there is another thread on NAM discussing a possible downside to this mod- higher exit temperatures from the intercooler, which would imply an overall reduction in performance of the vehicle. I am definitely not the expert on this like many of you, but I thought it might be worth discussing possible downsides. How long (miles) has everyone had this mod on their car?

btw...i have this mod on my MCS and really enjoy it. I will be receiving a 60mm test TB from M7 later this week and will be removing the VGS to evaluate. I will then reinstall to give my $0.02 on the difference.

 

Your temps will only be higher than stock at very light throttle application. When you need power and push down on the loud pedal, the bypass valve is closed, just like stock, so temps should be identical.

 

When the SC compresses the air, it gets hotter. When it decompresses when the BP valve is open, it cools. If the valve is open less, more of the time there's hotter air going through the IC. This isn't because of the VGS directly. If you do the RPII or RPI (wire tie it closed), you'll get the effect of adiabatic cooling less, and never, respectivly. But you get more power at lower RPMs. You choose.

Matt

 

Dr: adiabatic means without loss or gain of heat, but we get the drift.

 

So as the pressure changes, the temp changes. Adiabatic expansion and comression are conserved energy changes, and while no heat is added or extracted, the temp changes. Think about gasses expanding into a container with perfectly insulating walls. This is adiabatic expansion.

here is a link....

Matt

 

thank you sir.

 

And I got the TB yesterday. Thanks for the fast shipment.

I'd actually found a different link first, but it hurt as it starting taxing my mind with the different types of free energy, and all the thermodynamics that I did so poorly with in grad school. Even if I can't spell the concept, I still remember a bit of it.....

Matt

 

I found easily understanding thermodynamics a matter of taste, never tasted too good to me. Special relativity same way. For both, math always undergrad level but theory could be stupefying. I liked E&M and mechanics.

 

at the mysteries of quantum mechanics for hours. Mother nature is one crafty lady! It's like classical music, variations on themes. Mechanics makes so much sence, E&M was harder (have to use cross products and vector transformation), but quantum and relativity really blow ones mind!

It was wierd, I could handle thermo from the many body perspective (stat mech) much better than the trad thermodynamics route (but I did love how entropy influences behaviors!)

I know, I'm sick. But I did well in the nerd test!

Matt

 

Hello, just wanted to mention that while removing the VGS from my car, I noticed that my vac hoses hardened up under everything. The connection to my fuel press. regulator looked bad, the hose looked as though it was being pulled to the side or something, pretty sure it leaked at some point.

I removed the VGS because of this jerking I felt every time I let off the accelerator during a recent trip to the Sierra, never felt it before, having been up there thousands of times before installing the VGS, thought it or the condition of the hoses had to be the culprit.
Anyways, I confirmed that the hose I used was indeed vac line, not sure why it got so stiff after only a few months though, but though I'd share.

have a good day all.

 

Bah, I hated freshman dynamics class. Now that was horrible. Yet senior level machine design was easy. Go figure, course it's fun to watch as your senior professor plays with a pendulum in class (a big 1" nut on a sting) then hits himself, you guessed it, in the family jewels . Was quite ammuzing, course he gave us a pop quiz right after cause he didn't find it funny

 

Hopefully this is not too dumb of a question but... remember the 'ol M7 restricted valve by-pass tubing trick about a year and a half ago? This also was intended to smooth out low end throttle response. Can anyone compare the two or am I comparing apples to oranges?

 

I did extensive testing of the M7 "device" and it did nothing. Search for threads on the subject.

 

Andy,

Unrelated to VGS ... would you be available for an "offline" consultation regarding a concept I am developing? PM me if you would be willing...

(your PM inbox is full)

Theo

 

Sure, email me.

 

Will do...thanks!

 

anyone got a pic of the tubing they are using for the vgs mod?

 

I'm no longer using the mod, however.

 

I had posted earlier that I had installed the VGS on my '05 MCS, and I wanted to update folks that I have also removed my VGS.

MY reasons were pretty simple: with the VGS the bypass valve stayed closed longer, and when shifting under high-load (accelerating hard, etc) the bypass valve would stay closed just a nano-second too long causing some wicked engine-braking effects. This had the effect of causing a big JERK in between shifts, which felt like it was going to break something.

I drove around for about 2 weeks with the VGS just to be sure, and indeed I noticed this behavior pretty often. Once the weather turned cold this effect got even worse, and it finally got bad enough I was worried about the tranny, so I ditched the VGS, and I have to say, I am very happy I did.

Also, my mileage was worse with VGS, I think because the supercharger was working more often... or because my right foot was. Not sure.

On a final note, there was always something about VGS that I couldn't really verify easily, but it always felt like the last little bit of "omph" was missing when on the highway... like if I REALLY wanted to pass a 18-wheeler or something. With VGS there just wasn't anything there, and now without there is a last little bit of accleration waiting waaay down at the bottom of the peddle, which is awesome.

Anyway, it was an easy mod, and I'm glad I did it...

RM2k5

 

Anyone else experience these things???

 

IMHO....

I think that the VGS makes the bypass valve operate in a more "binary" manner with respect to throttle angle vs. boost: the BPV seems to be closed or open with not a lot of "semi-open"/"semi-closed" feeling at partial throttle angles.

I have noticed that in order to get the full effect of the VGS activating the BPV, I need to increase my throttle angle (step on the gas pedal harder). It seems like the BPV goes from fully open to fully closed in an instant, but once that is done, the BPV stays shut until I lift. Conversely, when I lift the throttle, the BPV goes from fully closed to fully open very quickly. I believe this effect has been felt by a number of folks and manifests itself in posts with a number of analogies.

The stock vacuum activation is, I believe, more gradual in its operation. This means that lower throttle angles may partially activate the BPV beginning to close sooner. Thus, this effect may be interpreted as more low-rpm power. However, at the same rpm level, the same effect can be felt with the VGS if you fully depress the throttle.

So for me, I have had to "retrain" my right foot and slightly modify my shifting technique to take advantage of the VGS. I understand that some folks might not want to do that; to each his own.

Also, my gas mileage has gone down from a calculated average of 25.7 mpg to 24.2 mpg within the same season. My MCS ia an '04 with 30k and JCW 210 kit.

Theo

 

I haven't had any issues like this. And to complicate the issue, two different SC tuning books I've read show bypass valve operation controlled a la VGS, not the stock configuration. Also, in thinking about the stock configuration, as the by-pass valve opens, air going from the high pressure side of the SC to low pressure side will raise the pressure there, and this gets mixed up in the TB control loop, and all sorts of stuff can happen. To me, the stock set up just doesn't make any sense, and seems like it would be prone to oscillation (can we say yo-yo?). So I'm baffled. Any chance that there were leaks? either under vacuum, or more likely leaking boost? I ended up wire-tying the connections, just out of paranoia.....

Matt

 

To add to this, lemme remind us all: The '05's went to a system very much like the vgs. It uses a stronger vacuum source, which I've heard is the same one, actually....

 

I agree with both the Dr. and Koopah. I've used the VGS on my '05 for some months now, and not experienced any of the negative aspects reported by Rallymini2005. The description of the more "binary" operation of the BPV on acceleration, however, does seem accurate. I like it like that - it gives a more immediate, sports-car feel when you hit the gas. I haven't measured any drop in gas mileage, though.

 

Different vehicles/drivers have different experiences/needs with the VGS. That's why I recommend installing it in such a way that you can easily swap it back to stock behavior (cap the long vacuum line you installed) to see if it works for you or if stock configuration is preferable. Personally, I can't stand the yo-yo feeling every time I switch back to stock.