I've got a PFS Intercooler setup (image below). And am in the midst of a doing a full rebuild. I bought this car several years ago with all this done.

As part of that, and looking into the mods that are already done and what I want/need to get done, I found some very old (like 2002-era) info on the PFS setup where there were numerous mentions of people doing "filter box mods". As-built, the PFS setup scavenges intake air from the intercooler duct. And, supposedly, at least at WOT the intake can be effectively starving the intercooler of sufficient cool air. So it was apparently common to seal off this connection and do a "filter box mod" so that the intake got air elsewhere.

But, being that the mentions were all from 20+ years ago, none of the old images remained. So I'm not 100% certain what was done. Separating the box and duct in a real clean way is easy enough. But what's the best way to mod the filter box to receive sufficient air? Holes in the bottom? Is any sort of ducting better?

Or is it as simple as just sealing the duct side and leaving the hole on the filter box side just open?

And a bonus question: Anyone know the purpose of the leftmost hose on the filter box below? It's just got a short-length of hose turned up at a right-angle that's capped off.

 

i dont know about all that.... the intake taking fresh air from the intercooler at a rate so fast that a significant amount of air doesnt pass through it reducing its effectiveness? highly doubt that is taking place. keep in mind the duct feeds the intercooler, battery and air box with outside air in stock configuration.

the real issue is the intercooler baking on top of the radiator while the fans are PUSHING all that hot air onto it. then on top of that i would assume you have a non vented hood? air flow in stock configuration or even in the set up you have there is what it is. without some seriously aggressive ducting, a vented hood or water injection, your air temp will always be "hot".

also going to assume you have those 2 cylinder type filters inside of that air box....

to maintain a less than "hot" air temp, you would need to be moving at highway speeds. flip that radiator around and keeping the engine bay cool becomes a simple task even with a non vented hood

the pipe with the yellow cap would have gone to the stock bov as a ricirc but you have the hks venting to atmosphere

the mod you are referring to would be done in your case by removing the coupler that attached the air box and the intercooler duct. you would then run some scat or something else from the air box to "outside". the open port on the duct would simply be capped. the intention is just to give everything its own air source and not to share.

 

Seemed a little unlikely to me as well. But, since I've got everything out from under the hood right now, it seemed as good an opportunity as any to improve things. It was actually while looking into better AST-mounting options that I stumbled on all the discussions about this filter box mod on PFS SMIC users.

Seems as good an excuse for an AD-9 hood as any...

It's actually got this massive double-barrel K&N filter. No identifier number anywhere on it. Ancient forum threads (again) claimed it was a "unique" K&N filter made just for PFS and that you could only get replacements via them. I'm going to try to clean it up as, given how difficult it was to access, I'm fairly certain it has never, ever been cleaned in its life.... which, I really have no idea about, but is likely 50,000+ miles. But, given the number of options K&N make, I'm also pretty sure I could found an alternative if needed.

Thanks. Seems obvious now.

 

A radiator or intercooler as a rule of thumb can flow 1/3rd of their surface area. Look at the ducting size and see how much "extra" air can come in.

Definitely don't try to draw air from under the car, that's dirty air your filter will have to work much much harder.

Nice period-correct parts, keep them as they are for all the style points

 

The PFS duct is pretty good quality and doesn’t vent the battery like OEM.

No good pictures but this is what I did…..

* I bought some plastic 1/4” screen and covered the hole inside the duct that leads to the airbox. Some clear silicone works great to keep the screen in place. Minimal restriction but much better at keeping butterflies and big insects off that K & N.

* On the bottom of the airbox and being careful not to compromise the strength too much, I used a hole saw in a couple different sizes in the area that corresponds to the gap beneath. That gap leads to the nose of the car and sources fresh air just like the “cheap bastard” mod on the stock box. I estimate the total area of those holes is equal to the opening from the duct, so it just about doubles air supply.
I also used that same 1/4 inch plastic screen to cover the holes from inside the airbox.

* Never liked the naked trailing edge of the duct tat goes against the IC. I went to the local U-Pull-it salvage yard and scavenged the rubber trunk seal from a BMW. After a bit of trimming I used it to seal the duct to the face of the PFS IC. The trunk seal has a spring metal core that secures it nicely to the edge of the duct. I think it actually looks factory.
* I deleted emissions and don’t run the air pump, so those unused ports on the back of the box are plugged by black rubber chair leg covers from the hardware store.

* I don’t really understand why that filter was ignored on you car. I can have the airbox out and on the bench in < 5 minutes. Clean and recharged and reinstalled in 30.
I pull the entire IC out in the spring and run a little degreaser or just dish soap and hot water thru it to clean. I think I get very respectable IATs for a SMIC and fairly quick heat soak recovery even in the Midwest summer. And, I think, probably less pressure drop than some other SMIC designs.

 

Great advice there @Sgtblue , thanks. I own an E46 M3 and I have some different weather stripping and seals as those are all starting to wear out on that car. I'll see if I've got something that'll work at-hand. The duct wasn't even secured to the face of IC on this car let alone sealed, so there had to be enormous leakage.

Where's your AST at? The line from the thermostat housing seems to go down and around the air pump... is it sitting behind the strut bar?

 

I don’t run a traditional AST. I think the mounting ear on the PFS is located with the stock triangular AST in mind. Mounting the round aftermarket metal AST would be awkward at best, imo, and going back to a stocker wasn’t going to happen. And any AST would’ve interfered a little with airflow. So it’s now deleted with a billet Banzai filler neck extension which very effectively performs the same function.
Billet Aluminum Filler Neck
The hose and nipple from the radiator was removed before tapping the hole and using an NPT plug. And plugging the radiator nipple. So that’s why you don’t see that hose. Never had any issues with bleeding air in the system. And I change coolant every other year.

 

Nice. I'll do that. It was actually a cooling issue (puking coolant on warm-up) that was my initial focus, but it's turned into a full rebuild/restoration now.

You can see in my first picture where my aftermarket AST was mounted. It was using the integrated mount on the IC. But it did leave the AST laying up against the face of the IC (can't have been good for airflow). Worse yet, to prevent metal-to-metal rubbing issues, they used some sort of thick rubber tape that melted over time, leaving a gooey mess on the face of the IC. It's not clogged up TOO much of it. But still some and it looks like ****. So gotta find a way to remove that without harming the fins.

 

It’s really a pretty good SMIC and intake combination IMO, and worth a little fussing. Bar and plate construction, about 2.5 to 3 time bigger than stock, with smooth cast piping and tapered tank, a good sturdy duct and the intake box was pretty easy to improve on. Plus the battery stayed where it was, which was important to me. My biggest criticism was that mount for that AST. But that turned out not to be all that big of a deal.

 

I had the setup years ago. It was shown that, under serious load/rpm, that the intake actually pulled air back through the IC. I did at one point cut a slot in the bottom of it and made a duct to draw air from alongside the radiator like an M2 intake, but as its relatively short it wasn't a huge hole. Maybe 1"x6". At some point I moved to a CWR intake and capped off the IC duct hole.

 

^ I’ve heard that but never seen the data/info. And mostly with regard to the stock intake/duct.
Can you point me toward a link or key search word? I would think/hope that’s possible only under VERY specific and brief load/rpm circumstances, and without modifying the intake box.
FWIW I do recall that AFTER opening the bottom of the box I had to adjust my manual BC just a bit against a small spike.

 

Semi-related, and not very important, so I'll just ask it here....

Anyone have any guesses on the boost loss from 2 open holes in the intercooler, each about 3mm in diameter?

The PFS SMIC has 2 holes drilled into the IC on each side of its face that were for securing a bracket on the duct to keep the duct firmly in place. I had just assumed the holes were very shallow and didn't actually go through the wall of the intercooler.

Turns out they do. And if you have bolts threaded into them it doesn't matter of course.

But this car didn't. So there were just gaping holes right into the sides of the IC. And for who knows how long.

Not a problem for me now. Everything's getting rebuilt. Just curious if it would have been an appreciable impact to its performance from before. I'm not particularly experienced with forced induction, but know that even tiny leaks found on couplers and the like can yield some pretty big power losses. So I would have to think that 2 open bolt holes would be noticeable.

 

It may have made some noise, even whistling, but I doubt you’ll notice any dramatic power gain after replacing those 10mm bolts. Maybe a bit quicker response since boost isn’t leaking and builds quicker.

Using short self-centering versions make them a little easier in the tight space.

 

Years ago I predicted this after doing some simple calculations. Back before I went single turbo. Then Mazda blew engines with the RZ model(I think) while track testing. All due to back hot air flow from the rear of the IC into the air intake.
Then they redesigned the air intake to not pull from the IC intake.
In-fact I beat Mazda to doing it myself by modifying the stock airbox inlet duct to pull air from over the top of the radiator.
Someone out there on the forum purchased it from me years ago,

 

You still have those simple calculations? And I’m assuming that was on the stock duct, stock IC and stock intake system…correct?