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Thread: Transmission losses

  1. #1
    Regular Member Hideous's Avatar
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    Default Transmission losses

    was just reading this article, quite good
    http://www.pumaracing.co.uk/POWER3.htm

    i'd prefer to stay on the "conservative" side of things - you can never know what the actual transmission losses are without taking the engine out, but the 20-30% that some RRs tell you (for FWD) seems highly optimistic, imo.

    15% TL is the best guess, imo.

    In a way, this flywheel power guess is kind of irrelevant anyway, once you've got your "at the road wheels" power figure that's all you need to know. High output at the wheel is what wins races, not some dodgy flywheel conversion.

  2. #2
    Full Member GazVXLINE170's Avatar
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    Vehicle : Insignia

    Trim : SRI VX-Line Nav

    Engine : 2.0 CDTI [170 PS]

    Year : 2015

    Mileage : 27000

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    Funny how efficiency is great when measuring at the wheels and not so great when measuring at the flywheel. Typical efficiency of a gearbox is 82-85%. That's three times that of the engine, which uses 27% of the power it produces - to move the car.

    Gazza4
    Insignia VX-Line Nav CDTI 170.

  3. #3
    Regular Member john_k_sri's Avatar
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    Vehicle : Vectra

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    Default

    How come the 'drag' figure is shown on a power graph, which when added to the figure at the wheels and a minor correction (for air temperature/humidity?) gives you the power bhp figure, or are RR operators simply using a pre-set percentage loss figure?

    I just wonder how 'drag' is measured on the rollers.

  4. #4
    Full Member GazVXLINE170's Avatar
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    Default

    Not all rr do this so some base it on the 20% which tbh isn't unreal.

    Quote Originally Posted by john_k_sri View Post
    How come the 'drag' figure is shown on a power graph, which when added to the figure at the wheels and a minor correction (for air temperature/humidity?) gives you the power bhp figure, or are RR operators simply using a pre-set percentage loss figure?

    I just wonder how 'drag' is measured on the rollers.
    They let the transmission and wheels decelerate from speed then multiplied with the moment-of-inertia (rotational equivalent of mass) of transamission shaft - gives the drag torque.

    The only way to get true power reading off of the engine is to remove the engine and hook the flywheel up to a dyno.

    Gazza4
    Insignia VX-Line Nav CDTI 170.

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    Regular Member Hideous's Avatar
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    Quote Originally Posted by john_k_sri View Post
    How come the 'drag' figure is shown on a power graph, which when added to the figure at the wheels and a minor correction (for air temperature/humidity?) gives you the power bhp figure, or are RR operators simply using a pre-set percentage loss figure?

    I just wonder how 'drag' is measured on the rollers.
    this is another good article http://www.sdsefi.com/techdyno.htm
    quote "On an inertial chassis dyno, it is virtually impossible to calculate the the moment of inertia of every tire, wheel, gear, joint , axle and shaft in the power train between the crankshaft and roller, therefore its results cannot offer an accurate HP figure. Even with coastdown drag measurements, these cannot be accurately calculated as different factors are affected in different ways. Some are proportional, some are inverse squared functions etc. Inertial engine dynos offer a very accurate figure if properly calibrated as only the flywheel's moment of inertia needs to be calculated and added to that of the billet. Water brake or eddy current dynos generally measure force (torque) directly through a ram or strain gauge so moments of inertia are not important on these in fully loaded tests."
    so basically, it can't be relied upon at all - until the engine is tested on its own.
    "The chassis dyno division of Bosch UK also suggest 15% as being a realistic estimate of transmission losses." - Not a bad bunch of people to listen to..

    So, until it can proven that the vectra-c actually loses 20%+ in the transmission, i'm sticking with 15%.

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    Full Member GazVXLINE170's Avatar
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    No one said it was acurate. Read my previous post. But you stick with 15% because after 10k it won't change but maybe after 60k it will a bit.

    I have also learned that if you want to fins something on the internet you'll find it. Most people use the engine hp as that give good clarification. If I followed the same argument as you then I would say don't measure torque in ft-lb's as that is technically wrong - Nm is the proper physical name for the quantity, but I don't, reason as that's not how 99.9999999% of the world works.

    Gazza45
    Last edited by GazVXLINE170; 15th April 2011 at 23:02.
    Insignia VX-Line Nav CDTI 170.

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    Default

    no worries -- i'd just rather the conservative estimate whenever there is considerable doubt. Seems to me there is a lot of doubt on this subject.
    IMO -- 20-28%(highest i've seen on here) TL is based on what these RR drag estimates churn out from the chassis dyno, and from what i've read - there are a lot of assumptions being made.

    still trying to learn more on this subject, maybe other vec-c users are thinking again about this too.
    wheel power is what matters - makes sense to ensure you get the actual wheel output result when you pay good money for a dyno test!
    Last edited by Hideous; 16th April 2011 at 00:29.

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    Full Member GazVXLINE170's Avatar
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    Year : 2015

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    Quote Originally Posted by Hideous View Post
    no worries -- i'd just rather the conservative estimate whenever there is considerable doubt. Seems to me there is a lot of doubt on this subject.
    IMO -- 20-28%(highest i've seen on here) TL is based on what these RR drag estimates churn out from the chassis dyno, and from what i've read - there are a lot of assumptions being made.

    still trying to learn more on this subject, maybe other vec-c users are thinking again about this too.
    wheel power is what matters - makes sense to ensure you get the actual wheel output result when you pay good money for a dyno test!
    I'm basing it on what I've seen at rr days and the losses measure find - 15-20% and tbh I haven't read differently on here - but that's not to say what you have read is incorrect.

    Gazza4
    Insignia VX-Line Nav CDTI 170.

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    Forum Moderator John LE's Avatar
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    TBH none of that matters, how it drives on the road is the important bit.

    Every RR works things out differently, some give good figures to get you to come back again, some give realistic figures and some give poor figures to get money out of you.

    The only real way is to take to the road and see if that re-map has changed how the car behaves.

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    Regular Member john_k_sri's Avatar
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    AS I have previously said BSR's stated post-remap bhp output figures seem to imply a loss of 15% based on my 3 rolling roads on my previous 2.0T, based on actual wheel hp figures.

    That would explain why their figures are often exceeded with an indicated drag figure of around 20%.

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