not.

That sounds like the more rigid stuff I'm talking about. I'm not a big fan, it can puncture easily (thin aluminum) but it is great for temporary or mockup use.

Old thread, quick question. Do I need to tune if I want to put in a FWI?