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    Question N54 Short Shift - Myth?

    Hi Folks,

    I hear pretty frequently about people who short shift the N54 because it runs out of steam at the higher RPMs and the power band drops off. When you look at a dyno, I can totally understand why you might think short shifting would get you faster times. But what really matters is the power that makes it to the ground and I think we might be forgetting about the multiplicative impact of gearing.

    I pulled a stock dyno graph from Automobile magazines N54 dyno and plotted that by each gear (manual transmission with a 3.08 final drive). If you really were better off short shifting, you would expect to see a higher gear produce more power at the wheels than a lower gear (e.g. 4th gear putting more power to the ground than 3rd gear at higher RPMs). But this isn't the case when you figure in the multiplication of the gearing.

    Click here to enlarge

    You could potentially argue that there may be a point between 6500RPMs and 7000RPMs in 4th that it may make sense to shift to 5th (depending on where the RPMs fall when you shift), and same for 5th to 6th, but I think the differences are probably so minor that they aren't worth the effort.

    What do you all think - am I off in the weeds? Or are we all losing time by short shifting?

    -Rich

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    From my own personal experience, short shifting instead of shifting at redline has got me better ET and Trap speeds in the 1/4 mile.

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    Now, redo the math for torque instead of HP and you'll see why you'd want to short shift Click here to enlarge
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    Click here to enlarge Originally Posted by marv85 Click here to enlarge
    Now, redo the math for torque instead of HP and you'll see why you'd want to short shift Click here to enlarge
    not entirely how it works

    horsepower is simply torque over time, hence you can have more power but less torque in higher RPM's.. jjust because per stroke you're making say, figures out of my ass here.. 30% less torque.. you're still making only 10% less power, so torque-over-time loss is not so bad.

    more horsepower is more acceleration in simple terms

    basically: no, you want to keep 'average' power (area under the curve) as high as possible, regardless of torque production

    otherwise.. basically any motor that doesn't have a flat torque 'curve' you'd be better off shifting waaay before peak power, which is silly.


    anyone with a graphics calculator or who knows how to use matlab could work it out in 2 minutes, plot the graph with enough datapoints (pretty easy to roughly get eyeballing), work out the RPM drop from say 3rd to 4th, 2nd to 3rd, whatever.. and put in an equation to work out the XXXX range that has the most area under the curve.. after doing so from gear to gear you'd know the EXACT optimum shift point.. and it could be done for any gear

    whoever does it would be guaranteed some +ve reps... i'd give it a go but i am le tired haha Click here to enlarge

    ED: another way of looking at it is gear1 torque = gear2 torque after RPM drop.. if you want to put it into torque terms lol
    Last edited by Flinchy; 03-12-2013 at 04:35 AM.

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    http://www.welltall.com/ymc/discovery/car/shiftpt.html formulas on this page handy for anyone keen enough to do it

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    Click here to enlarge Originally Posted by richpike Click here to enlarge
    I think we might be forgetting about the multiplicative impact of gearing.
    Most of these people just look at dyno number and pay 0 attention to gearing. The same people who think the M3 has no torque when it has far more gearing multiplication.

    At least someone is exploring this, props.


    People need to understand they have way more torque in 1st, 2nd, 3rd, etc. and shorter gearing probably will hurt. You need to plot out the torque by MPH.

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    http://www.welltall.com/ymc/discovery/car/shiftpt.html formulas on this page handy for anyone keen enough to do it
    Now we are talking. I'll take a look tonight.

    -Rich

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    not entirely how it works

    horsepower is simply torque over time, hence you can have more power but less torque in higher RPM's.. jjust because per stroke you're making say, figures out of my ass here.. 30% less torque.. you're still making only 10% less power, so torque-over-time loss is not so bad.

    more horsepower is more acceleration in simple terms

    basically: no, you want to keep 'average' power (area under the curve) as high as possible, regardless of torque production

    otherwise.. basically any motor that doesn't have a flat torque 'curve' you'd be better off shifting waaay before peak power, which is silly.


    anyone with a graphics calculator or who knows how to use matlab could work it out in 2 minutes, plot the graph with enough datapoints (pretty easy to roughly get eyeballing), work out the RPM drop from say 3rd to 4th, 2nd to 3rd, whatever.. and put in an equation to work out the XXXX range that has the most area under the curve.. after doing so from gear to gear you'd know the EXACT optimum shift point.. and it could be done for any gear

    whoever does it would be guaranteed some +ve reps... i'd give it a go but i am le tired haha Click here to enlarge

    ED: another way of looking at it is gear1 torque = gear2 torque after RPM drop.. if you want to put it into torque terms lol

    Totally get what you're saying... my whole point was your ED. Once you're at the point where the next gear's torque and present gear's torque intersect (and the TQnext is about to be > TQpresent) then you're better off shifting, especially on our cars with stock turbos where midrange is where the car shines
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    Is this based on the stock power band? You would definitely want to run out the gears if your car is stock, I believe that when you are tuned on stock turbo's is when it makes better sense to short shift, how do the numbers look there? I know they are really peaky in the mid range and drop substantially up top.

    Also, there is higher drivetrain loss associated with higher gearing I believe (although usually people say it's made up for by the gearing advantage). Although that could just be based on numbers read on a dynojet and not apply to real life, I'm uncertain there.

    Good topic to keep in mind though. Gearing plays a big role in a race.

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    Click here to enlarge Originally Posted by V8Bait Click here to enlarge
    Also, there is higher drivetrain loss associated with higher gearing I believe (although usually people say it's made up for by the gearing advantage). Although that could just be based on numbers read on a dynojet and not apply to real life, I'm uncertain there.
    The drivetrain loss doesn't change just the numbers change depending on the gear on the dynojet.

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    Click here to enlarge Originally Posted by zeel Click here to enlarge
    From my own personal experience, short shifting instead of shifting at redline has got me better ET and Trap speeds in the 1/4 mile.
    I've also experienced a faster ET and Trap from shifting at 6100, as @dzenno@ProTUNING Freaks had instructed me.
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    Click here to enlarge Originally Posted by V8Bait Click here to enlarge
    Is this based on the stock power band? You would definitely want to run out the gears if your car is stock, I believe that when you are tuned on stock turbo's is when it makes better sense to short shift, how do the numbers look there? I know they are really peaky in the mid range and drop substantially up top.

    Also, there is higher drivetrain loss associated with higher gearing I believe (although usually people say it's made up for by the gearing advantage). Although that could just be based on numbers read on a dynojet and not apply to real life, I'm uncertain there.

    Good topic to keep in mind though. Gearing plays a big role in a race.
    Good insights. Right now it is based on a stock powerband. But I was already thinking down your path and actually started to graph out Dzenno's record run since it has a monstrous midrange. I'll roll that in to my second analysis based on the website from Flinchy above.

    -Rich

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    Faster times @ 6250 for me. Besides the math you need to see also the acceleration rate curve. How long does it take to go from 6K to 7K? As the rate of acceleration falls off is it a net gain or loss to stay with it to 7K+?
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    Click here to enlarge Originally Posted by BEAR-AvHistory Click here to enlarge
    Faster times @ 6250 for me. Besides the math you need to see also the acceleration rate curve. How long does it take to go from 6K to 7K? As the rate of acceleration falls off is it a net gain or loss to stay with it to 7K+?
    What were your times?

    I personally saw no difference if I shifted at 6k or let the trans shift itself at 6800rpms. If I shifted early, I would flatline and if I didn't shift early, I wouldn't flatline...

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    Click here to enlarge Originally Posted by marv85 Click here to enlarge
    Totally get what you're saying... my whole point was your ED. Once you're at the point where the next gear's torque and present gear's torque intersect (and the TQnext is about to be > TQpresent) then you're better off shifting, especially on our cars with stock turbos where midrange is where the car shines
    Yeah but since tq directly relates to power, ... Say you tq peaks then SLOWLY+ steadily drops, but makes power to redline, redline would still be the best shift point even if best torque curve is way back..

    I know thats not what we're talking about really, but worth mentioning

    For stock frame n54's, no arguing that redline is WAY off powerband though

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    Click here to enlarge Originally Posted by Flinchy Click here to enlarge
    Yeah but since tq directly relates to power, ... Say you tq peaks then SLOWLY+ steadily drops, but makes power to redline, redline would still be the best shift point even if best torque curve is way back..

    I know thats not what we're talking about really, but worth mentioning

    For stock frame n54's, no arguing that redline is WAY off powerband though
    Exactly, and what we're both saying here that shifting before redline is benefical on our car especially when they're tuned but it's a general rule. It definitely correlates directly to how the powerband looks like.

    In my case, I got the fastest performance when shifting around 6200
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    Gear doesn't effect the measured numbers but can effect power loss through the drivetrain and higher loads will result on more power.


    When evaluating shift points all you need is HP and useable rpm range. A tuned n54 you may actually have a choice due to the bell like HP curve to rev it out or short shift... depends on the tuning of course. If HP and torque have similar maxes, maybe best to rev it out. Torque considerably higher, short shifting prob better.

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    Gear doesn't effect the measured numbers but can effect power loss through the drivetrain and higher loads will result on more power.
    How is it changing drivetrain loss when it is actually changing torque multiplication? Drivetrain loss changes from one RPM point to the next anyway and the 15% standard was invented by the dynojet. Forget drivetrain loss that isn't what is changing the numbers when you change gearing.

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    We've discussed this before. Math is the same... higher gear you have more mph + less acceleration = same HP. Lower gear more accel + lower mph. The rate of work is the same.

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    Math is the same... higher gear you have more mph + less acceleration = same HP. Lower gear more accel + lower mph. The rate of work is the same.
    What? The math is not the same. Any gearing change changes the math significantly not sure what you are talking about.

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    LEMANS BLUE M-TECH E92->PROCEDE REV3::ETS 7" FMIC::RACELAND DPS::WAVETRAC DIFF::DEFIV DIFF LOCKDOWN::DEFIV OCC::DEFIV INTAKE::RB PCV

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    Click here to enlarge Originally Posted by JoshBoody Click here to enlarge
    We've discussed this before. Math is the same... higher gear you have more mph + less acceleration = same HP. Lower gear more accel + lower mph. The rate of work is the same.
    Right. The rate of WORK (force of the crank * distance/circumference of flywheel) - not the amount of POWER (work / time). Two separate things. Shifting at torque peak of engine is nearly never advantageous.

    http://www.allpar.com/eek/hp-vs-torque.html

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    theories and ricer math Vs proven tried and true facts

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    Click here to enlarge Originally Posted by inlineS54B32 Click here to enlarge
    Right. The rate of WORK (force of the crank * distance/circumference of flywheel) - not the amount of POWER (work / time). Two separate things. Shifting at torque peak of engine is nearly never advantageous.

    http://www.allpar.com/eek/hp-vs-torque.html
    In other words - same amount of work is done going from 0-100 starting in 5th gear (if possible) as starting in 1st and rowing through gears. The amount of force to the wheels, however - is much higher in 1st/2nd/etc. - so average power used is MUCH higher.

    Running a car at or near the engines maximum power is always best, as maximum torque to the wheels in each non-overdriven gear is generated at maximum engine power, not torque. It's clearly simple to understand when reading his page, or thinking of a diesel creating tons of torque down low.

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