Hey guys, it’s me- the King of TL;DR, in with another novel.
*Skip to bottom for TL;DR version. You’re welcome...you lazy cretin*
I thought I would chime in on a recent mod that I’ve been able to experience for a little while now as well as tackle a couple of the typical complaints that result from a fair number of other Mini owners who do this mod.
The mod I’m referring to is the Vacuum Gain System mod (‘VGS mod’ for short) for 1st-gen R52/R53 Mini Cooper S’. I’m not going to explain how the mod works or post a DIY how-to. You can find out more about the nitty-gritty of it here:
During my quest to hunt down what I thought was a boost leak for my 2006 Cooper S (turned out my throttle body bracket was a tad bit crooked and interfering with the movement of my bypass valve), I decided to give this a shot to see if it would help at all.
Considering the mod took less than an hour in my driveway and only cost me less than $10 in parts from Advance Auto, I felt like it was worth a shot and if it had any negative effects, I’d just reverse it.
Let me start out by saying this: The mod works. The effect is noticeable.
Let me follow that by saying this: If you don’t handle change well, you probably won’t like this mod and I’m honestly curious why you’re even reading a post about a ‘performance’ mod in the first place.
With this mod, boost comes on decidedly more strongly and at earlier throttle input. Boost also seems to begin at a lower RPM than the stock setup, but does not increase total boost amount, which is limited by the pulley. I’m still tapping 10.1 psi at peak boost, but I am getting to the meat of the torque noticeably quicker than I was without this mod. I have a feeling this effectively mimics the effect of the Detroit Tuned bypass valve (to a lesser degree), but uses a different approach.
I can attest that with this mod, you will FEEL the torque more than before, as it comes on quicker and more suddenly. It’s less of a gentle “crest” and more akin to the sensation you get at the top of a rollercoaster when it hits that first huge drop. This increased ‘snap’ in the throttle/boost response will give your butt dyno the vapors and might even make it swoon outright. Even though I know that, on paper, my car hasn’t actually gained any power, I feel like it’s a noticeably more powerful car because of the, let’s call it ‘violence’, with which it comes into the torque now.
A.K.A., The torque steer is real, yo.
I would also like to note that this does not remove any of the accepted benefits of a supercharger in terms of throttle and boost response- in fact it amplifies those same benefits. But it does result in a larger contrast between off-boost and on-boost and may make you more aware of the fact that, despite the marketing hoopla of Superchargers Weekly (I made that publication up so don’t bother looking for them), the presence of a bypass valve means that these cars do in fact suffer from boost lag. Once you put on your big-person underoos and accept that fact, this mod can be very enjoyable once you make it past the driving tutorial, which I’ll cover below.
Are there downsides? Yes. Primarily that of linear vs binary boost development. The stock operation of the bypass valve allows a very linear accumulation of boost, easing you slowly and gently into the torque curve with very few surprises and allowing easy adjustment with the throttle pedal. This mod removes some of that finesse and creates a more sudden ‘surge’ effect. The adjustability isn’t gone, however. It just has a narrower window than before and requires a more skillful, conscious use of the right foot when modulating the throttle and ‘easing’ onto the boost, such as in traffic.
Which leads us into our first common complaint: Yo-yo. This mod was originally designed to get rid of the ‘yo-yo’ effect of the OEM pre-facelift bypass valve in which the valve would butterfly at medium throttle inputs at the start of the torque surge (around 2,500-2,800rpm). The added throttle response is just a happy side-effect of this mod attempting to repair that issue. Does it repair that particular issue? I can’t say, since I have a post-facelift R53, but I will say this: a weak spring is a weak spring is a weak spring.
Some people have complained that this mod (and the Detroit Tuned bypass valve), actually causes or exacerbates the yo-yo effect.
To those people, I want to suggest this: Try checking your foot.
The first two days I had this mod, I got yo-yo when accelerating in a relaxed manner and when putting around town at medium throttle. At first I fumed and tried to mentally schedule some time to reverse the mod. Once I calmed down, however, I began to empirically analyse when exactly this was happening and what variables could be labeled as common denominators. You want to know what I discovered?
It was my right foot. That traitorous dog and his band of backstabbing phalanges...
See, you and I, we’re used to a more gentle easing-into of the boost and our leg and foot muscles have gotten used to that as well. So when you suddenly get a more sudden shift in torque delivery, it pushes you back more than expected and you wind up subconsciously overreacting to that torque by easing up on the throttle. This causes the car to decelerate, the inertia of which causes your body to move forward ever-so-slightly and causes your foot to press back into the throttle, speeding the car back up again, causing you to once again lift off slightly and repeat the process until you grumble about crappy Euro quirks and lift your foot entirely and start acceleration anew with more conscious care. It’s basic pendulum physics and it’s so subtle that it easy to not realize your role in the event and to blame the car.
So if you experience Yo-Yo after doing this mod or installing a Detroit Tuned BPV, I ask you to pay attention to your throttle foot first before blaming the equipment. If you can confidently rule out inertial bounce of you, the driver, as a variable, THEN feel free to continue considering mechanical ghosts in the machine.
On that same vein comes the second common complaint: Loss of throttle modulation. Essentially, some people don’t like the more binary feel of getting more torque at once. These people were probably the ones Darwin warned us about. They complain that the throttle becomes an ‘on/off switch’ and they can’t fine-tune their throttle response and acceleration. To that I say: check the nut behind the wheel before blaming the mod.
Folks, redirecting the bypass valve to react to boost/vacuum from the intake manifold instead of just the raw vacuum of the primary vacuum line doesn’t actually do a damn thing to your gas pedal. It just changes where and how the bypass valve gets its signal pressure.
Your throttle pedal, electronic or not, is unchanged and still has the same range of adjustment that it used to. The difference is that the torque curve builds and peaks more steeply than before, effectively shrinking the ‘window’ during which those certain adjustments can be made.
To simplify this: the car makes power faster, therefore your foot-brain needs to react faster to manage said power. It’s not the car; it’s you.
Have I had a positive experience with this mod and do I recommend it? Yes. But understand this: I had to go through a period of adjustment during which I had to set my ego aside long enough to re-learn how to modulate the throttle pedal and admit to myself that I’m not a perfect genius savant of all things driving-related. Not that I’d ever admit such a thing on the internet, of course. ;-)
TL;DR VERSION, as promised: Cheap and easy mod that works. You won’t gain any HP or TQ on the dyno sheets, but it will give you a more aggressive torque curve and snappier throttle response. Your butt dyno will be utterly effervescent with excitement and/or free Chipotle. You may have to deal with an adjustment period, though, during which you’ll need to get used to a smaller window for mild throttle modulation. If you get ‘yo-yo’ during this period, make sure it’s not just your foot moving back and forth due to acceleration/deceleration inertia. MOD WILL NOT FIX A BYPASS VALVE THAT IS ALREADY BAD OR BROKEN. SPEND ACTUAL MONIES AND REPLACE THAT THING. See here for details on the mod itself: http://www.northamericanmotoring.com/forums/how-to/…