From a German Evo site:

https://evo-forum.de/index.php/Threa...rlustleistung/

Drivetrain loss Evo with ACD und AYC :

17”, 235 45-17 Serien BBS 8x17: 75 hp@7000
18”, 235 40-18 Team dynamics 8x18 : 96 hp@7000
18”, 255 35-18 OZ Ultra 9x18 : 105 hp@7000

same dyno, same day, only wheels changed
Max engine power in all 3 cases 386 hp +- 3 hp
Boemanns Maha 3000
Measurement (2500 - 7500 rpm ) 22 seconds

Drivetrain loss Evo w/o ACD w/o AYC (US Evo8 2003) :

17”, 235 45-17 Serien BBS 8x17: 53ps@7000
18”, 235 40-18 Team dynamics 8x18 : 71ps@7000
18”, 255 35-18 OZ Ultra 9x18 : 82ps@7000

same dyno, same day, only wheels changed
Max engine power in all 3 cases 521 hp +- 3 hp
Maha dyno
Measurement (2500 - 8800 rpm ) 20 sekunden

 

ACD/AYC

17" 19.4%
18"*8" 24.8% Δ+5.4%
18"*9" 27.2% Δ+2.4%

no ACD/AYC

17" 10.2%
18"*8" 13.6% Δ+3.4%
18"*9" 15.7% Δ+2.1%

Assuming this "table" comes out correctly it should be easier to grasp.

Is AYC really eating nearly 10% of your power before it gets to the ground? I am assuming on a dyno it is essentially doing zip, straight line. But two different engines, no mods listed and all that.

There is a reason I am not in a hurry to get rid of my 16" A-tech wheels that weigh something like 13lbs a piece.

 

How is the loss being measured?

 

Drivetrain losses aren't a % of power.
One day people will move past that ridiculous idea.

My question is what gear is it being done in when on the chassis dyno?

 

They are, and it increases non-linearly as power is increased due to more load causing more friction in the drivetrain.


Take my civic for example: it makes 200hp at the crank. Most of them dyno in the 150-160whp range. Its FWD, so basically most of the loss is in the trans. But, if you pull the trans out of the car, you can spin it by hand. If the trans used a fixed number of HP, I can tell you that I wouldn't be able to spin it by hand because my hand does not make 40-50hp, it doesn't even make 3hp...

 

I am the Person who did these tests.

Test were done on an Maha 3000 Dyno, its an Load holding Dyno like the Mustang Dynos 500 series in the US.

Dyno is set to brake in an way that the Acceleration at the wheels is constant Delta Rpm / second. in this case for the Low power car it was 230 RPM Engine / second in all 3 runs.
4 Gear for all tests

Losses are calculated by Rolldown in neutral gear after the run is completed.

Rollout will sample the data of the rotation items ( Drivetrain , Wheels Tires and so on ) for their rotational mass. This mass is "taking" Power when it has to run Faster aka acceleration.
A Rotating / Accelerating Item with an mass will have an moment of inertia (MoI) which will be higher for the following reasons:

1. The higher the weight the higher the MoI
2. The bigger the distance from the shaft where the weight sits the higher the MoI
3. The faster the acceleration will be , the higher the MoI

To get an Precise measurement at the Wheels for Power and Torque you will do an Sweep run to find the spot where the Max power is Produced.

The the dyno ( Load holding ) will be set up so that it will HOLD the Engine RPM steady at this given RPM you found for max Power.

When the Engine RPM is coming to that point under WOT, the Dyno will add Brake force to hold it steady.
Then the Torque at the wheels will be measured.
Since the wheels will also rotate at an constant speed, the Rotational MoI goes to zero since no acceleration will happen anymore.

So you get the REAL WHP and the REAL Drivetrain losses. These are static and only used for figuring out real losses. In the real world you will have always an acceleration, so the Rotational MoI is always higher than Zero.

In conclusion: on an inertia Dyno you will see the following:

The higher the Power of an car is, the rollers will accelerate faster since the mass is constant. But it takes more Power to Turn the Wheels in that way.
The dyno will compensate the Rollers, because the Mass is Known and also the diameter of the MOI Point of the rollers is known.

But the Tire Wheels combo is not Known and is only estimated. So you will mostly see an lower WHP than what is really there.
On the Street you will have lower Power to the Ground when the acc. is faster than on the dyno and more power in the higher gears since the acc. is slower.
On some dynos ( Inertia ) the run from 2500 to 7500 RPM can be as short as 6-9 seconds, so they will show 4 gear Power on the street.
In 5th gear at the street it takes much longer to accelerate through these RPM..

In conclusion :
The very same car with an smaller diameter rim, same width and same tire diameter and width ( iE 17x8 vs 18x8 both with 235 Tires but same scope ) will accelarate faster in the lower gears.
In 4th / 5th gear, when Air drag is the mayor factor, they will equal out.

On low torque Engines like 1.6 L NA Cars that will become an HUGE factor...
Bigger and heavy Rims...and the car becomes a massive slowdown during acceleration...but the top speed remains the same.

For anybody who will have an proof to test at home:

Get an Bicycle Upside down, an try to accelerate the front wheel to some Rpm.
Use only an pencil at one spoke.

Using less force, the acceleration will be lower but it will rotate easy to an dedicated rpm

Using more force, The acceleration will be faster, but its likely not possible to hold the pencil.

Since we not changed the Wheel itself, you discover the Rotational MOI !!

Thats also the reason why you will much more Throttle to accelerate to say 35MPH, but when you reached that and hold it steady you have tho back off the throttle. ( Running on Dyno , not on Street, because there is also the mass of the car itself which has to Accelerate )

What i found so far is that an Typical " REAL " Drivetrain Loss in 4th gear / 6500 RPMEngine in an Ayc Car is app. 10 to 14 HP

Here some Power requirements needed for 200KPH ( 125 MPH ) steady for an EVO 7 stock Wheels

Roll loss for tires : 5HP
Drivetrain: 11HP
Air Drag : 120 HP

Total: 136 HP

Same for : 250KPH ( 155 MPH )

Roll loss for tires : 7HP
Drivetrain: 14 HP
Air Drag : 245 HP

Total: 266 HP

 

^^ Good stuff


There are two main losses in gear systems. Gear efficiency and fluid/contact friction.

1. Gear efficiency
Gear efficiency has very little sensitivity to torque once you get up to a certain level. They are actually MUCH LESS efficient at lower torque levels though because there is some basic friction there that exist regardless of torque (what you feel with your hand). If the efficiency goes non-linear at high torque, it's because shafts and cases are bending and gear mesh/tooth contact has gone to hell...no worries though, it will be loss-less soon enough if that is happening...well, if you call gears out side of the case loss-less anyway?

For a modern helical gear, efficiency is around 97-98%. So 2-3% loss from the drive gear in the EVO transmission as it's a 2-shaft transmission. Sure their are other gears floating around, I'll get to those in a minute.

Hypoid Ring and Pinion gears can introduce much higher losses and the evo has 2 of them. Efficiency varies widely but I'd put money on saying it's pretty efficient on the evo. I'd guess 95% range so 2* 5% = 10%

You are likely in the 12%-14% range for gear efficiency. That portion is HP dependent in that it will be a fairly linear loss percentage.

2. Fluid/Contact friction
All those spinning parts cause fluid motion. There are losses associated with that fluid motion. They will be speed dependent as the faster you spin the gears, the more the fluid moves. Just a SWAG It's probably on the order of a couple percent at operating temperature and at high speeds.

There is also contact friction on all the bearings and free wheeling gears. There will be a static amount due to bearing pre-load and then a portion that is speed dependent.

This is talking "static losses" like german_evoVII is talking about.
Like he mentioned, you also have "losses" due to rotational inertia. This is why lightweight clutch assemblies, superlight wheels/tires, lightweight driveshafts, lightweight brakes all make a noticeable difference in the feel of the car. Particularly in the lower gears. Less is going into the parts, more is hitting the ground.

So...in conclusion, you have a linear percent proportion but you also have a speed dependent portion. On the evo, it's probably 3 parts gear efficiency and 1 part speed dependency. RWD, probably 2:1 and on a FWD, probably 1:1 as they don't use hypoid gears at all.

 

Google "Optimization of Gearbox Efficiency" BR Hohn.

Good stuff. Of Importance though, directly from the paper:
"For nominal power transmission the load losses of the gear mesh are typically
dominant. For part load and high speed, high no load losses dominate total losses."

Figure 14 shows there is a decent amount of loss that is strictly speed dependent that has nothing to do with load. At high speed, it contributes about 1/4 of the total losses under the high load conditions.

50HP at the engine of 500HP at the engine, if the tire is going 125mph, you get that non-power dependent loss and it's not insignificant.

In this case for example, if it's 52HP on the non-ACD at 500HP and 1/4 of that is speed based, then about 13HP at that speed is due to the speed alone and the other 39HP is load based with a total loss of 10%. Crank it to 1040HP and it goes to 78HP load based and the same 13HP for speed dependent. Now it's 8.75% total loss. Or go the other way and drop it to 260HP and you have 19.5HP load based, 13HP speed based and a total loss of 12.5%.

Thus...it's silly to think drivetrain loss is strictly a % of power.

 

In my first post, I should have clarified that the HP number lost increases with power, not the percentage of HP lost. I know that the percentage doesn't increase as power is increased. So, like I said, horsepower loss is a percentage, not a fixed number.

 

But it's not, is the point. A portion of it is, but not all of it. As I demonstrated above, it makes the HP% loss drop as HP output increases. Negating the effects of inertia in all the rotating parts...

 

As the powercurve rises on the rpm range the HP loss% goes down, but the actual horsepower losses are greater than in lower points on the power curve because the actual horsepower rises. Also the lower the gear the greater the effect of inertia, the higher the gear the less the effect.

There are 3 types of loses, frictional loss due to the contact of parts, the moment of inertia loss due to the weight of the rotating parts, and fluid friction loss. All 3 are interrelated. Speed and the centrifugal force applied affects all three, so does heat generated. The greatest percentage in loss belongs to the moment of inertia effect, hence why the hp loss% goes down the higher the gear and the higher an engine revs, but due to the fact that the output horsepower rises greatly as the engine runs a higher gear and as the revs rise the actual hp loss rises also.





Marios