Power split ratio
 

There is a SVX for sale near me and the seller says that the SVX is fwd until the rear wheels detect wheel spin. It got me thinking, what is the power split between the front and rear wheels with a stock transmission. Nothing urgent just interested in knowing. I was thinking that it was like 30% to the front and 70% to the back, but its just a ratio that popped into my mind.

Re: Power split ratio
 

It varies from 50/50 to 90/10 based on quite a few input signals. Contrary to many people's thoughts, it rarely ever actually sees the full 90/10 split. It also does not need to detect wheel spin to go to full 50/50 split.

Re: Power split ratio
 

It starts 90/10 going up to 50/50, depending upon the amount of slip detected.

Re: Power split ratio
 

gives up....

Re: Power split ratio
 

I had heard, I think its correct the only time its even close to 90/10 is flat highway with steady throttle input.

Other then that its fairly generally 80/20

Re: Power split ratio
 

Re: Power split ratio
 

Ok. Now that Captain Picard has had his say, here's the answer. (For those playing along at home, it's exactly what Nate said.)

The transmission can vary the torque split between 90 front / 10 rear and 50 front / 50 rear. This is continuously varied as the car is driving, and it doesn't simply stay at one percentage split in "normal" conditions. It's always changing.

This information is ONLY valid for the USDM style multi transfer clutch AWD system in the 4EAT.

Re: Power split ratio
 

From what I remember from when I was driving with Tom with his select monitor connected (with which he could monitor the split in real time), a lot of what went to back wheels depended on how hard the gas pedal was hit.

Re: Power split ratio
 

Yes, I think it tries to anticipate wheelspin before it actually happens. Just like getting power mode to come on requires that you press the gas pedal quickly. It's looking for the TPS voltage signal to change very quickly, not just change. That way it can send power to the back wheels preemptively.

But still, that's only one input. There's still the two speed sensors for the front and rear wheels that it can compare, the speed that the car's actually going, the position the shifter is in, and maybe something else. It's more complicated than just "front/rear 90/10 normally and 50/50 if it's slipping".

The 30/70 number you're probably thinking of the VTD (euro/aussie/jdm) type of trans which is rear-biased and which only got to the US in later subarus with the phase 2 4EATs.

Re: Power split ratio
 

With the exception of having left out "constantly variable" from 90/10 to 50/50, tell me how this is not true of a Phase 1 style Subaru 4EAT. It is direct from Subaru documentation. I did not say that there are two settings of only 90/10 and 50/50.

Re: Power split ratio
 

It doesn't detect slip to transfer power. That is completely false. It also, literally, NEARLY NEVER sees 90/10. It is a completely false statement. Subaru states things so that it is simple to understand.

If they stated, well, it varies power based on speed sensor signal taken from VSS1 and VSS2, TPS signal as well as taking into account vehicle speed, specific shift map it's currently in as well as whether the cruise is on or not, that's a lot harder to understand. So they tell people that it's 90/10 until it slips. When people hear that, they think, "Oh, it's mostly FWD so it probably makes it get much better gas mileage that way."

Go get a SSM and hook it up. Let me know the circumstances you actually see 90/10 :)

Edit: If it had to detect wheel spin, every 4.44 swap would spin the front wheels before harshly engaging the rear when going full throttle from a stop. It doesn't do this if everything is working properly.

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Re: Power split ratio
 

But, but, but.......

My Uncle Charlie's first wife's second cousin's husband said that......(fill in the blank).


Feel free to add this response to EVERY answer EVER given by anyone who is TRULY more knowledgeable than the asker of the question.

:p :D

Re: Power split ratio
 

Slip is probably a terrible word to use, because you're right, people are going to assume wheel spin. What is 'slipping' is the transfer clutches. I do not have the opportunity to hook up an auto SVX to a SSM, but I have had the chance to do so with other phase 1 4EATs when I worked for Subaru, and you will see 90/10, but it's not under real-world conditions (ie: no real load on a lift).

Re: Power split ratio
 

Thanks for the answer everyone, man I love this forum :D

Re: Power split ratio
 

i am very disappointed... when i was doing my research about the SVX i read the 90/10=>50/50 but i always thought it was 90 rear 10 front!!!:eek: seemed more reasonable that way:D (but now it explains why you can convert it to fwd with just a fuse!)
i'm pretty sure that the censors do a great job of keeping it away from the fronts because it never feels (to me) like a FWD car out of corners...