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  1. #1
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    Which Gears Deliver the Most Boost?

    Greetings friends,

    I've owned my '07 335i E92 for almost six years yet I still relish all the learning that is available out there especially in a forum like this regarding the N54 engine.

    Can anyone tell me how much boost is produced throughout the gearing pattern? More specifically, what percent boost is produced in what gears? My indie once commented: "Second is where you get your boost.". Does this mean most of boost is concentrated in 2nd? Also, I can feel and hear when the turbos kick in but is there an RPM number that matches boost by gear? Are there aftermarket display gauges that provide this kind of feedback? Not sure if I'm asking the right questions, just trying to understand the true potential of this engine.

    Thank you!

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    6 out of 6 members liked this post. Yes Reputation No
    Click here to enlarge Originally Posted by Love2xlr8 Click here to enlarge
    Greetings friends,

    I've owned my '07 335i E92 for almost six years yet I still relish all the learning that is available out there especially in a forum like this regarding the N54 engine.

    Can anyone tell me how much boost is produced throughout the gearing pattern? More specifically, what percent boost is produced in what gears? My indie once commented: "Second is where you get your boost.". Does this mean most of boost is concentrated in 2nd? Also, I can feel and hear when the turbos kick in but is there an RPM number that matches boost by gear? Are there aftermarket display gauges that provide this kind of feedback? Not sure if I'm asking the right questions, just trying to understand the true potential of this engine.

    Thank you!

    Hello, boost is a function of engine load. Ideally, if the turbos had no rotational inertia, they would spool up instantly and you would see the same boost in all gears. Because 1st gear is very short and the engine is loaded the least in first gear, a lot of times the engine will 'run away' from the turbos, that is actually get to redline faster than the turbos can spool up. There is no magic gear that makes the most boost, the turbos are designed to make and hold a certain amount of boost vs engine load, where you get that engine load depends on a lot of factors gearing being only one factor. I dont know who told you that second gear is where you get your boost, that doesnt make sense, you get boost in all gears. Generally, the higher the gear the earlier your boost will come on because the engine stays loaded longer throughout the RPM band and RPM changes are slower the higher gear you are in.
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Hello, boost is a function of engine load. Ideally, if the turbos had no rotational inertia, they would spool up instantly and you would see the same boost in all gears. Because 1st gear is very short and the engine is loaded the least in first gear, a lot of times the engine will 'run away' from the turbos, that is actually get to redline faster than the turbos can spool up. There is no magic gear that makes the most boost, the turbos are designed to make and hold a certain amount of boost vs engine load, where you get that engine load depends on a lot of factors gearing being only one factor. I dont know who told you that second gear is where you get your boost, that doesnt make sense, you get boost in all gears. Generally, the higher the gear the earlier your boost will come on because the engine stays loaded longer throughout the RPM band and RPM changes are slower the higher gear you are in.
    Wow! What a great explanation, thanks. Seems to make perfect sense when you consider the laws of physics. With regard to rotational inertia, this must be the same reason factory horsepower(at the flywheel) is greater than wheel horsepower?

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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Hello, boost is a function of engine load. Ideally, if the turbos had no rotational inertia, they would spool up instantly and you would see the same boost in all gears. Because 1st gear is very short and the engine is loaded the least in first gear, a lot of times the engine will 'run away' from the turbos, that is actually get to redline faster than the turbos can spool up. There is no magic gear that makes the most boost, the turbos are designed to make and hold a certain amount of boost vs engine load, where you get that engine load depends on a lot of factors gearing being only one factor. I dont know who told you that second gear is where you get your boost, that doesnt make sense, you get boost in all gears. Generally, the higher the gear the earlier your boost will come on because the engine stays loaded longer throughout the RPM band and RPM changes are slower the higher gear you are in.
    +rep, great explanation

    I do see where a lot of people think 2nd gear is the "boost gear." 2nd feels like a good balance of load and RPM ramp up rate.
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    For what its worth Terry advised me to make a dyno pull in 5th on the 7DCT to get the max WHP hero reading. Turbos will have the most time to fully build boost in this gear. That equates to IIRC about 135mph. Right now I am at about 380whp in 3rd gear on a Dynojet. Happy with the number since I only have a JB4 & 5” FMIC running 5gal of 100 in a tank full of 93.
    Kevin
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    OP, I believe you would be well served to learn to read datalogs and follow the boost traces and that will give you a good idea on how boost functions.
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    I think on certain FWD platforms, with a boost controller or a standalone engine management system, you can target boost in each gear to help control torque steer. Maybe that's where the theory spilled over from, but it totally does not apply to our load targeting DME.
    [02/07 E92 335i 6MT] - Under Construction

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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
    OP, I believe you would be well served to learn to read datalogs and follow the boost traces and that will give you a good idea on how boost functions.
    Thanks. Will do. Geez, is there a school for this? LOL!

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    Click here to enlarge Originally Posted by nitehawk Click here to enlarge
    I think on certain FWD platforms, with a boost controller or a standalone engine management system, you can target boost in each gear to help control torque steer. Maybe that's where the theory spilled over from, but it totally does not apply to our load targeting DME.
    I think your correct. but not just fwd cars, its just about every other turbo car that wants to maximize traction and capable of pushing big boost

  10. #10
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    Click here to enlarge Originally Posted by nitehawk Click here to enlarge
    I think on certain FWD platforms, with a boost controller or a standalone engine management system, you can target boost in each gear to help control torque steer. Maybe that's where the theory spilled over from, but it totally does not apply to our load targeting DME.
    If you're ever In a 400+whp civic(or just about any FWD car) you'll see that boost per gear and a progressive boost controller are necessary to not only put the power down but to keep from killing yourself lol

    Same goes for BIG HP RWDs.
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  11. #11
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    Op i think you should get a boost gauge and do some logs, are you tuned?
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    Click here to enlarge Originally Posted by rader1 Click here to enlarge
    OP, I believe you would be well served to learn to read datalogs and follow the boost traces and that will give you a good idea on how boost functions.
    The best way to learn about how boost changes with engine load is to look at logs all day every day for months straight. He will start to get a feel for what kind of response the turbos will have given certain conditions. Change things up, that way you know what variables do what. For instance, you will see that on a stock car to hit 17 psi takes longer (albiet still a very short amount of time like 1 second or so) than a car with catless downpipes and and intake and chargepipe.

    Restrictions in the system as a whole, only add to the way the turbos RESPOND to CHANGES in engine load. More restrictions = either takes longer for the turbos to respond or you just will never hit the target boost becaues of huge pressure drops. Digressing though....
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  13. #13
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    Click here to enlarge Originally Posted by bobS Click here to enlarge
    Op i think you should get a boost gauge and do some logs, are you tuned?
    Yes, I have Dinan S2 but I'm seriously looking at other set-ups you guys have recommended like JB4 and Cobb. I bought into Dinan at a time when I was relatively unaware of other tunes plus their warranty was appealing. However, now that I'm out of warranty I am completely open to other options. JB4 and Cobb look like they have several selectable driving options that are not available with my Dinan S2 for a lot less $$$. I live close to the Burger shop so my inclination is to go in there to further my education, possibly meet Terry and get it installed. I am really hoping to notice a difference between Dinan and JB4.

  14. #14
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    You'll be pissed you wasted money and time with the Dinan, the jb4 or Cobb will feel way more powerful
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