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  • Stack Swap (Content For Debate)

    Today, we’re going to see whether or not velocity stacks by themselves make any additional power to a motor, specifically the S62.



    First off, we at Fluid MotorUnion feel we need to say this right away: This is not marketing material. This is not meant to promote sales of our product. This was not made as an attempt to compare our product to any competitor. This video is merely to open a dialogue with the aftermarket community at large.

    That being said, the following video is a one-take shot that’s meant to promote a dialogue as to whether or not the stacks by themselves make power. Often times, our stack systems are incorporated into larger builds with ECU tunes that don’t allow for a way to measure the gains directly from the stacks (sans tune).

    Now, power was not our goal when we decided to start investigating different velocity stack designs. Our original goal, one which we believe we’ve achieved, is to give the vehicle a more aggressive and unique sound that’s impossible to replicate on cars without individual throttle bodies (ITBs). Over the years, we’ve played with multiple designs (roughly 8 different ones — short stacks, long Medusa-style stacks, etc.). During our R&D, our engineers have calculated the proper stack length by finding the optimal wavelength to base them upon, and we’ve found that this design we’re currently using is making the most power while still keeping the sound where we want it.

    As you can see from the above video, we first did a walk-around of the car to show that there are no laptops or wires running into the car that could apply a different ECU tune to the car while Craig is changing out the velocity stacks. We have purposefully tried to show as much of the room as we can in an effort to remove any potential doubt those viewing the video may have (and trust me, we’ve anticipated a good amount). There’s also a clock on the left of the frame, with a second hand, to show that no editing trickery took place at any point; this is one continuous shot. It would obviously be in one’s benefit to watch this at the highest resolution possible (720p, fullscreen).

    While we filmed the dyno room with our Sony Handycam, we also ran CamStudio on our dyno’s computer to record the dyno’s output at the same time, which we synced with the dyno room footage in iMovie (as best as we could, we may be off by a few fractions of a second on the sync). The picture-in-picture doesn’t go away to show that it’s one continuous recording of the dyno output. The small blip of power in the graph of the first stacks-applied run is consistent with the sound and performance of the motor in the dyno room shot, again showing that we’re not trying to pull a fast one on anyone here.

    We also are the first to admit that there are drawbacks with running open stacks. The purpose of this video, once again, is not to show our system’s superiority over all closed-airbox designs. Whether or not you choose to run open stacks is up to you. We take as many precautions as we can when running them so as to minimize (but not eradicate) any potential issues.

    Regarding the hood being open versus closed, we did later runs with the hood shut, and found no difference in how well the bolted-on stacks performed. It just wasn’t filmed all in one run, so it wasn’t included in this video.

    Regarding the vehicle’s initial power output, the only modification to this vehicle is the Fluid MotorUnion axle-back exhaust, which deletes the mufflers in favor of pass-through resonators. The typical term for a motor that puts down stock numbers like this is “factory freak.” The initial power is not indicative of an ECU tune being applied to the motor.

    For the sake of consistency in testing, we did this entire run with the MAF sensors unplugged, allowing the vehicle to throw a CEL and enter its alpha-n programming. We did later runs with the MAFs plugged in during the initial runs, and found no difference in average gains. Once again, it wasn’t filmed all in one shot, so it wasn’t included.

    And for those of you still worried about a tune being applied to the ECU for this video, the loss of torque and power early on in the powerband should be an indicator that BMW’s stock map was used for this setup. Our stack-specific tune removes this loss of early power while still retaining the power and torque gains at the late end of the powerband. Low end loss can be removed through tweaking the camshaft timing along with a couple other tricks.

    Once again, as we did in the beginning of the text, we need to really drive this point home: We are not using this as a shill for our velocity stack products. We are not employing any tricks to get you to believe that you should buy our stuff. We’re merely trying to show that, from our testing, bolting on a set of velocity stacks will produce power, and we want to open a dialogue with those who may not have believed this, as well as those who may still not believe it. If you have any questions or comments, you know our doors are always open for a dialogue. Now enjoy the video!

    [ame="http://www.youtube.com/watch?v=3neHy4kZjDg"]http://www.youtube.com/watch?v=3neHy4kZjDg[/ame]

    www.fluidmotorunion.com
    www.stanceworks.com



    Originally posted by Oxer
    I'm pretty sure I will molest any exhaust systems you leave lying around

  • #2
    Dope. What RPM range are you guys trying to make peak additional power? In my (totally expert opinion ) it seams like the stacks could be a little longer to lower the resonant frequency of the system. I'm sure you guys have experimented to find the best length as a function of wave number or frequency or whatever. I'm only curious because I study acoustics in school and pipe acoustics is one of the fundamental concepts.

    Either way resonance effects are cool as hell, don't even get me started on 2 stroke tuned pipes....
    Word

    Comment


    • #3
      Originally posted by SmokeyTheBear View Post
      What RPM range are you guys trying to make peak additional power?
      ^this, and:
      do you use these in combination with different exhaust manifold runners?
      what are your valve to common air lengths?
      what kind of VE numbers are you running?
      It seems from your description, you are retarding cam timing to negate the power loss at low rpm, is this not effecting higher rpm VE?
      If you are tuning runners for higher rpm, why are you not advancing cam timing to complement?

      Why are you trying to justify power gains? I would hope that most people considering your system would be interested for its tuning effects, not the madtyteeurobawsebetterthannawse type.
      Last edited by gambit4000s; 12-24-2011, 08:42 AM.

      Comment


      • #4
        Huh. Think this will shut up those who said you couldn't get 20whp out of stacks?
        Steve - now in San Diego!

        Shoot My Car - Automotive Photography in SoCal

        Comment


        • #5
          Sorry the replies were a bit late, folks; I had a 3-day weekend off for Christmas and essentially shut myself off from the car forums.

          Originally posted by SmokeyTheBear View Post
          Dope. What RPM range are you guys trying to make peak additional power? In my (totally expert opinion ) it seams like the stacks could be a little longer to lower the resonant frequency of the system. I'm sure you guys have experimented to find the best length as a function of wave number or frequency or whatever. I'm only curious because I study acoustics in school and pipe acoustics is one of the fundamental concepts.

          Either way resonance effects are cool as hell, don't even get me started on 2 stroke tuned pipes....
          Resonance effects are crazy. We actually found a system online in some guy's race car that has an adjustable-length stack setup, with the runners becoming longer or shorter based on a few different variables we believe (he didn't give away all his secrets in the video description).

          We've actually had quite a few different S62 stack designs of various shapes, materials and lengths. We found this one to best suit our goal with the stacks.

          We sell all our stacks bundled with an ECU tune in order to make up for the stacks' loss of power and torque at the low end, but since we kept the ECU stock for the experiment, we couldn't make up for that loss. But our goal was to show if gains were present with the stock BMW maps, and for this specific experiment (along with others performed not in front of a video camera) there were positive results. We don't recommend installing the system without an accompanying tune, which would obviously result in power/torque gains at all points in the revs.

          Originally posted by gambit4000s View Post
          ^this, and:
          do you use these in combination with different exhaust manifold runners?
          what are your valve to common air lengths?
          what kind of VE numbers are you running?
          It seems from your description, you are retarding cam timing to negate the power loss at low rpm, is this not effecting higher rpm VE?
          If you are tuning runners for higher rpm, why are you not advancing cam timing to complement?

          Why are you trying to justify power gains? I would hope that most people considering your system would be interested for its tuning effects, not the madtyteeurobawsebetterthannawse type.
          When we install our stacks on our cars (or when we sell sets for customer cars), we always include an ECU tune to alter the timing and air/fuels such that gains are consistent at all points in the powerband.

          Most of the time on the forums, when we have systems with stacks installed, people will quickly rise up to point out that the act of installing the stacks does not produce any power, that it's all in the tune and just bolting on stacks won't produce a single hp gain.

          THAT was the main line of thinking that we were attempting to challenge in this experiment. We weren't setting out to prove our system is better than any specific one, we just wanted to see if the nay-sayers were right. That meant keeping every single variable consistent other than the physical intake (ECU tune, airflow, ambient temperature of the room, etc.). That's why we filmed it in one take -- so that people wouldn't accuse our experiment of being tarnished through some sort of trickery (like installing an ECU tune while switching out the stacks).

          So basically the only reason we're trying to "justify" the gains is to open up a dialogue with all the armchair scientists that strongly believe that the stacks alone (independent of a tune) do not produce a single inch of extra power.

          We believe that anybody who purchases the stacks, like you said, isn't as interested in the "omg massive power" as they are in the unique sort of sound that can only be produced through open velocity stacks (not enclosed in a plenum). At that point, the power from the stacks and ECU tune are merely a benefit to having the system.

          Originally posted by Aitch View Post
          Huh. Think this will shut up those who said you couldn't get 20whp out of stacks?
          Our goal was never to "shut anyone up," but rather to open up a dialogue with those who didn't believe the notion that the stacks by themselves were the result of any power gains. We're not saying it's going to be 20 whp for all ITB-equipped BMW motors, as this was merely one small example, we're just saying that from our testing (and without any sort of funny trickery), these are our findings. It's nothing more than experimenting to attempt to prove a hypothesis.

          www.fluidmotorunion.com
          www.stanceworks.com



          Originally posted by Oxer
          I'm pretty sure I will molest any exhaust systems you leave lying around

          Comment


          • #6
            how about running a baseline without the stacks and without the air box to show how much of or if the gain came from just removing the airbox and filter restriction.

            Comment


            • #7
              ^^This.

              I would have liked to see you do a dyno run with no stacks and no airbox. I would expect hp gains just by removing the factory air filter and box due to reduced airflow restriction to the ITB's. This would show that your actually making more power due to stack design and not just by having a more free flowing intake.

              You never specified where the target RPM range was for the stacks, obviously with a tune your going to be able to take advantage of the increased airflow to the ITB's and make more power across the band. The point of running stacks is that you produce more power due to a pressure wave at some rpm, ie the air pressure at the ITB is greater than the ambient pressure around the car.

              I'm not trying to **** on FMU or stacks in general as i'm a huge fan of both. I think its great that you guys want to show that stacks produce more power, I just wish that you offered a more fair comparison. You say the goal of the video was to show that by bolting on a pair of stacks you gain more power. Then show it without stacks (no airbox, straight ITBs) and with stacks.

              Originally posted by FluidMotorUnion View Post
              Resonance effects are crazy. We actually found a system online in some guy's race car that has an adjustable-length stack setup,
              Link?
              Word

              Comment


              • #8
                Originally posted by SmokeyTheBear View Post
                ^^This.

                I would have liked to see you do a dyno run with no stacks and no airbox. I would expect hp gains just by removing the factory air filter and box due to reduced airflow restriction to the ITB's. This would show that your actually making more power due to stack design and not just by having a more free flowing intake.

                You never specified where the target RPM range was for the stacks, obviously with a tune your going to be able to take advantage of the increased airflow to the ITB's and make more power across the band. The point of running stacks is that you produce more power due to a pressure wave at some rpm, ie the air pressure at the ITB is greater than the ambient pressure around the car.

                I'm not trying to **** on FMU or stacks in general as i'm a huge fan of both. I think its great that you guys want to show that stacks produce more power, I just wish that you offered a more fair comparison. You say the goal of the video was to show that by bolting on a pair of stacks you gain more power. Then show it without stacks (no airbox, straight ITBs) and with stacks.



                Link?
                Originally posted by boostncosworth View Post
                how about running a baseline without the stacks and without the air box to show how much of or if the gain came from just removing the airbox and filter restriction.
                You both present an excellent point for comparison. That's definitely an idea to consider incorporating into a future "experimentation" video. As I sit here and mull the idea over, I like it. The only reason I could possibly shrug at it is because it's not a style of intake typically run on the street (i.e. nobody runs a totally open airbox on the street), but in terms of comparing it to how BMW's stock alpha-n map runs with the stacks and OE plenum, it's definitely good food for thought.

                www.fluidmotorunion.com
                www.stanceworks.com



                Originally posted by Oxer
                I'm pretty sure I will molest any exhaust systems you leave lying around

                Comment

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