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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 07-06-2014, 07:25 AM   #43
4wheelinls1
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We get people quoting all sorts of dyno figures in Aus. I wouldn't have personally said the Dyno Dynamics was the benchmark in Aus, Mainline is probably the biggest selling, Dyno Dynamics the easiest to manipulate. I wrote this for a car club before a dyno day to help them understand the differences in dyno's, operators and figures.

Chassis dyno Power and Torque figures.
There seems to be a lot of confusion over rear wheel figures and engine figures. I get queried nearly daily at work about what torque does the car make? Especially when it comes to diesels and specifically the TD42. A chassis dyno measures power and torque at the rear wheels, torque and power at the engine is measured at the flywheel. Manufacturers specify flywheel torque and power figures. The difference between rear wheel torque figures and engine torque figures can be calculated as the difference between engine rpm and dyno roller rpm. eg; A vehicle running on the dyno at 100 klms per hour rotating the engine at 2000 rpm may be rotating the rollers at 1000 rpm. In this case as the speed is half then the torque is double, so halve the dyno torque reading to get the engine torque in this example. If our dyno torque at the rear wheels is 500Nm then the engine torque is 250Nm. Where this becomes confusing to people is they seem to assume the gearbox is the only torque multiplier and that if the gearbox is in 1:1, commonly 4th gear, then the torque is more accurate. Unfortunately this is not the case, there are other torque multipliers that need to be factored in, for example the differential ratio and even the tyre size. If the car is an auto it gets worse still as the torque converter is a flexible joint that’s speed and torque output vary depending on load.
I was recently questioned regarding the validity of the high torque figures generated using 3rd gear on the dyno rather than those of 4th as it would appear people are making comparisons between vehicles based on rear wheel torque. It is true the torque figures in 3rd gear are higher in but I don’t make it that way, the laws of physics do. Rear wheel torque figures are not comparable from vehicle to vehicle regardless of the gear unless the gear, tyre size, pressure, tie down method an diff ratio; are all the same on the same dyno. Torque figures in 3rd will be higher than 4th, by the amount of what the difference in gear ratios is. So if 4th is 1:1 and 3rd is 0.75:1 then the torque will be 25 % higher in 3rd than 4th, and the speed will be 25% lower if everything else remains the same. Another example would be if two cars came in, both TD42 engines. Car one has 35 inch tyres and 3.9:1 diff ratio. Car two has 4.88 and 31 inch tyres. So at 100 kph car one is doing 2440 rpm and car two is doing 3438 rpm at the same 100 kph.(let’s assume the guy with 4.88:1 normally offroads with 37 inch tyres but for the road and a dyno has his street legal 31’s). So in this example the difference in ratio is more than 70%, a greater difference in ratio than the gearbox between 3rd and 4th. For the fairest comparison between these two cars then the car with the 35’s and 3:9.1 should be run in 3rd gear and the car with 4.88:1 should be run in 4th to make a closer comparison between the two as the total drivetrain ratio is most similar.
There are a number of reasons to run lower powered cars in third, most 4wd owners are unlikely to take their vehicles up to 140-160 kph, and higher depending on the gearing, these speeds would be achieved at the top of 4th gear. These speeds with larger aggressive tyres are often hard on the cars and not so good for the dyno with harmonics and vibrations. I have also seen a number of tyre failures at high speeds of aggressive 4wd tyres, delamination, tread separation and blistering after longer use at high speeds. Also a dyno like a torque wrench is most accurate in the middle of its range, ours can read from 0.1 to 1800Nm but a low powered vehicle, less than 80 kW is going to show more accurate figures in 3rd as the load cell will measure more torque in 3rd than 4th making the power calculation more accurate and gains more easy to recognise.
The power figure will be the same regardless of gear, with the exception on the influence of friction. The loss of speed equals the gain in torque and vice versa. If comparisons are being made between cars then they should be made based on power not torque unless you can be 100% certain the two vehicles are of the same tyre circumference(size, wear and pressure), have the same diff ratio and are in the same gear.
A chassis dynamometer is a rolling road with the capacity to simulate real driving under various load and speed conditions.
First we need a basic understanding of a few physics principles. Firstly F=ma, where F= force, m is mass and a is acceleration. This is Newtons second law of motion. The way a Dyno works is to measure the force exerted by the vehicle, by also measuring the speed of the wheels the power can be calculated. The force is measured in torque by a strain gauge, the braking force is generated by a load cell, this can be electric, hydraulic, water or even friction(Inertia). Electric is the most common form of load cell, often referred to as a retarder. The load cell is mounted to the rollers, and applies an opposing load to the vehicle, this is where Newtons third law comes in. For every action there is an equal and opposite reaction. In a stationary load situation, constant throttle and speed, the dyno is matches the load generated by the vehicle. The resistive force of the retarder is measured at the strain gauge and converted to torque.
The power is calculated with the addition of a speed input, the roller speed is measured and then put into the formula power=torque x speed/5252. 5252 Is a mathematical constant. One horsepower is defined as 33 000 lf-ft/minute. A one foot circle has a circumference of 6.2832 feet, as these are both constants you can divide 33 000/6.2832 which gives 5252.
All dynamometers work on this principle, measure the torque and the speed, plug the values into the formula and hey presto, Horsepower.
So based on this all dyno’s should read the same, but they don’t…why.
One big problem is Friction. Friction resists all movement and comes in many forms, some we think of and some we forget. On the road wind creates a huge amount of friction; this is why roof racks and raised 4x4s lead to poorer fuel economy as it takes more power, therefore fuel, to overcome the additional friction. The bearings in the axles, the differential gears, the transmission and universal joints all resist movement due to friction and therefore take some power to drive, these parasitic losses are not measured at the wheels, the dyno will only measure the power that is left , because of this any reduction is friction will result in a higher measured power.
Frictional losses don’t end at the car though; the dyno rollers themselves are large and heavy and sit on large roller bearings. If you ever had the opportunity to spin a dyno roller with your feet you’d be lucky to be able to rotate the rollers at any more than 5 kph, the car is rotating them at speeds in excess of 200 kph. The effort exerted to rotate the dyno rollers is considerable; it is considerably lessened if the vehicle only has to turn 2 rollers not 4. As the size and weight of the rollers varies from manufacturer to manufacturer it also stands to be true that different brands of dyno’s will read differently, smaller lighter rollers, or no rollers at all such as in a hub dyno which also removes the mass of the wheel are quite correctly going to read higher, the misconception being the engine is more powerful when in fact the losses are just lessened.

We made this video to demonstrate the large differences in power measured purely by changing how the car is tied to the dyno.

https://www.facebook.com/photo.php?v...type=3&theater
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Old 01-26-2016, 01:45 AM   #44
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Chassis dyno Power and Torque figures.

There seems to be a lot of confusion over rear +whp and +fhp. I get queried nearly daily at work about what torque does the car make?

A chassis dyno measures power and torque at the wheels,

torque and power at the engine is measured at the flywheel.

Manufacturers specify flywheel torque and power figures.

The difference between chassis dyno's torque figures and flywheels dyno's torque figures can be calculated as the difference between engine rpm and dyno roller rpm.

"eg; A vehicle running on the dyno at 100km per hour rotating the engine at 2000 rpm may be rotating the rollers at 1000 rpm"

In this case as the speed is half then the torque is double, so halve the dyno torque reading to get the engine torque in this example. If our dyno torque at the rear wheels is 500Nm then the engine torque is 250Nm.

Where this becomes confusing to people is they seem to assume the gearbox is the only torque multiplier and that if the gearbox is in 1:1, commonly 4th gear, then the torque is more accurate.
Unfortunately this is not the case, there are other torque multipliers that need to be factored in, for example the differential ratio and even the tire size.

I was recently questioned regarding the validity of the high torque figures generated using 3rd gear on the dyno rather than those of 4th as it would appear people are making comparisons between vehicles based on rear wheel torque. It is true the torque figures in 3rd gear are higher in

but I don’t make it that way, the laws of physics do.


Rear wheel torque figures are not comparable from vehicle to vehicle regardless of the gear unless the gear, tire size, pressure, tie down method an diff ratio; are all the same on the same dyno.

Torque figures in 3rd will be higher than 4th, by the amount of what the difference in gear ratios is.
So if 4th is 1:1 and 3rd is 0.75:1 then the torque will be 25 % higher in 3rd than 4th, and the speed will be 25% lower if everything else remains the same.
Another example would be if two cars came in, both TD42 engines. Car one has 35 inch tyres and 3.9:1 diff ratio. Car two has 4.88 and 31 inch tyres. So at 100 kph car one is doing 2440 rpm and car two is doing 3438 rpm at the same 100 kph.
(let’s assume the guy with 4.88:1 normally offroads with 37 inch tyres but for the road and a dyno has his street legal 31’s).
So in this example the difference in ratio is more than 70%, a greater difference in ratio than the gearbox between 3rd and 4th. For the fairest comparison between these two cars then the car with the 35’s and 3:9.1 should be run in 3rd gear and the car with 4.88:1 should be run in 4th to make a closer comparison between the two as the total drivetrain ratio is most similar.
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Old 01-19-2018, 05:32 PM   #45
Jaden
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personally...

Quote:
Originally Posted by Element Tuning View Post
The Dynajets I've been tuning on read pretty low. My FRS baselined at 150 whp (6 speed). Another I tested the owner's car baselined 159 whp. For NASA testing I use these because they don't read far off a Mustang I also use so if I use the Mustang and have to add +10% it's a big penalty.

It's really just about the delta so as long as you have a good baseline any dyno will do the trick really. Customers don't always see it that way as it's more glamorous to use a dyno that gives you an extra 30 hp even though the delta from stock is the same.

Thanks,
Phil Grabow
It's not using a dyno that gives you an extra 30hp, it's NOT using one that jips you 30 hp.

If you believe that a rwd car is losing 25% in drivetrain losses, I have a bridge in Arizona to sell to you...

Jaden
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