Dyno Tested: Vacuum Tank Bypass mod
 

So I decided to try the Vacuum Tank Bypass mod that can be found here...somewhere

Did the first pull completely bone stock and made:
243.5 whp @ 5523 rpm
243.2 wtq @ 2678 rpm

Bypassed the vacuum tank and made:
250.8 whp @ 5454 rpm
254 wtq @ 2747 rpm

In my opinion, the gains are well worth the 5 minutes it takes to do the mod.
I also think I have pinned down what the vacuum tank actually does. IT COMBATS TORQUE STEER. If you read any car magazine comparisons of fwd turbo cars they always whine and moan about torque steer. So, if boost comes on slower, there is less torque steer.

My car now has 0 lag and it doesn't bog down in corners and prevent the car from making boost like it used to.

Picture of the dyno graph (Black=before, red=after)
http://i574.photobucket.com/albums/s...g/P1000667.jpg

Here's a video of the dyno run :cssNET:
http://www.youtube.com/watch?v=TeBXz4ngcUs

this is relevant to my interests

The hp increase could also be due to the engine being warmer in the 2nd pull and not due to the bypass mod, not the first time the lnf makes more hp on the 2nd or 3rd dyno pull.

Regardless, lag is essentially non-existent now and the car definitely feels faster.

When I bypassed it for a few days my fuel trims suffered.

Hmmm did you tune it out or did you plug the lines back into the tank?

Interesting...

Sub'd

Yeah, I'd be interested to know the details of the dyno session so that can be ruled out. (How long it sat before you all started, how long between stock pull and tank bypass pull, etc) That's surprising that it would make any change besides a response improvement.

Seemed to run a decent amount richer over much of the rpm range. Dont know how that could make it have more power though....

See how the A/F is about 13.0 in the midrange vs 14.0 on the first run that is why there is a power gain. All the Vac tank does is it stores air so that when you let off the throttle or get on the throttle it opens and closes the BPV much more smoothly.

i have a question term... would you say this would be a bad mod? or a good one... seems like one that you could do and retune your car vs the A/F

Not worth doing IMHO.
I did it to my car and what seems to happen is the BPV does not open as quickly as it should and that results in some mild compressor surge when letting off the throttle. I see no logical reason that this mod would change the A/F mixture unless a vacuum leak was introduced in the process. My commanded and actual A/F was always the same with or without the vacuum tank hooked up. All the vacuum tank does is to provide the BPV with a more consistant supply of air to either open or close it that is all it does. Chances are on his second run there was a little extra enrichment being added by the ECM to the normal PE Lambda value. That is the only reason the A/F should change in this situation.

Just try the mod for yourself. I for one love the way the car pulls now.

I don't think anyone is a fan of turbo lag.

The only lag we have the ETC lag really. It takes a full second from the time you go WOT until the throttle is open all the way to 100%. Made no difference on my car except it felt rough when letting off the throttle sometimes.

Was this done on a stock tune car too?

I had none of that. Just no lag. If I get the time, I'll try and make a video. That is if I can get someone squished behind my seat to hold a camera. So you can see how the car accelerates and how the boost comes on.

After watching the video again, I noticed their computer screen said my car spiked and held at 20 psi for a bit. I'm not sure if this is accurate because there was a sky redline there running a trifecta tune that read 5 psi higher than what his gauge showed.

I did this mod also and can confirm what you posted. :):):) By the way the adjustable pill mod also worked great for me.

That is strange mine never went any higher or lower when I did this mod. I was running my tune when I did it not the stock tune.

The OPs car has a stock tune.

Maybe on a stock LNF the mod works but with a tuned LNF the actual tune is controlling the boost. I dont have a clue im just throwing out some suggestions. I have been contemplating doing this myself but my SS is trifecta tuned at 23.5 psi.

My questions:

Is safe to do on a tuned LNF?

Is it worth doing on a tuned LNF? (any HP is worth it to me as long as it is safe HP)

Do i have to retune on my tuned LNF?

I did it on mine and then data logged it and sent the logs to Vince at Trifecta to have my tune adjusted for the higher boost. Im spiking around 25 a holding at 23 -24. It screams but I want to retune it with the adjustments from Vince before I take it to the track

Did you dyno it before and after the vacuum tank delete?

I wouldn't think this would be worth it at all.

I was only getting 17 lbs of boost before the mod with the tune. Thats why I did it. Like I said the car runs like a raped ape now. I just want to make sure the tune is right on. The Nittos really make a difference in the way the car hooks up also.

If you are stock, then maybe.

But if you are already going to tune, why not just tune it right and have your car run properly and blow off properly. High boost is ok until it has nowhere to go and blows through piping because it cannot release properly

the sky redline and solstice gxp do not have this vacuum tank and i assume are running the same bpv? the connection is straight from the intake, about 2 in of tube. so they are running this stock. of course they may have a different stock tune that compensates for this, but that i dont know. but as someone said earlier maybe for the torque steer from the fwd just my 2 cents tho...

The Solstice and Sky also didn't come with NLS from the factory, so I've supposed it was for NLS, to give the driver just a bit longer to shift before the bypass valve activates.

No matter why it was ENGINEERED for the car, it serves a purpose.
If you are looking to play, treat your car right and tune it properly, don't rig it and hope it isn't hurting anything

That dyno was runnin weird that day alex...

I don't understand the point of this.

well it seems like no one knows exactly what the system does or what this mod bypasses...so until then ill just keep it the way it was meant to be

I work with vacuum every day. We have vac tanks where I work to stabilize vacuum supply. Our cars have the tank for the same reason, I assume.

Per your comments (and others) this is what I had assumed as well. Those guys started using the Dejon spring to hold boost but I'm not sure if(or exactly how)this is related on our cars. Maybe an engineer will chime in:)-I'd love to have a definitive answer how Dejon spring/tank delete/downpipe wi cutout (or combination thereof) affects bpv operation/compressor surge. I'm currently on stock spring and I've never used the cutout-I hope I get more than extra noise and a cel,lol.

Regarding the tank delete: I bypassed tank only(not solenoid) and my results have been the same stock/stg 1-the car has less lag. Not sure how this traslates to better dyno #'s though?

1 more thing-if you do this mod keep an eye on your vac hoses-mine developed a leak at the solenoid and threw a post cat lean code; a little trimming/reclamping took care of it.

i did this mod 3 days ago and after driving my cra around it did change performance. less lag and it is holding at 15 and peaking at 17-18 before i was opeaking at 15-16 so there was an obvious improvement

From GM ..... Read part thats bolded


Service Information
Home Publications Number Search New Bulletins Bulletin Search Feedback Help
2009 Chevrolet Cobalt | Cobalt, G5 (VIN A) Service Manual | Document ID: 2324723
#PIP4669A: Intermittent DTC P2261 Setting - (Aug 10, 2009)

Subject: Intermittent DTC P2261 Setting

Models: 2008-2010 Chevrolet Cobalt SS
2008-2010 Chevrolet HHR SS

This PI was superseded to update model years. Please discard PIP4669.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Condition/Concern:

A technician may find DTC P2261: Turbocharger Bypass Valve Stuck Closed set with no problem found. It may be intermittent in nature or they may find the dtc will set after a hard acceleration, usually in third gear. DTC P2261 is a type B dtc and will not set on the first drive cycle the dtc sets, therefore multiple test drives should be performed to confirm repair.
Recommendation/Instructions:

SI diagnostics for this DTC states that the ECM compares the measured MAF reading to the modeled MAF and has detected a series of pulsations in the induction system that exceed a calibrated threshold. A snapshot of "Induction Data" will show the fault, however the tech may need to compare the snapshot data to another vehicle if they are unfamiliar with the readings. They should note a fluctuation and or a difference in the desired versus requested boost level. When diagnosing this dtc pay close attention to Circuit/System testing step #1. This step has you inspecting for any vacuum leaks, damage, restrictions, improper routing or connecting of the vacuum hoses on the charge air bypass valve solenoid, the charge air bypass valve, and the charge air bypass valve vacuum tank.

We have found leaking vacuum tanks causing this dtc. When testing the vacuum tank, care must be used or the results may not be valid. The vacuum tank has an integral check valve not noted in SI. To check the Vacuum Tank operation, disconnect the hose that runs from the tank to the Bypass Valve Solenoid at the solenoid and apply vacuum to the tank. The tank should be able to maintain vacuum with no decay. Note: If you remove the vacuum hose from the intake manifold and plug it and the decay stops the check valve is leaking, if the decay continues the tank itself is leaking.

Note: Front wheel drive platforms using the 2.0 Liter RPO (LNF) incorporate a charge air bypass valve supplemental vacuum tank. The purpose of the tank is to provide an instant source of vacuum to the bypass valve via the bypass solenoid (when it is commanded open by the ECM). This results in less pressure buildup under closed throttle conditions, thereby reducing compressor noise, surge and spool time.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.


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I would be scared to remove it... Seems like it is their to improve performance. If it is deleted is it easy to re-instal?

What are the procedures on doing that mod?

Hmmm.

Seems to be a placebo mod

No dyno close to me

I'm thinking about testing it out. Seems like it is designed to slow you down. I will need to talk to Vince

that write up made it seem to REDUCE spool time, the opposite of what people are claiming.
If someone is running BOV to atmosphere, I can see it working, but they are claiming improvement when stock.
That GM document makes it sound important IMO. Reduces dead air in the tubing, which decreases surge, thus reducing spool time.

Unless the bypass somehow still allows proper blow off...

Rukkee FTW(again)
I'm trying to wrap my head around this,lol. If the tank is bypassed wouldn't it be getting a more direct vaccum source(when commanded)? Maybe the mod helps when the bpv is moving in a certain direction,idk.
Regardless how the car felt this is straight from the horses mouth so I'm thinking F it. Still doesn't explain why it's not on the rwd's.

Unnecessary in vaccum/necessary in boost ?