[Trimark]

I have been to a tuning shop today to dyno my car and before the measurement the mechanic unpluged the transfer case actuator to make the car rear wheel drive only.

I was told that it is a normal procedure to avoid any issues with the TC during the dyno. Everything went smooth, the car was in dyno mode and only the rear axle worked. After the test there were no error codes.

Is it possible to use the car permanently with the TC unlpuged?

[Ron1n]

I wouldn't. And finding a proper AWD dyno is a better solution, since just dynoing rear wheel doesn't actually give you what you're looking for.

[Boosted_8]

This is the same hack X3/5 owers with broken actuator wheels have been using to drive the car until they have the chance to repair. It's not ideal as it disables all stability and abs.

[Trimark]

Originally Posted by Boosted_8

This is the same hack X3/5 owers with broken actuator wheels have been using to drive the car until they have the chance to repair. It's not ideal as it disables all stability and abs.

Thanks, good to know

[430Scud]

Originally Posted by Ron1n

I wouldn't. And finding a proper AWD dyno is a better solution, since just dynoing rear wheel doesn't actually give you what you're looking for.

Can you explain how that is?
Thanks

[Ron1n]

Originally Posted by 430Scud

Can you explain how that is?

Using a RWD dyno on an otherwise AWD car? The powertrain loss is different between the 2, and if you're actually in AWD aside from the dyno, AWD powertrain loss is higher than just RWD, so the numbers will be lower when out on the street.

[mrgicm]

Originally Posted by Ron1n

Using a RWD dyno on an otherwise AWD car? The powertrain loss is different between the 2, and if you're actually in AWD aside from the dyno, AWD powertrain loss is higher than just RWD, so the numbers will be lower when out on the street.

That is correct. Then it is not a correct dyno. Your best solution is a xhp tcu flash enaing only rwd. That way what you dyno is what you have on the street.

[Trimark]

Originally Posted by mrgicm

That is correct. Then it is not a correct dyno. Your best solution is a xhp tcu flash enaing only rwd. That way what you dyno is what you have on the street.

The dyno test result was in line with the factory specs (horsepower and torque on the axle), the curves were according to the book.

I guess the horsepower on the wheels and the power loss curve was incorrect.

Unfortunately xDelete is not available for the G30.

[Boosted_8]

My understanding of BMW's performance Xdrive is that the majority if not all torque is sent to the rear diff unless there is slip, in that situation the front transfer case is computer controlled to redistribute torque to the front diff. So in conditions where the car has full traction at the rear and above certain speeds, its effectively RWD anyway. Therefore a RWD dyno reading isn't deviating much from what's happening on the road. BMW's system is not permanent AWD like a 1990's Audi Quatro or a Land rover defender, its more like a reverse VW Haldex system.

[G50]

Originally Posted by Boosted_8

My understanding of BMW's performance Xdrive is that the majority if not all torque is sent to the rear diff unless there is slip, in that situation the front transfer case is computer controlled to redistribute torque to the front diff. So in conditions where the car has full traction at the rear and above certain speeds, its effectively RWD anyway. Therefore a RWD dyno reading isn't deviating much from what's happening on the road. BMW's system is not permanent AWD like a 1990's Audi Quatro or a Land rover defender, its more like a reverse VW Haldex system.

It isn't a reverse of haldex. The front wheels are always driven. The system can send less power to the front if the front wheels are slipping, but I don't think there is a situation where you would have no power going to the front axle.
"In the standard system during normal driving, 40 per cent of the power is sent to the front wheels and 60 per cent is sent to the rear. Then, when sensors detect wheel slip, power can be diverted forward, backwards or to individual wheels to help maximise grip and keep the car stable"

[Boosted_8]

Originally Posted by G50

It isn't a reverse of haldex. The front wheels are always driven.

I disagree with this statement. If the M550i system operates in the same manner as the F90, 100% of torque can be sent to the rear and then further distributed to either rear wheel by the sport differential. 40/60 is the default torque split.

With respect to the the original poster, when running in forced RWD if the correct run down (drive loss) factor is applied or (measured on the rollers in gear like a MAHA dyno does), there is no reason why the power measurement wouldn't be accurate with the transfer case unplugged. Would I want to tune the car in this state? no.

[G50]

Originally Posted by Boosted_8

I disagree with this statement. If the M550i system operates in the same manner as the F90, 100% of torque can be sent to the rear and then further distributed to either rear wheel by the sport differential. 40/60 is the default torque split.

Fair enough. What situation would the car send all the power to the rear?

Front wheels on ice, rear on Tarmac?

I can't think of any situation where the front wheels would have such limited grip that the system wouldn't send any power that way.

A haldex system is FWD only in normal driving, until slip is detected and the viscous coupling sends a maximum of 50% of the power to the rear.