2017 Question on Sport Mode and 4A Mode

[troverman]

So if one was to take the truck to the 1/4 mile - put in 4A ? Or just RWD?

would 4A give you a better launch and switch to RWD farther up the track?

Best result in RWD with a very small amount of brake torquing and then launch. Simply flooring the pedal will not result in wheelspin. Too much brake torquing and you will get wheelspin. Being in 4A means the front drivetrain is forced to spin, which adds a slight amount of drag on the engine. Make sure the A/C is also switched off.

 

[Toadster]

Best result in RWD with a very small amount of brake torquing and then launch. Simply flooring the pedal will not result in wheelspin. Too much brake torquing and you will get wheelspin. Being in 4A means the front drivetrain is forced to spin, which adds a slight amount of drag on the engine. Make sure the A/C is also switched off.

doesn't A/C shutoff during WOT ?

 

[troverman]

It might, but when every tenth counts, best to have the compressor already switched off.

 

[rtmozingo]

Best result in RWD with a very small amount of brake torquing and then launch. Simply flooring the pedal will not result in wheelspin. Too much brake torquing and you will get wheelspin. Being in 4A means the front drivetrain is forced to spin, which adds a slight amount of drag on the engine. Make sure the A/C is also switched off.

No, I've played around with both 2wd and 4A. Only way to not spin your rear tires is to launch 4A. I've gotten 5.2 seconds 0-60 that way. If you can beat that in 2wd I'd love to see it.

 

[tobywan]

I have a question about how 4A works, exactly. A standard transfer case doesn't have any sort of clutch, so you are either in 4wd, or you aren't. With this truck is that still true? If it is some sort of metered torque based allocation, how exactly is that achieved?

Asked another way, is it actually possible to have 25% of the power to the front wheels and 75% to the rear? That would be SUPER cool, I'm just curious how that is achieved.

 

[troverman]

This transfer case has a clutch to power the front wheels when in 4A mode. When in 4H or 4L mode, a mechanical collar locks the front output shaft and the clutch is disengaged.

In 4A mode, some power is applied to the front wheels at all times...probably a very small amount, like 10%. More power is shifted almost instantly based upon a number of parameters, including steering angle, throttle position, ABS sensor readings, drive mode, and more. The clutch can provide 100% lockup or up to 50% to the front tires. The rear *always* gets at least 50% of the power, up to the theoretical 90% if the front always gets 10%. But even at 100% front clutch lockup, it still gets 50%.

The clutch allows the necessary slip to occur during cornering in 4A. That allows front and rear axles to spin at different different speeds. If the ABS sensors detect slip during cornering, more clutch pressure can be instantly applied in a very progressive way that an "all or nothing" part time 4x4 system cannot.

Keep in mind Lariat and higher F-150 trims all already come with a 4A setting on their transfer case, and the way that system works is identical to how the one in the Raptor works. The difference is the Raptor case has the mechanical collar which locks the front shaft in 4H or 4L, just like a part-time case. An F-150 with 4A also has a 4H and 4L setting, but all this does is provide 100% clutch lockup. The Raptor mechanical collar is significantly more heavy duty for longer-duration 4x4 operation, but is no heavier duty than a standard "part-time" 4x4 system like what is found in an XL or XLT F-150, or any Super Duty.

Hope that helps.

 

[tobywan]

Thanks, Troverman, that helps a ton!

Do you happen to know the name or model of the transfercase? Would love to research this more, just for fun.

A couple years ago, I did a bunch of studying of the various locking differentials, would like to do similar with this.

 

[troverman]

Thanks, Troverman, that helps a ton!

Do you happen to know the name or model of the transfercase? Would love to research this more, just for fun.

A couple years ago, I did a bunch of studying of the various locking differentials, would like to do similar with this.

Sorry, I don't know the model. I believe the transfer case is made by Magna and is unique to just the Raptor. I also believe it is based upon the F-150 transfer case design and uses the same 2.64:1 low range ratio. As you know, the rear diff can be selectively locked and if you have the Torsen front diff, you get an extremely good limited slip diff. Oddly, the Raptor will not allow a locked rear diff in 2WD mode while the F-150 (and Super Duty) will.

 

[tobywan]

I crawled under the truck, it's a Borg Warner tcase. I can't find any actual specs online to match the numbers, but if you search for Borg Warner "Torque on Demand", there are lots of general comments.

 

[troverman]

Cool. Borg Warner makes a lot of quality components. The standard Torque on Demand does not include the locking collar, though...as I mentioned above.