Mustang D

Totally agree Tuna, there is a huge amount of "assumed" crap relating to dyno readings. If the guy using the dyno doesn't understand how it works, how is he supposed to rely that to the customer. that's why Tractive Effort is displayed as most people don't know what it is so normally it is just accepted. (It's also a big number which people tend to like, and it takes no operator education) The main thing to look for on a graph that shows either Torque, Tractive Effort, Motive Force or Derived Torque is to gauge the minimum and maximum point and see how much difference there is between them, this shows how much torque you have across the entire rev range.

The conversion from Newtons to Newton Metres is such: Multiply the Newtons by 0.1085 and that will give you the Torque in NM. The figure of 0.1085 is the roller radius in metres, and this is what is used to calculate the Tractive Effort on DD Dyno's that have 217mm diameter rollers (99% of them). So for example, if you have 5500 newtons, this will be 596.75 Newton Metres at the rollers. If the dyno operator chooses to insert the correct kmh/rpm realationship, this 596.75nm figure would be reduced by the ratio of Engine Rpm to Roller Rpm to make the figure more user friendly, ie. you expect a torque loss at the wheels just like there is power loss, whereas in most cases there is a torque multiplication due to gearing. So if you had a vehicle that was making 256rwkw @ 100kph, this would be making 1000nm at the rollers (9216 newtons), is this bogus? If you were still making 1000nm @ 180kph, you would be then making 460rwkw, is this still bogus, a soft tune on a GenT1000 easily does that. If the correct kph/rpm was applied to the example of 1000nm at the rollers, it would be displayed as 769nm on a vehicle with 3.9 diff gears, done in a 1:1 gear ratio in the trans.

A colleague of mine fitted a fully programable Gas Vapour injection system to his T last weekend, the only drawback with it was the Injection nozzles only support 33KW per cylinder. His T normally runs 320RWKW, but is just installing the Gas for economy to drive it to and from his workshop, and these gas vapour systems are almost unoticable on switchover, so if he needs some grunt it is just a matter of pressing the switchover button to petrol. The end user price I think would be over 3K fitted.

Option 2 most definately.

This can be proven mathematically, and it does happen in practice. Nobody said that the ENGINE will have 7-8% more power, the fact is though, a lighter wheel/tyre combination with LESS INERTIA will produce higher figures on a Chassis Dyno. Look at what happens on a Dynpack Dyno, the numbers are significantly higher, because the wheels are removed altogether, less rotational Inertia means more power that it measured by the Dyno.

Different Tyre/Rim combinations definately effect RWKW readings, the reason is INERTIA. A 19" tyre/rim combination has more weight toward the outer circumference of the wheel, so the 19" tyre/wheel will consume more Torque to accelerate than a 17" tyre/wheel. The true effect of different Tyre/Wheel combinations can be measured when a Ramp Up, then Ramp Down, is performed on a Chassis Dyno, and half the difference between the 2 runs is the Drivetrain Inertia. Not one of you would of ever had a Ramp down performed on your cars, as it is not great for Turbo Charged cars, and any owner would grimace in pain watching their car being ramped Down. People in the racing industry are normally the most interested in measuring Drivetrain Inertia. The differences you are seeing are quite normal. I recall a BMW M3 that I had dyno'd many times at 170RWKW with the standard wheels, the owner then fitted some 20" wheels and the Power fell to 150RWKW. I've also seen a WRX pick up 8AWKW from just changing to a lighter set of wheels.

You seem to be a liar, as this GTR was only run in 4WD, and 338AWKW was the highest reading, the second run it dropped to 317AWKW and the car then left the dyno, the owner stated that he gets over 370RWKW on his own dyno in 2WD. I can post up the Graphs of both runs if you like, and I'll post a Torque Split graph that proves the car was run in 4WD, all with the time and date clearly displyed on the printout. You really seem to have your facts wrong, maybe the trip up from Melbourne was a bit too much for you and you need to go beddy-by's.

Harry, (on behalf of Dyno Dynamics, as he works for them) has now stated that the difference between 3 runs with different Shootout Modes on the same vehicle can be put down to Inertia. Quote “what do you expect, they are using different inertia”. The inertia he would be referring to is Dyno Inertia and Vehicle Inertia. The Dyno Inertia, as stated on their website is 2.59k/m^2 (single retarder), this can be acurately measured as each component in the dyno can be broken down to individual components and their respective inertia calculated, then all added together to get 2.59kg/m^2. Once the inertia is known, you can then work out how much Torque it takes to accelerate the rotating dyno components at any given Ramp Rate (Angular Acceleration). For eg. Using 2.59kg/m^2 at a ramp rate of say 10klm/h/sec, (this is you car accelerating at a rate of 10klm/h every second on the dyno) this equates to 66.31Nm or 48.91ft/lbs of torque. This means that 66.31nm is being added (in the software) to the measured torque at the Load Cell (this is the component that measures how much torque is being produced on a Chassis or Engine Dyno). If you use a Ramp Rate half as slow, ie 5klm/h/sec, there would only be 33.155Nm being factored in, and if you use a Ramp Rate of 20klm/h/sec then the inertia is now 132.62NM (Ramp Rate 20 was the rate used on the APS BA Turbo at the Melbourne Expensive Daewoo Ford Show, clearly states this on the Dyno Printout). There is nothing wrong with applying Dyno Inertia as the car has to make the torque to accelerate the rollers at any given ramp rate. On most vehicles, you can change the ramp rate from a very slow to reasonably fast and the power at the wheels should be very close, this is because it has appropriate Dyno Inertia. Once you try to ramp a vehicle on a dyno faster than it actually could accelerate on the road, the measured power will start to fall away as you are no longer measuring Brake Horsepower, this is easily seen on turbo vehicles as a drop in boost produced, as in the example vehicle in the thread starter, but, the vehicle in question somehow made more power? The other factor that will then be used to somehow explain the 30KW extra is Vehicle Inertia. Vehicle inertia can be meaured as such, perform a graph at any given ramp rate, see at what road speed the vehicle made its maximum power, then manually hold the vehicle at full throttle at that road speed momentarily and compare the difference, the manually held speed reading will be higher as inertia is only applicable when acceleration (graphing) is being undertaken, the difference is vehicle inertia. On some cars, vehicle inertia is very small, ie rear engined race cars with integral gearbox/differential units with magnesium race wheels, other vehicles such as 4WD’s have much more vehicle inertia as the single biggest contributing factor with any inertia is Diameter, things like tailshafts and axles don’t produce signicant amounts of inertia. The question that comes to mind then is, why should an XR6 Turbo use a different ramp rate (or Shootout Mode) to an XR8, as the drivetrain inertia difference between the 2 cars would be bearly measurable, the only difference being 2 extra bigends and the extra crank material, on again, at the back wheels, bearly measurable. The next question then is, why should a Supercharged XR8 have to use Shoot81, as clearly the drivetrain inertia would not be any different from a N/A XR8 other than a supercharger belt and pulley, does this equate to 12Kw, I don’t think so, remember we are talking about inertia here and not power required to turn a supercharger. What these different Shootout modes clearly have are some sort of fudge factor the faster the ramp rate, this then poses the problem, at a local worshop dyno day where someone is going for outright power hero wank status, the person who has a 6cyl vehicle will be clearly disadvantaged against someone who has a V8 or Supercharged V8, think about this because alot of your XR6 Turbo’s can quite easily make more power than an old 5 litre Late model camira with one of those centrifigul blower kits, but you’ll be very disadvantaged because you’ll have to use Shoot6. Just my thoughts, flame away.

I don't think the original author was disputing that you wouldnt get repeatable results from 4 different dyno's. What he brought to light was the fact that when the faster ramp rates were used, the displayed power seems to be being "bumped". Sure, Shoot81 or whatever is meant for V8 Forced Induction, not a 6 Cyl, but at the end of the day, how does the dyno know that it now has a 6 cyl sitting on it and not a V8, should it matter? I think us as punters who go to the Summernats or Holden/Ford show and see twin turbo V8's producing 1000hp at the wheels will now be very sceptical about these numbers as if you go by the example, the power reading could be fudged by at least 15%, real honest.