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I hate the stock airbox, so - 2.4i intake

10K views 38 replies 11 participants last post by  erikkress1320 
#1 · (Edited)
Updates at end of thread.

I've had to venture below the airbox a few times now in my S40 2.4i. Now I may be clumsy, but every single time this blasted thing has been the hardest part of the repair by miles.

Most recently I was heading under there to take a look at a sticky starter (which seems to have solved itself for now). I did what avenger09123 suggested - cut off the leftmost "arm" holding the box, which was a hugely helpful maneuver, I was able (just) to remove the box without shifting the engine.

Though I got the box out, I severed a coolant hose doing so (my fault), and was generally fed up with its bulk and how tricky you had to be with it and everything around it to coax it out.

Enough was enough for me, so in the interests of serviceability and not noise, MPG, power, or any other dubious claims that come with an intake:



This is a Spectre 9833 inline air box with two silicone elbows (trimmed a little), a Spectre 87051 MAF mount which seems to have our stock MAF tube's inner diameter (simpler than the similar Spectre 9405 kit), and a bookshelf bracket holding the ECU (subject to improvement, hopefully). Other things include a 3" coupler and a 10mm breather filter, which clamps around the breather line with the OEM 90 degree elbow removed from it. Also: sink strainer mesh before the MAF tube to emulate the pre-MAF mesh in the OEM box. It's a good hint from a member on here, from the Cheap Mods thread I believe. I had a lumpy idle and hesitant acceleration before doing that, silky smooth now.

Notable things:
Oiled gauze air filters are notoriously less than ideal. I'm using foam as a pre-filter (oiled lightly with foam-specific stuff) to hopefully shore up the filtration a bit on both the airbox filter and the breather filter. You can see it on the breather filter, I did something very similar with the one inside the airbox.

It's quiet until 4k RPM! This is why I chose the relatively small diameter airbox - didn't want any din from an oversized one. Ironically in my case it's quieter than the stock setup at low RPM, as the "elbow" going to the snorkel was rattly in my S40. Per Spectre, the CFM rating (of the box, not just the filter itself) should be well over what's needed for the 2.4i, and I'm certain I haven't lost any appreciable amount of power.

Figured I'd share an inexpensive way to throw together a very simple intake for the 2.4i. No codes so far, but I'll update with developments if there are any.
 
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#3 ·
I never had an S40 with the early airbox resonator, so I can't say I've ever had trouble with oil changes. I did have a lower engine cover with the hole in the wrong spot though, had to hack away my own oil drain hole - that was fun

I can finally get to the transmission fluid dipstick without taking off the ECU cover to make enough space for my hands - that's an upgrade for sure
 
#4 ·
Sure Seems - these - 2.4 with Natural Breathing - would Benefit - Most from Lower Intake Porting & Cams . .
Matching that Upper Better to Lower "Ported Unit" seems would be 15HP .. then Cams 10HP so Combined 28HP . .
Sure would be Rev Happy . .

Pop lower unit on E-bay for $50. and Ship it to Me ~ I'll Port it for $325.00 it's really easy - "DIY" Bolt On

ps: Have to take a Look at Exhaust Manifold ~ Make it into Header ..
 
#6 ·
If anyone spent that much money on a 2.4i i think id, actually i spent about that much on my old 2.4i in odd-ball accessories so i guess its not that crazy lol
 
#5 · (Edited)
That is awesome dude. I never considered in an IN-LINE air filter, that's awesome.

That filter is fine, the 2.4i only pulls 165 CFM at 6500RPM if you account for stroke, RPM, and volumetric efficiency, so you'll be fine on a filter that size.
 
#8 ·
Yeah, and I'm hoping foam doesn't restrict it too much - I really don't trust the bare filter on its own. I have 1/4" 30PPI stuff on there which I suspect won't be enough, so I may bump it to 60PPI later on. Planning on doing a UOA on the setup as is and seeing what comes up.

Photo was being weird on some browsers, I think I fixed that
 
#7 · (Edited)
Porting Increases volumetric efficiency

Turbo's are getting 11-12Hp to say 14Hp on Lower Unit Depending on Tune ~ that a Motor that's Being Assisted Via ~ Turbo .. volumetric efficiency .. is way Lower on on Vac Pump ~ Normal Motor ..
Any Improvement in Going to achieve Higher Results , seeing 2.4i already has Header style Exhaust - Now the Front of the Motor needs to be Un_Corked ..
Matching the Upper & Lower Unit and Ported Lower Unit ~ 15Hp..

( 2400cc / 2 ) x 6000rpm/1728 = CFM 254.254

Then Take Cu. Ft. Min. 254.254 x .85 volumetric efficiency = 216 C. F. M

216 CMF could be Bumped Up to .92 or More with Porting 234 CFM through Motor ..so approx 3.75 Cu. ft. Per Cly. ( Increase )

ps: Exhaust Header - Looks pretty good - I'd maybe do Port Match to the Gasket as on Turbo Motors the Exhaust Flange is under sized .080 & Shifted .060 . .
Most Likely the ~ 2.4i Exhaust Ports in Head aren't Aligned any Better to Manifold Exit ~
 
#9 ·
PORTING WOULD Bring may more then Cold Air ~

( 2400cc / 2 ) x 6000rpm/1728 = CFM 254.254

Then Take Cu. Ft. Min. 254.254 x .85 volumetric efficiency = 216 C. F. M

216 CMF could be Bumped Up to .92 or More with Porting 234 CFM through Motor ..so approx 3.75 Cu. ft. Per Cly. ( Increase )

ps: Exhaust Header - Looks pretty good - I'd maybe do Port Match to the Gasket as on Turbo Motors the Exhaust Flange is under sized .080 & Shifted .060 . .
Most Likely the ~ 2.4i Exhaust Ports in Head aren't Aligned any Better to Manifold Exit ~
 
#11 ·
#13 · (Edited)
2.4I is pretty Good seeing it has 4 Valve Head and Medium Header with 11:1 Compression ,so more Like .88
But there are Improvements to be Had , as Described . .

I went back through the Calu. using more Acute Numbers : 228 Cfm @ 6000 Rpms
Ported would be Up around 242 Cfm ..

Author of Formula _ says Turbo Motors today are 100% or More as to Recovery of Waster Energy being used to Pressurize Intake .. I don't see it this Way has As the Turbo's are Very Restrictive
Hence Cutting Back of the Exducer Wheel and Opening up Waste Gate some ~ allow ~ a Lot more Top End - Higher Spin on Turbo also .. - When I Port the Turbo Manifold I also Open up - Internal Passage way to Main Exhaust Scroll


Porting the Lower Unit and Matching the Exhaust Manifold Plate ( S. Steel ) probably SS409 as those do get Rusty ~ Port & Ceramic Coat on that would be 1 step ..
Better step would be Matching Up and Streamline Lower Intake Manifold - Taking out all the Casting Web , Major Roughness . . Steps between the Mating Surfaces - has to be at Least 16Hp / 12 ft. lbs Tq. in there .. Dan
 
#14 · (Edited)
Some interesting points:

Per the Amazon customer Q&A page, the filter box can be oriented both ways, with the cone facing incoming air, or facing the throttle body. There is some CFM benefit to the latter, and that's how I originally installed it (by mistake).
I've since flipped the box so the filter cone points towards incoming air (the prefilter was wrapped around the cone, so for now that's really the only valid orientation from a filtration standpoint).

Throttle response is a bit more similar to stock than with the filter reversed (less jumpy)
Induction "honk" can be heard sooner than with the filter reversed. It's not loud to start, just a tone difference. Now starts at ~3k, as opposed to ~4k with the filter reversed.
I may wrap the prefilter on the inside of the cone and reinstall it reversed just so it's quieter in the future, but I'm keeping it as is for now.
 
#15 ·
What No Electric Fan to Boost Air Flow ?

What CFM is rated for ?

How many Sq. Inches of Air Filter ?

Anyone running 70mm Throttle-body ?

Aren't there any other wireless throttle bodies ? sure seems someone would have come up with Nice set up
by now , seems VW 2.5 5 cly. has more support . .
 
#16 ·
365 CFM forward, 427 reversed per the guy from Spectre one of the buyers spoke to.

Can't imagine that the throttle body is a bottleneck for the 2.4i (don't think the Porsche one bolts up) nor is the stock intake.

I have a 2.5 Golf, and would spend probably $2k+ to get an appreciable horsepower gain - intake, intake manifold, exhaust, tune. Even so, it might only make the 200 mark. Lots of noise, still not much power. At that point why not buy a t5?
 
#19 · (Edited)
Somewhat related update:

I've had super low idle LTFT values related to: https://forums.swedespeed.com/showthread.php?401201 , https://forums.swedespeed.com/showt...-Grumbly-quot-until-warm-then-runs-great-2-4i

As I had disconnected the crankcase breather from the airbox and it now has its own filter, I had a bit of flexibility to mess around with the left over vacuum line "elbow". Usually the vacuum ejector valve only is sold in a full assembly (~$100), but P/N 30744402 (can be found under $30) is used on both turbo and N/A 5 cylinder P2s. Remarkably similar to the original, but with "ribbed" nibs on the ends. With some hose trickery and home depot clamps it can be made to fit:

Idle LTFT has gone from -17% to just around -2%.
 
#20 · (Edited)
Update on ECU bracket:

I drilled out and bent a "safety plate" I had bought for like $2 from Home Depot a while ago with the intent to replace my jerry-rigged bookshelf bracket ECU holder. This gave me a few more placement options, and much better appearance once painted with hi-temp grill paint.

That coolant hose that wraps around the ECU on my car limits how far towards the radiator I can move the ECU. I was able to swing it to the other side of the ECU, by relocating one of the hose "holders" by the radiator. Gives about 1" clearance with the ECU.

I attempted installing the ECU the other way around, with the heatsink facing the radiator, and found that the wiring bundle had to be quite strained to achieve this placement. I decided to just angle it upwards to hopefully improve heat dissipation but ultimately opted not to flip it around. The wires of the bundle aren't actually "bundled" in all places, and their insulation is aged and stiff.

 
#21 · (Edited)
Looking at doing this here hopefully next week. I know you mentioned you had issues a while back with the grumbly idle until warm. I recently replaced that whole vacuum hose with the brake ejector valve and what not. Did doing this intake cause your issues with the hose, or was it just aged?

I just want to make sure doing this won’t cause the hose to prematurely fail, I doubt it would but wanted to check. Any updates after running this for a while? Any issues with cooling the ECU? Or any issues with anything else? Thanks again for the info on this, looking forward to doing this (I hate working with the stock air box anytime I have to do anything to the car).

Edit: also another question. I’m looking to make the air intake bring in fresh air from directly in front of the throttle body and through the grill. If I had a pipe come straight into the throttle body with no right angle, would this throw a code on the MAF? I’ve heard the MAF on this motor is super sensitive to high volumes of air coming in without being slowed down first, but may just need some trial and error.


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#22 ·
The vacuum hose had gone south well prior to the intake being installed, so they're completely unrelated. If you have a new one, you're good to go.

No issues with anything thus far. I would consider doing what I did by wrapping the cone filter with a layer of oiled foam. I have used those filters naked before and there was dust on the wrong side of the intake. That dust makes its way into the engine, scores the cylinder walls and eventually loses you compression. Next oil change I'll be running another used oil analysis to know for sure what effect this filter setup had on silica in oil - that'll be a scientific answer to whether it's safe or not.
Either way you'll have more air filter upkeep to do here, as you're replacing the stock air filter with an objectively inferior set of filters that let more dirt by.
Cooling seems okay so far, but be advised that placement of the ECU is finicky, in that it likes to bang into the fan shroud or interfere with the shift linkage. Special care is required with the wires, which get stiff and brittle with age. You'll have to spend some time mounting it. No heat issues yet, but I've only driven in up to 90 degree weather or so.

I wouldn't go the straight through the grill route for a few reasons. I know that intake design is used on the PCP concept and seems cool, but you're on the money - the MAF knows what it likes. Somewhere up there I mentioned that the car idled kind of funny until I added mesh ahead of the MAF, and that was with similar-to-stock routing. I'm certain the MAF would be harder to make amends with if you go straight out with the intake, and even if the car runs okay it may run rich all the time.

Additionally, the routing I went with here retains some resistance to water/dirt intrusion due to the bends, whereas with the straight out design the filter media is getting hammered with whatever is in front of your car, with no bends to slow it down first. The filter will go bad faster this way too.
 
#23 ·
Additionally, I highly recommend a rain sock if you're operating a cone. I have moved away from oiled filters due to their need to be cleaned and re-oiled and drained of excess. Basically I wanted to remove my own potential for error and destroy parts (particularly the MAF). I went with a dry AEM filter. To supplement this to avoid rain soaked Colorado days, I went with a rain sock from Outerwears - supposedly their design of the mesh makes it inherently hydrophobic, whereas everyone else I could find was a coating that had a 2 year lifespan before you had to buy another. So now on dry days it acts like a pre-filter. On wet days I don't have to worry about poor drainage in the construction areas of I-25.
 
#31 ·
After-summer update: no ECU heat issues to report, driven in 90-100 degree weather a couple times. Have barely driven during lockdown, so haven't had a chance to do a UOA yet.
Despite oiled filter and "prefilter", no MAF issues to report. Didn't drench them in oil, though. Used the tacky Maxima stuff.
 
#32 · (Edited)
Update: the cheapo maf adapter cracked and no longer sat flush with the tube, with a visible air gap. Also found a pebble (!) on the wrong side of the air filter. Silicone elbow past the airbox had brown water stains in it, throttle body had fine white powder in it. No one seems to make a suitable air filter for this air box, so I'm scrapping this system for now. Sent off oil for a UOA to verify just how much junk made it into the engine, but even if that miraculously comes back clean, not comfortable keeping this on.
 
#33 · (Edited)
I have an elbow with the MAF bung from this CAI available: CCI Intake System, Volvo S40/V50, C30 non-turbo it would help. I also have the little filter thing. I had pulled the CAI system off a 2.4i S40 and converted it for my T5. These were leftover parts.
Automotive exhaust Musical instrument Door Material property Composite material
 
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#35 · (Edited)
Got the UOA back. Si at 6ppm, just like with the stock airbox.
I'm frankly not sure how that's possible with visible dirt smears and dust past the filter, but that's a very good sign.

Put in the below arrangement temporarily (could go with an AEM dryflow since not in-line airbox anymore), drove it once and ripped it off, and spent 2 hours going back to OEM. The open element was just embarrassingly loud.

Judging by that UOA though I can probably continue to run my in-line setup... will see. I've found that I don't like the faff of oiled filters, and that airbox has just the one compatible filter - one which others have had trouble with, too.
 
#36 · (Edited)
Still rolling around with the stock box. I reinstalled it without the pre-MAF mesh (lost it while it was in storage), and soon got a P0171 - system too lean. LTFT was also hugely positive, near +10. So: the MAF was under-reading air, the rear o2 was seeing lean AFR, and the ECU was dumping fuel at the problem. On start the exhaust blew soot from how heavy this adjustment was.

Went to a scrapyard, bought another OEM box (which they absolutely butchered removing, big surprise) - for that dang pre-maf mesh. Installed, LTFT within +-3, back to normal.

Anyone with an intake on a 2.4i - take a look at your fuel trims on idle. I suspect intakes may throw off the MAF reading, and as the soot behind my car evidenced, the correction based on AFR at the rear o2 is anything but perfect. So intake users may be running a bit goofy.
 
#39 ·
Love the inline air filter idea. You've inspired me to try building one. I have a similar inline filter off of an old V8 Ford I'm going to try to adapt. You're volumetric efficiency calculations are off BTW, my N/A 2.4 is reading 123%Ve with just a custom exhaust. Theoretical maximum Ve on a NA 5cyl motor is 133% due to the firing order overlap compared to a 4cylinder motor.
 
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