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    • N63 versus N63TU part II - Aftermarket downpipes hurting performance? Factory ECU reducing boost over 5000 rpm?

      A couple of weeks ago BimmerBoost published Dynojet results from BMS (Burger Tuning) showing the baseline difference between an N63 V8 in a 550i and the updated N63TU V8 rated at 45 more horsepower in a 2014 550i. The N63TU showed less power than the N63 V8 even though BMW rated it at 45 less horsepower. The caveat is that the 2014 550i had aftermarket catless downpipes and those seemed to be causing a power loss.

      BMS did further testing on a 2014 550i that had the stock exhaust pieces in place and the results below 4500 rpm were about the same. Above this RPM though the car without downpipes showed more power. The power once tuned however is about the same between the two.

      Here is a Dynojet graph comparing a 2011 N63 based 550i and a 2014 N63TU based 550i both with stock downpipes. The N63TU shows a smoother torque curve and a good amount more torque especially from 2700 to 4500 rpm:


      Here are the N63TU tuned values on the 550i with the stock downpipes (transmission shifting issues prevented dyno measurements before 4000 rpm from being picked up:


      Here is the tuned N63TU with aftermarket downpipes from before showing slightly more torque although slightly less peak horsepower than the car without aftermarket downpipes:


      What is the explanation? BMS states the factory ECU is reducing boost in both stock and tuned form above 5000 rpm. Why? That is anyone's guess. BMW seems to have designed to the ECU to reduce its boost target in that RPM range. It is going to take further tuning to eliminate this and at that point aftermarket downpipes should show gains but as of right now the ECU is reducing boost stock, tuned, downpipes, etc.
      This article was originally published in forum thread: N63 versus N63TU part II - Aftermarket downpipes hurting performance? Factory ECU reducing boost over 5000 rpm? started by Sticky View original post
      Comments 13 Comments
      1. blkclk550's Avatar
        blkclk550 -
        i actually ran slower times with my Catted AR down pipes so i had to bring the boost up to match my previous times with out the down pipes.
      1. Terry@BMS's Avatar
        Terry@BMS -
        There is definitely something going on with that particular n63tu downpipe car's top end boost. I can't be sure it's downpipe related and since he's the first n63tu with downpipes we've tested I suggested he remove them for a follow up dyno just to be sure.
      1. blkclk550's Avatar
        blkclk550 -
        My 3 inch exhaust going on this week will redyno on same mustang dyno as before.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
        There is definitely something going on with that particular n63tu downpipe car's top end boost. I can't be sure it's downpipe related and since he's the first n63tu with downpipes we've tested I suggested he remove them for a follow up dyno just to be sure.
        But what exactly is going on?

        Also why aren't the downpipes showing gains even once tuned?
      1. SpeedLimit?'s Avatar
        SpeedLimit? -
        Terry@BMS, what's the downtime for switching downpipes on that motor?
      1. Sticky's Avatar
        Sticky -
        @Terry@BMS
      1. blkclk550's Avatar
        blkclk550 -
        Click here to enlarge Originally Posted by SpeedLimit? Click here to enlarge
        Terry, what's the downtime for switching downpipes on that motor?
        3-4 hours i had mine done
      1. Terry@BMS's Avatar
        Terry@BMS -
        Click here to enlarge Originally Posted by SpeedLimit? Click here to enlarge
        Terry@BMS, what's the downtime for switching downpipes on that motor?
        I've not done the job myself so I really have no idea. I imagine a good 3-4hrs of labor though.
      1. SpeedLimit?'s Avatar
        SpeedLimit? -
        Click here to enlarge Originally Posted by blkclk550 Click here to enlarge
        3-4 hours i had mine done
        Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
        I've not done the job myself so I really have no idea. I imagine a good 3-4hrs of labor though.
        Thanks guys
      1. 330i ZHP's Avatar
        330i ZHP -
        does any of this happen to the S63? I have the AR catted DPs and ESS tune
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 330i ZHP Click here to enlarge
        does any of this happen to the S63? I have the AR catted DPs and ESS tune
        The S63 pushes much higher boost targets so the downpipes seem to be a much higher point of restriction.
      1. 330i ZHP's Avatar
        330i ZHP -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        The S63 pushes much higher boost targets so the downpipes seem to be a much higher point of restriction.
        Does that mean, YES, the DPs are causing a restriction?
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 330i ZHP Click here to enlarge
        Does that mean, YES, the DPs are causing a restriction?
        Yes. Did you see this?

        http://www.bimmerboost.com/content.p...r-on-a-Dynojet