4A or 2H? Which is the best?

[BigGreenPony]

Gotta look at Boost, can’t just consider RPM by itself. The two are related but don’t directly correlate

it shouldn’t matter. Mass flow rate is mass flow rate. Turbo or no turbo.

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[Brian_B]

it shouldn’t matter. Mass flow rate is mass flow rate. Turbo or no turbo.

Mass Flow rate and turbo boost are directly linked.

RPM and Mass Flow rate are not.

Just go rev your engine sitting in Neutral.

 

[mpeugeot]

BSFC is all that matters regardless of RPM, Boost, Throttle Position, etc. The lowest BSFC determines the best fuel economy potential at any given point on the fuel map... The better your volumetric efficiency, the lower your BSFC will typically be, and lower BSFC is directly proportional to fuel economy. Sure, spark advance and valve timing play critical roles in the volumetric efficiency of the engine at any given RPM, boost, and throttle position...

Now I will admit that part throttle BSFC doesn't much matter when you treat the accelerator pedal like an on/off switch.

 

[mpeugeot]

Mass Flow rate and turbo boost are directly linked.

RPM and Mass Flow rate are not.

Just go rev your engine sitting in Neutral.

No, turbo boost only indicates the amount of restriction in the system. I can have the same engine with two different turbos, both at the same boost level, and both of them will have very different mass flow rates.

Example - a 1.8 liter motor with a GT28 vs a T3/T4 hybrid at 15 psi of boost will have very different amounts of mass airflow (so much so that there will be 100 HP or more difference in power output at the wheels).

Compare both turbos at a pressure ratio of 2.0 (15 psi of boost essentially). The GT28 is about 25 lbs/min vs the T4 at nearly 40 lbs/min. Also, the turbine plays a large role in this too.

 

[Brian_B]

No, turbo boost only indicates the amount of restriction in the system. I can have the same engine with two different turbos,

This is true - I was kinda assuming we were looking at a given engine setup and not swapping around hardware - but you are correct

 

[Trueblue2296]

I came across this issue by accident. I usually switch my truck to 4A for adverse conditions, such as rain, snow, or sleet. This morning I did not turn it off after a big rain and I noticed that the front end felt a lot tighter and the truck handled reasonable better (Not that the handling was terrible before). So, I now have the question, will running my truck permanently in 4A reduce my fuel economy due to all the extra drive train? Has anyone on this forum tested this?

I'm currently get 18-19 MPG combined on a 2.3 Badlands Sasquatch manual truck.

I run mine exclusively in 4A and haven't noticed a change in MPG at all. depends on how heavy your foot is though. I also don't about MPG too much I prefer performance over MPG.

 

[userdude]

After using 4a for a year, recently put it in 2h for a few weeks. Can't say I like the way it drives in 2h: Definitely more diving and squatting and looser steering. Actually made it feel a little like those children's playground horses on the big springs. Put it back in 4a yesterday and everything is right with the world again.

 

[Tofudude]

I wouldn’t use 4A daily, I’d imagine it’s just extra wear on the clutch pack.

 

[BadmansSAS]

Ford deals in airload.

 

[FleshTuxedo]

Anyone get binding in 4A during slow turns (think backing out of parking spot, pulling in, etc)?

 

[userdude]

Anyone get binding in 4A during slow turns (think backing out of parking spot, pulling in, etc)?

No

 

[FleshTuxedo]

No

Welp, looks like it's gonna get looked at next time I get an oil change.

 

[userdude]

Welp, looks like it's gonna get looked at next time I get an oil change.

Sorry to hear that!

 

[indio22]

I wouldn’t use 4A daily, I’d imagine it’s just extra wear on the clutch pack.

The 2022 F150 shop manual mentions a heat sensor related to the 4A tcase clutch, which can deactivate the 4A if there is too much heat buildup. I don't know if the Bronco tcase is the same, but if needing to measure heat buildup, that is potential for wear/issues and wasted energy. Maybe not likely but there is that additional complexity.

I wonder why even have 2H on 4A models if there is no difference in terms of performance and wear?

 

[Sparkherd]

So, uh, OP and quite a few of ya'll others on here...WTF are ya'll smoking?!?


Transfer Case
OPERATING PRINCIPLE

The transfer case delivers engine torque to the rear wheels and to the front wheels, when requested. The transfer case is mounted on the rear of the transmission assembly. The transfer case has an integrated low range gear reduction using the planetary gear set.

The transfer case has five different operating modes;

• Two Wheel Drive
• Four Wheel Drive - High Range
• Four Wheel Drive - Low Range
• Four Wheel Drive Auto
• Neutral (for recreational towing)

The transfer case is commanded via the mode select switch and the AWD module. The transfer case is electronically shifted via a shift motor mounted on the front of the transfer case housing. The transfer case is filled with lubricating oil which is circulated using a mechanical oil pump. The oil pump is fitted with a strainer to filter any debris.

In four wheel drive mode there is no speed differential between the front and rear axles. This can cause driveline windup when cornering on sealed surfaces.

The Advanced 4x4 with 4A Mode Transfer case is the center of the AWD system. It is a gearbox that attaches to the output of the transmission through a splined input at the transfer case. Torque from the transmission is transferred to the front and rear driveshaft depending on AWD mode.

The transfer case is equipped with an electronically controlled high torque capacity clutch which is located inside the case. This clutch is used to synchronize the speed of the front driveline with the rear driveline during 2WD to 4WD high (4H) or 4WD AUTO (4A) shifts. The clutch also provides torque to the front driveline in all 4WD modes. The transfer case is lubricated by a positive displacement fluid pump that channels fluid flow through holes in the rear output shaft.



Two Wheel Drive Operation

In this mode all torque from the transmission is passed through the transfer case to the rear driveshaft which passes through the rear axle and to the wheels.

Four Wheel Drive Auto

In this mode the transfer case system is active all the time and requires no input from the driver. The AWD control system continuously monitors vehicle conditions and automatically applies torque to the front driveshaft. This is done through the use of a multi plate clutch pack inside the transfer case that modulates torque delivery to a chain drive that is connected to the front driveshaft. I any wheel slip is detected on the vehicle or if the vehicle is in a handling event the AWD control system commands the transfer case actuator to apply torque to a ball ramp cam system which then applies an axial force into the clutch pack.

Four Wheel Drive High Range

In this mode the clutch is essentially locked. This would lock the front and rear driveshafts together giving the vehicle maximum traction. It is a similar mode to the ESOF system 4WD high (4H) mode

Four Wheel Drive Low Range

This mode operates the same as 4WD high (4H) but in addition the torque delivered to the transfer case from the transmission passes through a planetary gear set which multiplies the torque by the given ratio. ( In the case of the Advanced 4x4 with 4A Mode transfer case the ratio is 3.06:1 ) While the torque is increased by 3.06 the output speed from the transmission is reduced by the same 3.06 ratio.

So WTF are these "handling events"?!?
I am pretty sure I cause these on a daily basis...

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