it doesn't give you more boost as such, it just brings what is available, in sooner, or abruptly, effectively directing some of the otherwise charger bypassed air to the charger earlier. You might liken it's sensation at the pedal or from the butt dyno, to something similar to the sprint booster type gismos which do similar to the throttle housing/pedal ratio giving a sensation of more power when it also isn't actually any more than what's available at the throttle body anyway, just being condensed due to what it does at the pedal where it is connected. I did say similar, well aware the throttle and BPV do different jobs, just the condensing of a component operation is basically what is going on.
the VGS is just using vacuum draw off the pipe serving the fuel pressure regulator located at the closed end of the inlet manifold instead of the vac port at the bypass/intake end of the manifold. Both ports off the manifold create the same vacuum really (I believe - not measured) but the closed end I understand is said to also see some small degree of boost? So helping the BPV react quicker? That's pretty much it.
it came about due to the pre facelift ECU it seems, a software issue, the ECU taking its instruction from the throttle pedal and sending the throttle housing to it's target position but overshooting and then correcting causing a degree of repeated butterfly fluctuation, the relocation of vac source is apparently to stop the BPV butterfly reacting to this vagary of the housing's target position due to its proximity, believed to be the cause of what was termed a yoyo affect noticed in a number of early cars.
Personally I can't say it seems that obvious to warrant finding a solution, but then I don't spend that long in the cars for it to become an issue I suppose, although I do feel there can be a degree of it in the later car too in a certain area, more of a wah wah sound in the exhaust than the yoyo complaint originally.
The VGS concept led to the stronger springs being used in the BPV's, and also some tying the BPV closed, even adjusting the butterfly to totally close off any air bleed the stop screw was permitting.
The end result is more fuel used, more charger noise, compressed intake air 100% of the time, pronounced urgency, the latter action for a smoother throttle response/power delivery once technique re-learned, and much improved initial acceleration due to a more abrupt torque delivery as a result of either of the three options, the latter being the one I would use personally.
For me I think ideally I'd just prefer the BPV delete with a cable throttle butterfly and TPS really.
I am interested in the affect on IAT with the last part actually, whilst I accept less air needing to be compressed due to the presence of a BPV equals less heat from its compression, I also have in mind that in the bypass state, flow through the I/C stagnates and could at least in my mind, potentially result in some degree of instant heat soak, so I considered that if there were actually still some additional off or low throttle rpm, proportionate yet still compressed air flow there, whether it might improve IAT recovery further or hinder it? I suspect the latter potentially at higher rpm overrun maybe but with a closed plate? Not so sure. It's an easy test I never did but will at some point when I remember, a simple cable tie initially and logs over the same run in both states is all it takes initially. Then I am also curious how a custom map would change the affect of such alterations, this one a cost exercise as I don't tend to mess with the maps but one perhaps worth exploring, again something for later. I haven't seen anything written about these specific considerations anywhere to date, so it is of interest at least to me ;O)
I could try to do a tune for a permanently closed BPV at some point (with bytetronik). I think that the stcok ECU wants to go to open loop as soon as it sees boost, and it would probably be on boost almost constantly. Could test the effect on IAT too, although I think that a closed BPV will keep the IC warmer.
With a standalone ECU with extra outputs you could probably replace BPV with a small drive-by-wire throttle body...
I don't think open loop is all the time, there is a transition felt to it iirc and there is a random EML from the downstream MAP sensor I believe on occasion, otherwise it had good feedback if prepared to accept something like ~21mpg haha, then that most likely reflected a yee hah element.
My other 53 has no bypass anyway, no provision for it, zilch, then it isn't running either yet. The black car I was going to look at blocking off for another reason, also never mentioned elsewhere, most likely never considered, that's for elsewhere later perhaps.
Those on track could be potentially at an advantage at least perhaps experimenting with tying them shut.
After three months of waiting I finally received my new ST XTA coilovers and was able to fit them on September with Micke. I also replaced the rear springs with 6kg ones.
As usual, there was also some problems during the installation and this time it was the front tyres rubbing against the coils. After some thinking, Micke realized that we can use my winter rims with little bit smaller ET.
With help of tcbw's 5mm spacers I was able to drive on track next week. Not too much extra space over there
Also driver's seat was changed to Sparco Evo L before track day. With the approval of the cat this time...
Next mod forced us to take the exhaust off and break some bolts during the process Exhaust hangers were replaced with Powerflex ones at the same time.