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Dyno tests confirm Nissan GT-R drivetrain loss, power ratings

 

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Testing cars for power ratings is a tough and tricky business - accounting for different conditions, locations, equipment and techniques can make it tough to generalize results. And to make matters worse, there is often a lot of guesswork employed to get between real, delivered wheel horsepower and output at the crankshaft, or vice-versa. A recent test of Nissan's GT-R has answered some of the ongoing questions of how it performs so well, however, and taken a good bit of the fiction out of the process.

Rumors and reports from around the web have been claiming Nissan's stated figures for the GT-R's twin-turbo V6 are understated ever since it began its remarkable climb up the many performance charts. All-wheel drive and tons of rubber just couldn't make up for the massive power deficit, they claimed. But it turns out Nissan's claimed 473hp (353kW) figure isn't far from the truth at all, according to MotorTrend. The torque numbers are about 40lb-ft (54Nm), or roughly 9%, larger than Nissan's 434lb-ft (588Nm) rating, and could help explain a little of the car's low-end acceleration abilities.

The key to this latest round of testing is the use of Hyper Power Dynamometer's DYNOmite, which allows testing not just of engine output, but of powertrain drag. After a dyno pull, instead of ceasing to record data, the machine records the slow-down period, and measures the drag due to the car's powertrain, including engine, transmission and wheels.

The end result? As physics would suggest, the parasitic losses of the drivetrain increase with speed, varying from 23hp (17kW) at 50mph to 84hp (62kW) at 100mph. That works out to a real-world inefficiency ranging between 5-17%, depending on speed - quite good for an AWD car.

One thing to keep in mind, however, is that this is just one particular example of the car - power figures can and will vary from vehicle to vehicle. It will simply take time and repetition to see if these results are more or less representative of the general population of Nissan GT-Rs than previous tests. The method, however, is a definite improvement.

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Comments (8)
  1. Meh, this dyno stuff is all a bunch of hooey anyway. All that really matters is real-world head-to-head tests, and the GT-R does just fine there.
     
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  2. Transmission 'inertia' has nothing to do with transmission inefficiency. Inertia is only relavant on an inetial dyno as opposed to a real dyno that measure steady state torque output. An inertial dyno can only calculate power by timing how long it takes to accelerate a 'known' mass, usually an acuratley calibrated flywheel. This is a peak power test and has nothing to do with constant torque output (ie horsepower is usually only ever 'calculated' by torque x rpm / 5252 = HP)

    The largest factor of mechanical transmission loss is gear inefficiency. Every type of gear is rated at a % loss at the teeth face of between 10-30%. These losses are an engineering fact. Each gear in the transmission between the flywheel and the tires that power has to transmit through ad up to a total loss of closer to 30-40%.
     
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  3. Transmission 'inertia' has nothing to do with transmission inefficiency. Inertia is only relavant on an inetial dyno as opposed to a real dyno that measure steady state torque output. An inertial dyno can only calculate power by timing how long it takes to accelerate a 'known' mass, usually an acuratley calibrated flywheel. This is a peak power test and has nothing to do with constant torque output (ie horsepower is usually only ever 'calculated' by torque x rpm / 5252 = HP)

    The largest factor of mechanical transmission loss is gear inefficiency. Every type of gear is rated at a % loss at the teeth face of between 10-30%. These losses are an engineering fact. Each gear in the transmission between the flywheel and the tires that power has to transmit through ad up to a total loss of closer to 30-40%.

    DUDE wheer are you getting this 'inertia' thing from? The article doesn't even mention it...

    And you can quote all the textbook theory you want, but this is about an actual test on equipment used to measure these things
     
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  4. "DUDE wheer are you getting this 'inertia' thing from? The article doesn't even mention it..."

    You have no idea pal!

    Read the text: "After a dyno pull, instead of ceasing to record data, the machine records the slow-down period, and measures the drag due to the car's powertrain, including engine, transmission and wheels"

    Did you comprehend any of that? That "drag" is is the SUBJECT the article is about and that actually refers to measuring drive train "inertia".

    You should probably have a quick recap of some basic high school science and learn how to spell.
     
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  5. "DUDE wheer are you getting this 'inertia' thing from? The article doesn't even mention it..."

    You have no idea pal!

    Read the text: "After a dyno pull, instead of ceasing to record data, the machine records the slow-down period, and measures the drag due to the car's powertrain, including engine, transmission and wheels"

    Did you comprehend any of that? That "drag" is is the SUBJECT the article is about and that actually refers to measuring drive train "inertia".

    You should probably have a quick recap of some basic high school science and learn how to spell.

    hahahha nice. tell a guy to get a primer on physics then equate drag to inertia. maybe you should take your own advice.

    1) drag is aerodynamic, 2) friction is what is actually being referred to, but 'drag' is a colloquial way to say it, so that's excusable, 3) inertia refers to to the tendency of a body in motion to remain in motion, and relates to the force imparted upon a mass. friction (or 'drag' in the colloquial sense) works in OPPOSITION to inertia; inertia is assumed, and is determinate by the mass of the objects in motion and the forces imparted thereto. No need to measure on a dyno - once you know the RPM, you can calculate that with a scale and sheet of paper.

    What is being measured is the friction (which is dependent upon any number of factors, including materials, surface condition, lubrication, surface area in contact), and can be relative to speed, force and other factors. Hence the measurements.
     
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  6. twinturboz. you couldnt have put it more nicely
    "What is being measured is the friction (which is dependent upon any number of factors, including materials, surface condition, lubrication, surface area in contact), and can be relative to speed, force and other factors. Hence the measurements."
    by twinturboz #5, Posted: 1/9/2009
    you can see where is education stops, as you go further into physics unversity level up wards you learn things that the average lay man cannot comprehend because his knowledge has stopped growing and a 5-17% drive train loss is remarkable for a car in fact its almonst insane when you think about is that its a awd car too with so much more drive train parts.
     
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  7. Guys, it's really simple, unless I'm misunderstanding something.
    The dyno is measuring how long the drivetrain takes to stop spinning after you stop applying throttle. The more friction, the faster it spins down. The role of the drivetrain mass is that the more mass there is, the longer it takes to spin down. I assume they know the mass so they can adjust for that.
     
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  8. Hello,I run my own business and we have a 4WD Dyno.I haven't heard of Drive train losses being calculated from deceleration post power run. the issues i have:
    1:Gears running in deceleration run on the back,gears are cut differently unless your talking about straight cut gears.
    2:I own a R32 Skyline MC-R (OK re-badged and modified I.E RB30DET 350kw@all 4 wheels)full power the toque to the front wheels is about 50/50 split back off & it's rear drive,this would change the readings alot.
    3: under full load at higher RPM there will be greater losses, low torque from dyno roller inertia going back through the drive train would be very hard to calculate correctly, clutch in or out?

    Transmission dyno Google it, then add your thoughts yours Geoff
     
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