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Discussion Starter · #1 ·
I may be wrong here and maybe there isn't much to be gained but for those of us with improved intake piping and the stock airbox it seems the stock inlet snorkel is a significant bottleneck. I have improved everything from the filter to the intake manifold (except the turbo) - K&N panel filter, ECU spacer, 3" Snabb intake pipe, Elevate intercooler hardpipe, large capacity FMIC, Porsche 70mm TB, ported OE upper intake, and ported and polished OE lower intake manifold - so when I look at the small inlet snorkel and 2.65" diameter flex tube leading to the airbox I'm left to wonder if that is limiting everything. I've searched here and on C30crew but didn't find anything on replacing the stock snorkel/tube while retaining the stock airbox. I don't want to go as far as a whole new filter system, and I don't want to chop new holes in the front of my car so I'm left with trying to develop something compatible with the airbox and the existing opening in the front section above the radiator.

The opening to the airbox is odd shaped but somewhat large - 3.6" across one way and 2.9" the other - but the piece that connects it to the flex tube reduces to around 2.65" after a 90 degree bend. I picked up spare inlet pieces from a wrecking yard and I found that a 3.5" ID silicone tube has about the right circumference to attach to the piece exiting the airbox if I cut away the rest of the piece. My plan right now is to use a 3.5" ID 90 degree silicone elbow to attach to the cut-down piece, a length of 3.5" OD tubing (PVC or aluminum), then a 90 degree 3.5" ID - 4.0" ID silicone elbow to replace the snorkel. I think the silicone elbow can be deformed so it fits over the front bulkhead and under the hood while providing significantly more cross sectional flow area than the stock snorkel. I'm still working on ideas for the piece to go through the hole in the front bulkhead and into the area in front of the radiator as well as how to attach the 4" elbow to that piece.

I'm still in the planning and gathering parts stage so I don't have any pictures but as soon as I start to put it together I'll be sure to take plenty. Any thoughts on these plans, or has anyone already tackled this?
 

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At least in the Subaru world, it was pretty much accepted fact that the stock intake box was adequate for up to about 300 WHP. I ran an AEM CAI for a while at 275 WHP but tired of the constant noise for the questionable gains it provided.

Of course since we're talking completely different platforms, YMMV.
 

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The best way to determine if the snorkel is an issue would be to place a manometer in front of the air filter and see if it registers a negative pressure relative to ambient. I don't recall anyone having done that yet.
 

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Discussion Starter · #5 ·
The best way to determine if the snorkel is an issue would be to place a manometer in front of the air filter and see if it registers a negative pressure relative to ambient. I don't recall anyone having done that yet.
I have been searching for a wireless sensor to do just that but I haven't found anything that seems appropriate. I'd like to be able to measure the vacuum/pressure under a wide variety of conditions (although WOT on the freeway may be the only relevant condition) for both the stock inlet and any modified inlet I create. Maybe the easiest solution would be to get a really long rubber hose, snake it through the snorkel into the area by the filter, and then route it into the passenger compartment to a vacuum gauge. It would be a temporary setup so wouldn't to be too clean as long as the hose doesn't come near anything too hot or spinning.

Cut out the front of the snorkel so incoming air goes directly in and up instead of being drawn in from the side
I should have included that in the list of mods. I took out the whole baffle piece so now there is just the piece that attaches to the snorkel. This inlet is around 6 square inches which is equivalent to about a 2.75" diameter round tube so it's still smaller than the 3" turbo intake pipe.
 

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I think this mod is going to be more for personal aesthetics more than anything, just make something you think looks good i cant imagine you'll see or notice a drastic change in performance on top of your current mods.
 

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Discussion Starter · #7 ·
I think this mod is going to be more for personal aesthetics more than anything, just make something you think looks good i cant imagine you'll see or notice a drastic change in performance on top of your current mods.
Yeah, you're probably right. It just bothers me that for all the effort to improve air flow into and out of the turbo it still has to suck air through the same size snorkel and tube as used on the 2.4i engines. I don't have a good seat-of-the-pants feel for performance improvements so it would be nice to be able to measure the negative pressure in front of the air filter to see if the stock air inlet is a limiting factor.
 

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Sounds like you might also want to measure pressure in the intake tube after the MAF. But be careful there that you position the pressure sensor so you don't get ram or Bernoulli effects at the end of the tube.

I do think these are trivial effects but only data can tell.
 

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The polestar concept c30 uses the focus rs intake pipe and they cut out the battery vent into the grill and hid the entire 2.5in intake behind the grill so it looks clean. Or cut out the grill like I did.
 

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Discussion Starter · #10 ·
Sounds like you might also want to measure pressure in the intake tube after the MAF. But be careful there that you position the pressure sensor so you don't get ram or Bernoulli effects at the end of the tube.

I do think these are trivial effects but only data can tell.
I wonder if datalogging the MAF reading would give relevant information? Since the idea is to make it easier to get air into the engine shouldn't it show up in increased mass air flow at the sensor? I haven't researched these statements so I could be completely off base!

The polestar concept c30 uses the focus rs intake pipe and they cut out the battery vent into the grill and hid the entire 2.5in intake behind the grill so it looks clean. Or cut out the grill like I did.
I saw your intake in another thread and like what you did but I'm leaning toward using the stock airbox and air inlet location.
 

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I wonder if datalogging the MAF reading would give relevant information? Since the idea is to make it easier to get air into the engine shouldn't it show up in increased mass air flow at the sensor? I haven't researched these statements so I could be completely off base!
I'm not sure how you hold the zillion other factors constant, in order to use the MAF value for this. If you've got an idea, I'm all ears.
 

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Minor modification... I'm pretty sure others have done this. I'm not worried about debris getting into the snorkel since it just feeds a duct to my cone filter. I was also trimming the bumper grill anyways to fit the do88 so I figured why not.


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