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I'm starting to tune the ACD tables on my USDM Evo 8 and I'm particularly interested in improving the tarmac performance, improving lockup and drive out of the corners. As more people recognize how useful ACD/AYC modifications can be to improved handling on the road, track and rally, it's time we started sharing our maps and our knowledge with the rest of the Evo community.
More experienced members can critique and advise the less experienced on how to make changes to ACD tables to get their Evos to handle and perform better in different conditions, so post up your maps!
Please provide the following data to help other members categorize your tune: 1. Year 2. Market (USDM, JDE, EDM etc.), 3. Model (Evo 9, 8, 7, etc.), 4. ACD only or ACD & AYC 5. Description of the modifications you made and how they have improved handling 6. Screen shots of your modified tables
Last edited by CDrinkH2O; Jan 2, 2016 at 02:42 PM.
I'll start with mine...I'm trying out Merlin's mildly moded 401702 ROM
1. Year: 2005
2. Market: USDM
3. Model: Evo 8 GSR
4. ACD only
5. Objective: Increase lockup on acceleration out of the corners
Result: Great lockup on WOT increases rotation, promotes over steer and finishes the corner off well.
hm. when i autox, i set mine to "snow" because i feel the car rotates better by delaying lock up (making the car feel more RWD). you had better rotation when having it do so earlier??
hm. when i autox, i set mine to "snow" because i feel the car rotates better by delaying lock up (making the car feel more RWD). you had better rotation when having it do so earlier??
Yes - earlier ACD lock up on acceleration sends more torque to the rear diff, causing it to lock up sooner and the car behaves more like an AWD vehicle should
Can you show us your snow and tarmac A maps so we can see how you are achieving this?
My snow A map locks up harder and earlier in throttle application than my tarmac A map
Last edited by CDrinkH2O; Dec 25, 2015 at 10:50 AM.
Reason: added maps for clarification
Yes - earlier ACD lock up on acceleration sends more torque to the rear diff, causing it to lock up sooner and the car behaves more like an AWD vehicle should
you're saying the ACD unit sends more torque to the rear?
I know how it works, but you stated the ACD sends more torque to the rear wheels and causes the rear diff to lock up sooner.
Imagine you are braking hard for an auto-x turn. As you begin your turn in, the ACD opens fully, and at maximum lateral acceleration, you lift the rear inside wheel. Before the apex, you still are turning hard, waggling that rear inside wheel, and yet you need to get on the gas, to finish the corner off and, to get maximum speed down the next short straight.
As you mash the gas pedal, the ACD stays open, sending 50% of available torque to the front wheels, which try to pull you out of the corner, contributing to understeer. Most of the other 50% of available torque is used to accelerate that inner rear wheel waggling in the air. The outer rear wheel only gets whatever torque was required to overcome the friction of the rear LSD clutches.
The waggling, spinning wheel doesn't lock up your rear LSD, or finish off the corner, or push you out onto the straight. Almost all 50% or the torque supplied by the ACD to the rear axle is wasted spinning the inner rear wheel. Its speed quickly exceeds that of the fronts and the outer rear.
The part of the ACD supplying torque to accelerate your waggling wheel is now spinning much faster than the part supplying torque to the front. At this point as you unwind the steering, the ACD starts to lock up. The front and rear halves of the ACD are forced to rotate at the same speed and the torque lost to the waggling wheel is returned to the drive drain. Deceleration of the inner rear wheel forces the spider gear pins up the ramp in the rear diff, compressing the clutch plates and locking up the rear LSD, Most of the wasted torque is redirected to the outside rear wheel, you finish the corner faster, get maximum acceleration out of it, and maximum speed on the next straight.
Tuning the A maps to lock up sooner when throttle is applied can increase your speed out of the corners.
Look at the two A maps attached below. The top one is stock and the bottom one is the Ralliart K2 tarmac rally map. Look how much sooner and harder the K2 locks the ACD.
Last edited by CDrinkH2O; Jan 1, 2016 at 09:20 AM.
Reason: Updated image file
I know how it works, but you stated the ACD sends more torque to the rear wheels and causes the rear diff to lock up sooner.
Yes, in anticipation of the front wheels spinning, the ACD locks up, which forces more torque to rear, as opposed to allowing all of it to go to the front due to the front having less grip.
Dec 24, 2015, 10:31 PM
