Subaru Impreza GC8 & RS Forum & Community banner
1 - 20 of 63 Posts

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #1 · (Edited)
My custom CAI using 3" pipe and the stock airbox

Well here's my attempt at the best of both worlds...keeping the stock airbox and having the flow of a 3" intake tube.

..finished install




some pics along the way....



after test fitting I marked the tube for position...


all glued up....






...all wrapped with aluminum tape and ready to install. The tape helps with radiant heat. It's good for lowering temps by about 15-20º



OK, why I did this. More than anything because it's fun to tinker :)

I also wanted to retain the stock airbox as well as the flat style filter. I honestly don't like the idea of a filter in the fender because it's harder to service.

I did learn a few things: I didn't really feel any noticeable jump in power during the test run with this set-up which I expected, but something happened I didn't expect. The intake is much quieter now than it was with the PDM intake and stock airbox. Go figure. I also didn't expect it to fit better in the car with a larger tube, but it does because I was able to set the position of the elbow where I wanted.

Now even though I knew gains would be negligible I also plan on cams and a reflash. I already have a free flowing exhaust so it may net some gain after all is said and done. We'll see.

I also learned regular JB Weld doesn't seal voids very well ;) but JB Kwik Weld does as it sets faster, but it sets too fast for the whole job.

Anyway the mod is pretty straight forward. Just requires some hacking on the airbox ...OK alot of hacking :D. Since I bought the PDM intake years ago it was fairly inexpensive too. I got the 3" elbow and coupling off ebay for around $30 shipped and after that I just needed epoxy. Now for most of the grinding I used a die-grinder with a rotory file, but a dremel would work too. I also took out all those fins or whatever just for good measure. All in all I think it came out pretty good. All that's left now is to insulate the elbow like the rest of the intake. :)
 

·
Registered
Evo X GSR, 07 Civic Si
Joined
·
679 Posts
hmm living in CA it would really help if i cut up my stock airbox and cover up the 3'' cold air intake arm in the engine bay. it would make the car look completely stock to the bones :D

some of the Evo guys in California did this mod. and the lower intake box temperature idea is pretty sweet.
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #3 ·
update:
Drove the car a bit more today and learned something new. When intake temps are cool the car has much more bite and it is breathing much better on the top end. I can actual feel a difference. However I also noticed that when I get hard on the throttle the intake air temps increase quite a bit according to my Scanguage II. This tells me that hot air is being sucked into the intake from the hot engine bay. I can't believe the difference in power depending on IAT. It's quite dramatic. I knew this was an issue before, but now it's even more apparent so what to do. Cut some kind of vent or NACA duct into the bumper or take out a foglight..hmmmm....I'm not sure yet have to give it some thought.
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #4 · (Edited)
OK I couldn't leave it alone so here's where I'm at:

I went ahead and insulated the elbow...


I removed the right fog and ran a duct to the hole...




I blame this whole thread on the Scanguage 2. Before I bought it I was blissfully ignorant of the high IAT's. :curse: :D

Update
Well's here's where I'm at now. I pulled off the insulation on the piping because the temp difference is minimal, but left it on the airbox. In an effort to further lower IAT's I'm planning on installing a WRX/STI hood with a K&S scoop delete to vent hot air.

 

·
Registered
95 GC 371hp/355tq ej25 1.5xtr
Joined
·
4,494 Posts
dude thats awesome, im just curious, what was your IAT before and after. i have a homemade ganzflow, IM/TB spacer and im still around 90-100 degress.
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #7 ·
Thanks :D

OK I actually just got back from doing some tests. I kinda ran a small circuit with different intake configs. Half stop and go at lower speeds and a 5 minute or so run at 60MPH.

Now the temps were only slightly lower ( about 5-7º) running the duct to the foglight opening as opposed to just having the CAI protrude into the fender well. I also noticed that throttle response suffered slightly. Probably too many bends with that duct. So I removed it.

OK I did 4 runs:

1st run) I pulled off the CAI and let the air flow directly into the elbow. I recorded 100-109º during the course of the run. Throttle response was good though.

2nd run) CAI reinstalled, but I left the fog cover off so I had a nice big hole to let air in. 91º steady during most of the run.

3rd run) reinstalled foglight and cover with the CAI and interestingly the temp was about 92º during the run. I was surprised about that. I figured closing up the hole would have more of an effect.

4th run) this was sort of a control run so I again ran with just the elbow and again the temps were around the same. 107-109º

ambient temps were 75-72º during my runs.

I think the airbox gets heatsoak when sitting too so it takes a bit for temps to drop also sometimes. Aside from that the CAI is doing it's job. I do wish I could get closer to ambient temps. I think having a WRX hood with a vent would cool things down even more though giving the heat a place to escape to.

After all that I decided to run with the CAI of course and the fogs installed. The roads here are too dark at night honestly.
 

·
Registered
MY99 OBS
Joined
·
1,690 Posts
uh are you gonna put some mesh wiring over the pipe opening to prevent rocks, etc from getting sucked in? Looks good, i was thinking of doing something similar to this. Stock box, custom piping into fender, custom piping leading to somewhere into the front bumper so air is forced in while driving. i have been trying to think of a way to have a switch to cut off the air coming in from the front and having it just suck air from inside the fender when its raining or something. Has anyone done anything like this?
 

·
Registered
MY99 OBS
Joined
·
1,690 Posts
what was the temperature outside? dang i guess pulling air from the fender is good enough. What about the setup that uses the stock air box that is connect to the fender and uses a cone shaped filter. Insulate the piping from stock box to throttle body. But i guess you would then lose low end torque? :lol: what to do?!
 

·
Registered
95 GC 371hp/355tq ej25 1.5xtr
Joined
·
4,494 Posts
you have the plastic IM. you bastard...lol. thats another reason why you will see more gains from it than people with the metal one. i have IM/TB spacers and i can still feel my IM getting hot on some days.
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #11 ·
you have the plastic IM. you bastard...lol.
he he....;)

Yea that composite IM is advantageous. I actually have a small leak on the right side IM gasket I haven't fixed yet. When I do I plan on wrapping it as well.

I'd like to use gold foil as it blocks 78% of radiant heat plus it would look like something built by JPL...:D

all I'd need then is a decal that said "POWERED BY NASA"... :)
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #14 ·
The intake pipe is from PDM Racing and the rest of the material came from ebay. I'd like to add that since PDM stopped making the intake pipe something else would would have to be fabbed out from the elbow, but that shouldn't be a too difficult considering the availability of different degree pipe elbows and silicone elbows. Neoprene hose would work too.
 

·
Registered
99 OBS
Joined
·
276 Posts
The intake pipe is from PDM Racing and the rest of the material came from ebay. I'd like to add that since PDM stopped making the intake pipe something else would would have to be fabbed out from the elbow, but that shouldn't be a too difficult considering the availability of different degree pipe elbows and silicone elbows. Neoprene hose would work too.
ok thanks, do you know what degree that first pipe coming from the airbox is? Having a hard time finding that pipe, is it 45 degree, or like a 75 degree pipe? Wonder if i could find it at home depot, ebay isn't coming up with much for that pipe.
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #16 ·
OK basically I have a 90º aluminum elbow grafted into the box. The other pipe is the intake from PDM. It has about a 50º bend in it.

OK here's what you can do. Go to ebay motors and type "3" aluminum pipe" in the search window. This will come up with all kinds of pipe. 90's and 45's mainly.

So what you can do is use a 90 as I did in the airbox then use a 45 with long legs. What you do then is cut the legs down until the pipe fits how you want. You may also need to cut down the 90 as well and if so cut it before gluing it to the airbox. Do all your test fitting first before any gluing or cutting OK. So basically you'll end up with the 90 coupled to the 45 going into the fender.

Another option is to just use some neoprene hose coming off the 90. This isn't as pretty though lol.

Good Luck :)
 

·
Registered
2005 2.5RS Black
Joined
·
48 Posts
whats the advantage of keeping stock airbox??? cuz i have seen some with the pipe directly into the engine and no airbox... why is this?
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #18 ·
Keeping the airbox or torquebox as it's often referred to gives the throttle body an immediate reservoir of air. This increases throttle response and torque. Though I'm not exactly clear how it helps torque, but it does.
 

·
Registered
2005 2.5RS Black
Joined
·
48 Posts
Keeping the airbox or torquebox as it's often referred to gives the throttle body an immediate reservoir of air. This increases throttle response and torque. Though I'm not exactly clear how it helps torque, but it does.
hmmmm:_sure: im skeptical...
 

·
Banned
'04 RS PBP w/ Black Tarmacs
Joined
·
1,805 Posts
Discussion Starter · #20 ·
...about the TR or Torque?

I know the physics behind the TR. I take that as truth. Even the WRC car's have a similar setup. They step up to a much larger diameter IC pipe just before the TB.

From what I've read the torque factor I believe to be true as well, but I'm just not sure of the physics behind it.
 
1 - 20 of 63 Posts
Top