# Often Overlooked: The Vacuum Reservoir.



## inivid (Aug 25, 2003)

In part-throttle situations, the vacuum reservoir/booster works in conjunction with the n249 valve to ensure there is always adequate vacuum to efficiently operate the diverter valve during any off-throttle situations; recirculating excess boost to prevent compressor surge. Due to the instant on/off nature of the n249 valve, there may not always be adequate vacuum for full recirculation of excess boost. Thus, a reservoir is incorporated in to the system. 

As ridiculous as this system may sound, it's actually quite brilliant, when you think about it. Given the purpose, one would think you would WANT to keep the vacuum reservoir in high boost applications, especially with a built cylinder head, as more aggressive cams tend to produce less vacuum in general. So, one would assume (due to drastic changes going from full/part boost to vacuum in BT applications vs stock) that less vacuum creation, in conjunction with a slower responding turbo would result in a significant difference in dv and wg response. Concluding that a proper vacuum reservoir would improve part-throttle response in daily driving scenarios for BT applications significantly, by ensuring full recirculation, keeping the compressor from partial stall, due to improper recirculation. 

just my analytical .02


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## dubinsincuwereindiapers (Jan 16, 2008)

I dunno... I dont see any other turbo car manufactures using one.... Just sayin..


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## inivid (Aug 25, 2003)

Because it's overlooked. lol 


EDIT: just reread what you posted. actually, many manufacturers utilize them.


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## dubinsincuwereindiapers (Jan 16, 2008)

inivid said:


> Because it's overlooked. lol
> 
> 
> EDIT: just reread what you posted. actually, many manufacturers utilize them.


 I believe you... Im totally talikng out my arse bro.. That being said.. I pulled mine a very long time ago, and no difference.. 210,000 on this turbo too..


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## inivid (Aug 25, 2003)

To clarify, many manuf. use them. Just NOT to the extent that the VAG 1.8T does. As I described, it stands to reason that daily-driven BT apps would benefit immensely from their utilization. It's been a massive misconception within the 1.8T community that it's entirely irrelevant. Something that only now has occurred to me, like a light-bulb switching on, like "oh duh."


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## inivid (Aug 25, 2003)

hasn't this occurred to anyone else?


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## Big_Tom (Aug 19, 2007)

I pulled mine off the other day and i didnt notice a diff. i don't miss it


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## l88m22vette (Mar 2, 2006)

Doesn't getting rid of the N249 negate needing the reservoir? I see where you're coming from with the N249 stuff but I noticed an improvement in my DV action and control as soon as I _removed_ the solenoid, and I would agree that removing just the vac reservoir made no difference, even though I was still using the N249 at the time. I would like to see results on a BT car, but all the same it seems like it will just create vacuum lag (because of having to fill the extra space), which contributes to that "spooky" feeling stock setups have. Another thing to think about is that the whole reason the N249 is there in the first place is to control the stock small-ass k03/k04s - the N249 pulses vac and vents while building boost, which (I assume) trys to negate the instant spool of those turbos to create an actual powerband


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## inivid (Aug 25, 2003)

After reviewing the layout of everything, it's possible to run the reservoir without the N249, as the N249 is only a fine-control mechanism. Without it, I'm sure the DV will have a more linear response, but in terms of vacuum, the reservoir/booster will still do it's job. Not so prevalent with stock turbo apps, but in applications where a larger, slower turbo is involved, a proper vacuum booster will ensure quick and full opening of the diverter valve to recirculate boost. And quicker, more complete dv response means less stress on the turbo. I doubt the effects would be perceivable, but they would nonetheless be there.


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## mescaline (Jul 15, 2005)

I don't have that  removed it some time ago along with 2kgs of junk under intake manifold.


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## Richard_Cranium (Mar 28, 2010)

i dunno about stock setups, N-75, J-55, N-249's or whatnot. i have always been a BT (if 57 trim is big LOL) from the start, on standalone.... 

BUT; the thought and theory seems sound to me. i can equate it to an old ride i had. it was a K5 2wd Blazer, hopped up motor, etc. i put an HO Vortec crate motor in it, on a carb, and some decent cams. it loped. it was badass, hence the email [email protected] LOL. 

anyhow (get back out of the past) i had to run an external vac reservoir on it, due to the lopey cam setup. it would not really want to hold brake power at idle, etc.... 

but again, i feel the theory is sound, and does have merit. real world experience with such; none here. sh*t, on both my race cars i even ditched the vac booster on the brakes, and run just a master cylinder off the pedal! stops fine.... well the rabbit did from 130+ 1/4 mile anyhow. yet to see the next one  

http://www.summitracing.com/parts/SUM-G1460/


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## robingohtt (Nov 6, 2005)

interesting read, man


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## Buschwick (Feb 12, 2007)

I've brought this up before but most guys here dismiss the idea that it's a really good system. 

Not only will it save some vac to slam the DV open whenever it wants, it also will react quicker than running straight off the manifold. 

Let's assume you're at 20psi and let off the throttle...there's measurable time from when you let off the throttle to the DV actually seeing a vacuum. The N249/vac res will bypass the time it takes the motor to pull a vac and slam the DV open before your boost even falls through 0. I think I'm the only one that can tell the difference in DV reaction times but with the N249 it DOES REACT QUICKER. But the psshhh sound without the N249 is a little more violent I think....I think it sounds better. But the N249 is much better for the turbo than running off the manifold. 

So, yes, this occured to me.


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## transient_analysis (Jan 28, 2003)

so.. you guys want to put together a diagram of the vac lines needed to use the n249 and vac reservoir? Keeping a non-stock setup in mind


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## Buschwick (Feb 12, 2007)

I don't know off the top of my head which port on the N249 does what but this is all you gotta do.


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## ypsetihw (Nov 20, 2008)

I agree with you in one sense - if you intend to keep the n249 system in place, then you should leave the vac reservoir connected because the system depends on it for vacuum and it will not function properly if you just cap it off. with that said, you can safely relocate the reservoir very easily, or you can do what I have done and bypass the n249 altogether, which means that the vac reservoir isn't being used by anything, and can therefore be safely removed. 

instead, I run vacuum directly from the manifold to the DV, and I find that it actually responds in a much more "natural" way than the stock setup. you can "feel" the turbo more because the boost behavior is more closely related to actual throttle position and entirely dependent on the manifold vacuum, and not some computer controlled vac circuit with a mind of its own.


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## transient_analysis (Jan 28, 2003)

thanks for the diagram Bruschwick.. Where does the extra brake booster port come into play?? 

This looks like a fun little project to try


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## Buschwick (Feb 12, 2007)

You don't need to use the extra brake booster line. I don't even understand the point of that. If you've removed all the crap from under the intake manifold then you should have at least one unused barb. Just run the vac line to the N249 all by itself.


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## ypsetihw (Nov 20, 2008)

or to the DV by itself


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## inivid (Aug 25, 2003)

The thought I've had from the start is a system that bypasses the N249, utilizing the vacuum booster/reservoir directly, by way of a simple system of check valves. Knowing that more aggressive cams actually produce less vacuum and larger turbos are slower slower spooling/recovering, the idea is to improve efficiency by utilizing the fore-mentioned. I think I've now phrased this idea a number of times, in a variety of ways, in this thread. Not sure if anyone is really getting it, based on the posts I'm seeing. 

Referencing the factory schematic, it wouldn't be as simple as the illustration posted.


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## ypsetihw (Nov 20, 2008)

we're not sure that YOU're getting it . . . you don't want to use the vac res without the n249 . . . the n249 can be thought of as a switched check valve. it has a Y inside that allows vac to be pulled on the reservoir, then caps it closed under boost. when the 249 gets the signal from the ECM, it flips open and provides vac to the DV from the reservoir. in the stock setup, the DV is NOT connected directly to manifold vacuum, but instead to the vac res through the n249. as such, it NEEDS the vac reservoir to function properly or you get lots of lag in the recirculation. 

maybe you are confused about how the DV actually works with the n249 bypassed . . . if you connect the top DV vac port directly to the intake manifold, then the vac port on the DV sees both vac AND boost. the boost helps keep it closed when you're boosting, and the vac opens it and keeps it wide open when you're sitting at idle. without the n249 which can take advantage of the extra vacuum that it has stored in the reservoir, the only way to improve the speed and reaction of the DV is to reduce the time necessary for it to receive a proper boost/vac signal, which means lessening the volume of area that needs to be compressed or evacuated . . . in other words, you gotta make a direct connection, and the shorter it is the better. 

as such, adding the reservoir back into the loop without the n249 just increases the area in which vac has to be created, hurting performance of the DV and anything else that receives a vacuum signal. it wouldn't add "extra vac", in fact, it would make it even slower reaching the appropriate level of vacuum. even if you put a check valve in line with the reservoir, without the n249 to redirect the vacuum properly, it will just sit there, holding vac all the time, again doing nothing but take up space. 

if you want to have "bonus" vacuum then you have to have some sort of vac reservoir and a signaling valve in there to keep the vac compartment sealed or it is just gonna fill with boost. voila, we're back at the stock n249 configuration . . . 

in conclusion - if you're asking just for hearsay, leave it alone. if you want to clean up the engine bay a little, relocate the vac res (i put mine on the battery cover) and run another vac line to it, and leave the n249 in there. if you wanna bypass the n249, just run a line to the DV port directly. 

I have pics from when I did mine, I'll dig em up and post


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## ypsetihw (Nov 20, 2008)

here's some junk: 










here's the relo - you can see which nipple to connect it to: 










seriously though man, just cap both the lines from the 249 and patch it to the mani where one of your brake boost lines used to be. works great.


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## l88m22vette (Mar 2, 2006)

ypsetihw said:


> instead, I run vacuum directly from the manifold to the DV, and I find that it actually responds in a much more "natural" way than the stock setup. you can "feel" the turbo more because the boost behavior is more closely related to actual throttle position and entirely dependent on the manifold vacuum, and not some computer controlled vac circuit with a mind of its own.





ypsetihw said:


> or to the DV by itself


 These replies FTW :cheers: 

I get what you guys are "saying" about the N249, but theory is theory (is internet banter), and how my foot and ass feels while driving around with my DV connected to my intake manifold is what I care about - it is quicker, more direct, more linear, and gives me the feel of the turbo's actions. 

edit: as a quick add-on thought, I also forgot to mention that I got rid of an intake honking noise I had with the stock setup. My OEM TIP/vac with an intake honked like a love-struck Canadian goose right around 4k, but it didn't go away until I ditched the solenoid and reservoir :rofl:


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## McBee (Aug 11, 2006)

l88m22vette said:


> These replies FTW :cheers:
> 
> I get what you guys are "saying" about the N249, but theory is theory (is internet banter), and how my foot and ass feels while driving around with my DV connected to my intake manifold is what I care about - it is quicker, more direct, more linear, and gives me the feel of the turbo's actions.
> 
> edit: as a quick add-on thought, I also forgot to mention that I got rid of an intake honking noise I had with the stock setup. My OEM TIP/vac with an intake *honked like a love-struck Canadian goose* right around 4k, but it didn't go away until I ditched the solenoid and reservoir


 These fu*kers wake me up and I want to take a bat to their head sittin' on that long neck like a tee-ball. One of the top 3 reason I hate Chicago.

As for being on topic, I see and understand exactly what OP is theorizing, but in reality I don't feel it plays a _significant _role in the longevity of the stock turbo. BT, might be a different story, but I still wouldn't bother.


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## l88m22vette (Mar 2, 2006)

lol, what are the other two reasons? Can I guess? Are they winter and construction?


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## dubinsincuwereindiapers (Jan 16, 2008)

McBee said:


> These fu*kers wake me up and I want to take a bat to their head sittin' on that long neck like a tee-ball. One of the top 3 reason I hate Chicago.
> 
> As for being on topic, I see and understand exactly what OP is theorizing, but in reality I don't feel it plays a _significant _role in the longevity of the stock turbo. BT, might be a different story, but I still wouldn't bother.


 I feel ya on the geese.. They are the suck. Here in PA we just walk outside, and shoot them. And yes I live in the city, and I still shoot them. I hate those fackin dirty azz birds


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## McBee (Aug 11, 2006)

dubinsincuwereindiapers said:


> I feel ya on the geese.. They are the suck. Here in PA we just walk outside, and shoot them. And yes I live in the city, and I still shoot them. I hate those fackin dirty azz birds


 Yeah, people would call the cops at the sight of a gun around here (suburbs). I do find shooting more fun and I've always loved firing off a few rounds. Hell, I would get up extra early just to sit on my porch, drink a coffee, and see what I could knock off before work.

I miss good old Indiana...


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## dubinsincuwereindiapers (Jan 16, 2008)

Lol!! Thats my point!! I live in the suburbs in a major city! Those bastards land in my pool. fortunately I have really high hedges around my property, so I wait until they hop out of the pool, and shoot them in my backyard.. Ive been questioned about the gunshots, and just played dumb. Of course being friendly with everyone in your neighborhood helps too


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## ypsetihw (Nov 20, 2008)

I still peg groundhogs with a 22 in my grandparents backyard in an upscale mansion filled development in Erie pa. Ah Pennsylvania, the south of the north lol


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## ypsetihw (Nov 20, 2008)

McBee said:


> Yeah, people would call the cops at the sight of a gun around here (suburbs). I do find shooting more fun and I've always loved firing off a few rounds. Hell, I would get up extra early just to sit on my porch, drink a coffee, and see what I could knock off before work.
> 
> I miss good old Indiana...


 no joke, I speced parts for a custom rifle rack on the trunk hatch itself, so when it pops up you could pull your rifle or shotty in down and out. Turns out it is super cheap if you wanna drill some holes lol


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## dubinsincuwereindiapers (Jan 16, 2008)

ypsetihw said:


> no joke, I speced parts for a custom rifle rack on the trunk hatch itself, so when it pops up you could pull your rifle or shotty in down and out. Turns out it is super cheap if you wanna drill some holes lol


 I dunno.. For some reason I like you a lot more now.. :thumb: lock, and load brotha


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## Buschwick (Feb 12, 2007)

l88m22vette said:


> it is quicker, more direct, more linear, and gives me the feel of the turbo's actions.


 It is not quicker. It's louder is about all...but the N249+vac res will rip the DV open faster than anyone's setup straight to the manifold. 

Why doesn't that make sense to anyone? It opens the DV before the TB is even done closing cause the ECU KNOWS what's about to happen. The DV doesn't have to wait for a vac in the manifold to open...this is why the vac res is there. It's keeping that vac stored to be able to do this while the manifold isn't even in a vac yet. We're talking about milliseconds difference but over time those milliseconds might add up to prolonged life of the turbo....or not...who knows. 

I'm not for it or against it cause I'm not even running an N249 either cause I like cleaner bays like most everyone. And with the N249 it does feel like it's not part of your throttling but the ECU doing it's own thing. 

Just saying that it is faster with it is all.


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## Buschwick (Feb 12, 2007)

ypsetihw said:


> no joke, I speced parts for a custom rifle rack on the trunk hatch itself, so when it pops up you could pull your rifle or shotty in down and out. Turns out it is super cheap if you wanna drill some holes lol


 

lol... 

you have to get rid of the fabric cover or whatever on the lid? That's awesome!


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## O_o (Nov 12, 2009)

dubinsincuwereindiapers said:


> I feel ya on the geese.. They are the suck. Here in PA we just walk outside, and shoot them. And yes I live in the city, and I still shoot them. I hate those fackin dirty azz birds


 ^^^ X1,000,000  

If ever there was a species that deserved extinction, it's those nasty-a$$, f**king honking green $h1t dispensers. They don't even taste good for fu*k's sake! Question: when I see people feeding them, which should I shoot first? 

Anyway, back on topic: isn't there enough vacuum in the lines to open the DV? I mean, there's still enough for the brakes, which I would think is by far the biggest consumer of vacuum... uh, if vacuum can be said to be "consumed".


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## bpfoley (Nov 30, 2000)

The brakes use their own vacuum reservoir called the brake booster that sits behind it's own one-way check valves.


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## McBee (Aug 11, 2006)

l88m22vette said:


> lol, what are the other two reasons? Can I guess? Are they winter and construction?


 Close. Construction is right, but winter is fine with me, although I could do without it.

1) Traffic/Construction
2) Too many people driving who shouldn't have a license. 
3) Geese

The list goes on...but these are the top three.


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## screwball (Dec 11, 2001)

I love the winter solely for the extra pep my car picks up. With a bigger turbo it's waaayyy more pronounced.


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## transient_analysis (Jan 28, 2003)

One thing that bugs me about the non n259 solution (i.e. manifold direct to DV/BOV) is the valve response at higher altitudes. My Tial stays shut at altitude with the 11psi spring, but is fine down at sea level. The 9psi spring is open at sea level on my car.. and I'm still running a MAF.. 

If the n249 and vac canister really do provide better DV response, and average out DV performance for different atmospheric conditions, I think modifying the system for a BT application could be worth it.. 

Anyone want to chime in on altitude thoughts?


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## ypsetihw (Nov 20, 2008)

I'm in Denver at ~5800ft at my house, I have a chipped k03s that makes around 19psi (max it can push up here because of the thin air). I have a forge 007 with the lightest spring in there, and it works great. I have noticed that you can get away with a softer spring at altitude


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## transient_analysis (Jan 28, 2003)

How do you have it hooked up? straight to the manifold, or through the n249 system?


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## ypsetihw (Nov 20, 2008)

transient_analysis said:


> How do you have it hooked up? straight to the manifold, or through the n249 system?


 I relocated mine with a homebrew pre-TB pipe, and it is connected directly to the manifold with a piece of vac hose about 6" long - it reacts SUPER quick, love it 

this is a pic before my catch can - the big radiator hose across the top is rerouting the boost, the DV is down next to the blue TB pipe just in front of the IM


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## ypsetihw (Nov 20, 2008)

if you wanna leave the DV in stock position and bypass the n249 (and also delete the vac res), just cap off the two outermost nipples on the n249 bracket (driver's side when looking at the engine bay - pictured below), leave the DV where it is connected to the stock hardline, and run a patch from the hardline to the intake manifold directly, bypassing the n249. then just remove the vac res and pull it off the hardline - keep in a box if you ever wanna put it back. 










and here's the diagram of the n249 bracket when removed - just for reference:


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## l88m22vette (Mar 2, 2006)

Self-whoring pic containing no N249/reservoir content  - this is exactly why I got rid of that crap, along with probably 10lbs of other random junk in the engine bay. Cleaner, easier to work on, fewer places for problems


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## sounrealx (Apr 4, 2007)

l88m22vette said:


> Self-whoring pic containing no N249/reservoir content  - this is exactly why I got rid of that crap, along with probably 10lbs of other random junk in the engine bay. Cleaner, easier to work on, fewer places for problems


nice kink in the booster line


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## ypsetihw (Nov 20, 2008)

sounrealx said:


> nice kink in the booster line


its the PCV line actually coming off the VC, but yeah I agree it SHOULD NOT be kinked like that

I dig the tucked injector harness though!


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## l88m22vette (Mar 2, 2006)

Its not that bad, its the angle of the picture...I'm going to be doing a bunch of crap in the engine bay this year and the catch can position and hoses are going to be redone


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## inivid (Aug 25, 2003)

the n249 delete, etc. has become such a fad that even when presented with a legitimate reason to keep it in BT apps (such as presented here), everyone is like "naw dawg, i READ on vortex that it doesn't do anything. plus it's cool to delete it and if u don't ur not baller." ...ridiculous and ignorant, imo, just how often people fail to research, poke, prod and find out exactly how things work. there is a reason for everything on these cars. yes, i will agree that some are useless fail-safes, with regard to stock turbo applications. however, in BT applications, some things can be exploited and improved upon to improve the efficiency of a BT setup. don't be a sheep just because some vortex-approved post-whore does it. i'm just sayin.


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## 1.8t67 (Dec 7, 2008)

my cams are pretty radical. at 10in/hg there is plenty of vacuum for the brakes.


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## ypsetihw (Nov 20, 2008)

inivid said:


> just how often people fail to research, poke, prod and find out exactly how things work . . . don't be a sheep just because some vortex-approved post-whore does it. i'm just sayin.


nobody has said anything resembling "naw dog delete it cause its BALLER." several of the responses have been well reasoned, factual, and interesting, and have nothing to do with the "fad" of just ripping off the vac res. that isn't even the OPs question or the point of this thread. I don't think anyone has argued that the system is useless, and the OP makes a good point, especially about BT applications. nobody who knows what they're talking about is disputing that.

so who's the "vortex-approved post-whore" that's supposedly leading the flock?


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## inivid (Aug 25, 2003)

simply a generalization, as there have been many instances of following the flock, over the years (ie software and one-off ecu tunes, exhausts, intakes, etc). like jason once said a long time ago, under one of his old screen names, "todays bandwagon, is tomorrows disappointment." 

i am the OP and i'm simply wondering, at this point, if anyone really gets IT. honestly, i'm waiting for someone with more knowledge than me to either tell me i'm crazy, or substantiate my claims, as i think they're quite sound.


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## ypsetihw (Nov 20, 2008)

yes, I think you're right that the n249 system works, and works FAST, and because of that, there are benefits of having it in the car, especially with BT. your theory about compressor surge probably holds some water, and if you logged carefully you could probably demonstrate SOME variance with and without the system. 

with that said, my whole point before was simply that trying to rework the stock n249 is probably more trouble than it is worth because, well, it works the way you want it to. just leave it in there. with that said, if you wanna do anything to it, just run it straight off of manifold vacuum. 

I totally agree that hacking apart the n249 or just ripping off the vac res and capping it (like many in the flock have done) is WRONG, and yes you have to put some thought into it. but that isn't to say that there are not other ways of setting it up.


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## 2002 GTI (Aug 22, 2006)

*Vac reservoir relocation..*

i was looking at the reservoir and was trying to see where to put it however, how can i remove the vac hose without tearing it up? what am i doing wrong? ty in advance for your help.


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## evilpat (Feb 26, 2002)

The reservoir only serves to provide the N249 with vacuum so when there is none or even just insufficient vacuum from the manifold the ECU can open the diverter valve. Kinda of a halfway between the traditional vacuum operated valve of older FI cars and the electronic valves such as those found on the new VAG engines. Being that it is all part of closed loop does it really matter if the DV is open or closed at partial throttle? It comes down to response speed of getting in and out of boost. (interesting to note that many people are even bypassing the electronically controlled valve claiming the mechanical valves are faster . . . ) Sure a computer theoretically can process and output at an incredible speed but the actual valve still has a mechanical component that has to be manipulated. The input into the control of the DV is still manifold pressure so with that in mind electronic control is redundant . . . it is there to limit or protect the motor by giving the ECU some control if all of the other systems in place go kaput.

I removed the N249 and vac reservoir years and years ago just to simplify how the system works. Less vacuum tubing and junk under the manifold = faster response and less stuff to fail and cause problems.


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