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    • How to inflate dyno numbers on a Dynojet - 24 wheel horsepower change on a tuned F13 M6 S63TU from 4th to 5th gear

      We argue about dyno numbers here. A lot. Maybe a bit too much. Now, dyno's are incredibly useful. Not just for car owners to see the difference modifications make but for tuners as well. There are many different dynamometers out there but the Dynojet is arguably the most popular. Why? Because it is peak number friendly and the software and graphs are very well done. Just look at the numbers this BMS tuned M6 is putting down at over 660 horsepower to the rear wheels.

      Impressive right? Absolutely. But then you look at the blue line on the graph and realize it is a 5th gear dyno. The red line is a 4th gear dyno and the numbers drop to to 638 wheel horsepower. Torque also takes a tumble from 636 lb-ft to 602 lb-ft.

      What causes this? The fact that the Dynojet is an inertia based dyno. This means a fixed weight is spun and how quickly it is spun is measured. The computer plugs the values into an equation and spits out a graph with numbers. Now did the car suddenly gain horsepower because it changed gears? No.

      What happened is that the drum was spun faster in 5th gear than in 4th gear. This graph illustrates the effect perfectly as it is set to read in MPH. Notice the higher MPH has the higher numbers because it is spinning more quickly. If this graph was reading RPM and not MPH someone without morals could claim a horsepower gain saying they made some tuning or modification changes when really all that changed was the gear that the dyno run took place in.

      This does not make the Dynojet an invalid tool. Due to the amount of runs out there and its popularity it is an incredibly important and useful tool. However, it is important to understand context and that numbers are not set in stone. There are many variables that affect them. Why we like to see timeslips in addition to dyno graphs to get a complete picture is because you can not do a 1/4 mile pass in this car solely in one gear. Well, you can, but you will not like the result. You have to go through the gears in progression to get an accurate representation on the drag strip you can not simply just say I'm doing this 1/4 mile sprint in 6th gear to get the quickest and fastest possible time.

      If a tuner will not provide a run file for download to analyze or only does runs in a higher gear, question it. Tuners who have nothing to hide will show their runs. Also, if you get a baseline dyno and then get some modifications, dyno afterwards to see the difference in that same gear to minimize variables.

      No automotive performance numbers are set in stone. No single measurement is perfect. The more data from various sources for analysis, the more light is shed on the big picture.


      This article was originally published in forum thread: How to inflate dyno numbers on a Dynojet - 24 wheel horsepower change on a tuned F13 M6 S63TU from 4th to 5th gear started by Sticky View original post
      Comments 16 Comments
      1. 5soko's Avatar
        5soko -
        About to make a $100 intake, sell it for $500 and do this, show everyone it gains 24WHP and watch my money stack..
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 5soko Click here to enlarge
        About to make a $100 intake, sell it for $500 and do this, show everyone it gains 24WHP and watch my money stack..
        How many people make a living doing this? More than people realize.
      1. 5soko's Avatar
        5soko -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        How many people make a living doing this? More than people realize.
        10000%... Exhaust, intakes, pulley, and some tuners... Im sure they all take advantage of all these small 'adjustments' and tricks to show gains.. Hey, if no1 asks, they arent look as shady from their standpoint. Good to spread this type of knowledge..
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 5soko Click here to enlarge
        10000%... Exhaust, intakes, pulley, and some tuners... Im sure they all take advantage of all these small 'adjustments' and tricks to show gains.. Hey, if no1 asks, they arent look as shady from their standpoint. Good to spread this type of knowledge..
        It's why I always prefer independent results. I always like to see a graph but if users can't replicate what a tuner posted then...
      1. George Smooth's Avatar
        George Smooth -
        There is a torque limitation when dynoing in 4th vs 5th on a V8TT so this is not the best example of a graph.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by George Smooth Click here to enlarge
        There is a torque limitation when dynoing in 4th vs 5th on a V8TT so this is not the best example of a graph.
        Well maybe not the best example but the point still stands about using higher gears for higher numbers and how the numbers can change based on the gear.
      1. NikB316's Avatar
        NikB316 -
        Easy trick and I'm sure companies are using it. Should always compare apples to apples but that doesn't always happen. When we were dynoing my car at Undercover I asked Garth (owner) which gear most accurately represents the car's power given the difference in 4th & 5th. He told me to google some ratio I forget what it's called. Was able to determine that in the M5/6 5th is the most accurate representation. Just sucks that there's no way to remove this speed limiter. Can't get a full graph in 5th.

        Someone know the name of the ratio I'm talking about? Slipped my mind.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by NikB316 Click here to enlarge
        Easy trick and I'm sure companies are using it. Should always compare apples to apples but that doesn't always happen. When we were dynoing my car at Undercover I asked Garth (owner) which gear most accurately represents the car's power given the difference in 4th & 5th. He told me to google some ratio I forget what it's called. Was able to determine that in the M5/6 5th is the most accurate representation. Just sucks that there's no way to remove this speed limiter. Can't get a full graph in 5th.

        Someone know the name of the ratio I'm talking about? Slipped my mind.
        The ratio you're looking for is 1:1.
      1. rooringhusky's Avatar
        rooringhusky -
        Click here to enlarge Originally Posted by NikB316 Click here to enlarge
        Easy trick and I'm sure companies are using it. Should always compare apples to apples but that doesn't always happen. When we were dynoing my car at Undercover I asked Garth (owner) which gear most accurately represents the car's power given the difference in 4th & 5th. He told me to google some ratio I forget what it's called. Was able to determine that in the M5/6 5th is the most accurate representation. Just sucks that there's no way to remove this speed limiter. Can't get a full graph in 5th.

        Someone know the name of the ratio I'm talking about? Slipped my mind.
        The answer to your question, its called the transmission gear ratios...And as Sticky said above the one your looking for when dynoing for comparison purposes or to be most precise is the gear closest to 1:1...Sucks by the way that the M5/M6 hit speed limiter issues in 5th
      1. Terry@BMS's Avatar
        Terry@BMS -
        I don't think any legitimate tuner or parts manufacturer would try to compare dyno runs done in different gears. If you ever suspect they are doing that just request the plot by road speed. Click here to enlarge

        PS. If you want to see "power" drop like a rock do the run in 3rd gear!
      1. m6beast's Avatar
        m6beast -
        This is my car and these two dyno runs we're to show a power gain between two gears, not showing a modification for gained performance. Also the 1:1 gear for this car is 6th, but do to the topend limiter power will be cut too early.

        Also these two runs in the gears were for a base before installing my meth kit, once the car is running for at least a 1000 miles with meth I will dyno both gears again to see what actual power gains in 4th and 5th

        Also in fifth the car stopped pulling at 6200 rpm do to topend limiter.
        If you read my origimal post correctly you would know this was to show 4th and 5th gear comparisons as you can see on the dyno graph shows time and day.
        Hope your post gives true detail to my dyno runs. Also Once I get the topend limiter off the car, then I will be ready to show more accurate numbers to redline.
        hope fellow members get the right facts thanks and take care.
        G
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by m6beast Click here to enlarge
        If you read my origimal post correctly you would know this was to show 4th and 5th gear comparisons as you can see on the dyno graph shows time and day.
        My article has nothing to do with what you wanted to show. I used the run to illustrate my point about how changing gears on a dynojet can sway stated peak output significantly.

        Click here to enlarge Originally Posted by m6beast Click here to enlarge
        hope fellow members get the right facts thanks and take care.
        I have no idea what you are taking issue with as this isn't about you or designed around you in any way. Whatever 'facts' you are talking about are irrelevant. But here's a positive rep in the spirit of friendship despite your attitude.
      1. m6beast's Avatar
        m6beast -
        Lol! Are you serious?! My intention wasn't to to flame your boat lol. Just stating my dyno numbers do to gears and my intention, incase fellow members took your post the wrong.
        No worries and don't be so defensive as for me it looks like you're the one with the attitude. Hope you have a better day.
        Take care
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by m6beast Click here to enlarge
        Lol! Are you serious?! My intention wasn't to to flame your boat lol. Just stating my dyno numbers do to gears and my intention, incase fellow members took your post the wrong.
        No worries and don't be so defensive as for me it looks like you're the one with the attitude. Hope you have a better day.
        Take care
        Nobody thought you were trying to manipulate numbers. Your name isn't even mentioned. You took some kind of perceived offense that isn't there. If me saying let's be positive is me being defensive then I think the issue is in your own head.
      1. m6beast's Avatar
        m6beast -
        Wow! thought those were stories about you, I guess not....... Anyway thanks for the enlightment keep the posts coming I've enjoyed them through the years.
        take care man
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by m6beast Click here to enlarge
        Wow! thought those were stories about you, I guess not....... Anyway thanks for the enlightment keep the posts coming I've enjoyed them through the years.
        take care man
        Sounds good.