is acd better than non-acd for track use?

[boomn29]

Originally Posted by supersupra

In wet it makes a lot of difference.

I agree.

For instance, if it's wet out I can put the ACD in Tarmac mode and spin the tires from a roll on some pavements.
If it's in Gravel mode (ie the wet mode) in the same instance; same streets - it won't spin them.

Track:
The Tarmac mode - when it's wet on the track - requires more finesse to safely get the car through turns w/o drifting and kicking out the rear. Whereas if you switch it to Gravel, you can kinda drive the same and it'll protect you. So my conclusion is it helps you save the car.

I track the car in Tarmac exclusively when it's try.

[donour]

Originally Posted by Richard EVO

The '04 RS was the first U.S. Evo with the helical (not viscous) front diff.

Um...I was talking about the center diff. I don't think any evo has ever come with a viscous coupling front diff.

d

[Warrtalon]

Originally Posted by boomn29

For instance, if it's wet out I can put the ACD in Tarmac mode and spin the tires from a roll on some pavements.
If it's in Gravel mode (ie the wet mode) in the same instance; same streets - it won't spin them.

Are you sure? There should be no difference in a straight line, because the ACD only activates when turning.

[Richard EVO]

Originally Posted by donour

Um...I was talking about the center diff. I don't think any evo has ever come with a viscous coupling front diff.

d

ok. thanks for explaining.

[boomn29]

Originally Posted by Warrtalon

Are you sure? There should be no difference in a straight line, because the ACD only activates when turning.

Yep. Could have been a difference in the road surfaces - but this was the same road, just a stoplight apart.

[DaveK]

Originally Posted by Warrtalon

Are you sure? There should be no difference in a straight line, because the ACD only activates when turning.

I would've thought ACD should also be responding to differences in wheel speed between the fronts and rears, meaning that if you have wheel spin in a straight line, it should be kicking in to lock down so that the fronts and rears spin together.

Dave

[kaonashi]

Im def sticking with Non acd in the future when i get the xfercase rebuilt. Im not done tearing up my spidergears in it yet though but i drag only no autox/rr for me

[pepe le pew]

thanks for the discussion, everyone. i appreciate the help.

Originally Posted by donour

The fastest Evos (Daddio, Berry, showcase) were all ACD cars. If you are going to do anything with this information other than just pass the time, they are the ones you should listen to.
d

this is quite an insightful observation. thank you for pointing that out.

[Jeff_Jeske]

^^ Insightful sure..... but the very very few non-acd cars have a front LSD and that makes a world of difference.

[toovira]

Huh....interesting responses in the "feel" that most people, there are no difference.

I would also agree with the assessment that ACD wouldn't make much of a difference in most average drivers.

I feel a big difference in cornering between Gravel and Tarmac mode when I'm running on tarmac. I have found that in Tarmac, the car is fairly neutral/slight oversteer in hard cornering.

One day I was playing in dirt with Gravel mode...went on the road....forgot to switch back to Tarmac. I went through a hard corner on the road....surprise! my car was heading straight when steering wheel turned....yes, it understeered. Ya apply slight braking and all is good.

If it's any help, the (Skip Barber) racing school instructor had the same opinion that on tarmac in Tarmac mode, the car is slightly neutral/oversteer. While in Gravel mode on tarmac surface, the car understeers quite a bit.

Does ACD help? Definite yes for me.

Now I've never driven non-ACD before (well....I have, but before I learned how to REALLY drive)....so I don't have an opinion about that.

I don't know when ACD works or not, but assuming that ACD is active all the time....even straight line....the physics make sense. For Tarmac on tarmac surface, 70% rear 30% front.....weight of the car is shifted to the back under acceleration.

I'm sure you've seen this, but see this thread:

Motec ACD Controller = AWESOME

[4cdndctn]

There's a lot of focus and chatter surrounding a modified rear diff at the moment as many say it's a cheap and effective modification to help loosen up the car.

I do not have it nor do I endorse it, but depending on what you are looking to achieve, it may be an option for you.

[Lancerguy'03]

Originally Posted by donour

I don't. I prefer my '04 RS which has the viscous coupling unit. Another thing to consider is weight. My car weighed 3076 lbs with the OEM battery,OEM seats, full interior, an added radio, 19 lb wheels, a full tank, and a heavier than stock exhaust.

d

are you serious our car weight that much!? that is less than i thought.....how accurate is that mesurment?

[RallyDSM]

Originally Posted by DaveK

I would've thought ACD should also be responding to differences in wheel speed between the fronts and rears, meaning that if you have wheel spin in a straight line, it should be kicking in to lock down so that the fronts and rears spin together.

Dave

You are correct on this. When you accelerate hard on pavement, dry or wet, you are transferring weight from the front to the rear of the car. On wet pavement, that lifting of weight from the front wheels will make them MORE likely to slip and spin hemorrhaging all your power out from under your front wheels until the weight is evenly distributed again.

With the ACD correctly engaged, the weight transfer and resulting slip from the front tires would be managed and both wheel spin and the loss of forward acceleration would be greatly reduced.

As a practical example, if you are every graced with the ability to stand at the start line of a Stage Rally, watch the cars launch from the start. 90% of them will likely be Subarus (yawn) but even so, watch them closely.

You will see the rear end squat, the front lift, the rpms come down, the front wheels spin and then the car level out, gain traction and go.

Then you will see an EVO or an STi with an active center diff... these cars look entirely different.

You will see the ENTIRE CAR squat. Equally on all fours. Then almost donkey-kick off the line with all four tires digging in deep and strong. The rpms don't seem to drop as much either even though the load seems greater. It's like the car launches off a spring board.

It really is a beautiful thing and VERY VERY obvious when observed from the side in a limited traction environment.

I am also a driving instructor so I have also had the luxury of driving many different student's cars. Most without any special diffs but a few with ACDs and I can feel the difference in their cars. ACDs in general, tend to be more forgiving and allow for tighter turning.

WRXs, early gen DSMs and my first rally car, the Celica GT4 and their ilk, realy have a tough time with the really tight corners. Ebrakes don't help much as it tends to lock up ALL FOUR wheels as the shock is transferred back up the driveline to the front of the car. Flicking is the only fast way around a corner in any of these.

However, the ACD really, truly helps these cars DRIVE around a tight corner.

As a side note... many a RWD Rallyist has welded their read diffs completely solid, which would NEVER work on the pavement but totally works on limited traction surfaces. Kind of anti-intuitive.

So, taking advise from ANYONE in the Rally Community should be considered accordingly. LOL!!!

Personally, I'm looking forward to having the ACD on board for the 2008 rally season.

RallyDSM

[4cdndctn]

Originally Posted by RallyDSM

You will see the ENTIRE CAR squat. Equally on all fours. Then almost donkey-kick off the line with all four tires digging in deep and strong.

Better a donkey kick than a donkey punch.




I couldn't resist...

[RallyDSM]

LOL... okay, bad analogy but you get the difference. Maybe a better analogy would have been a coiled cat ready to pounce?

Either way, the car leaps forward rather than lunges.

RallyDSM