I have a neutral handling car but I am considering reflashing the ACD and upgrading to the twelve plate diff.

For those that previously used a higher spring rate in the rear to eliminate understeer will the combination of these upset the stability specifically in long sweepers where you are on the throttle?

 

I am not concerned about autocross behavior. Only large track high speed performance.

 

Subd for info. Very good question here.

 

I was discussing using a ACD in my super touring evo. Charlie explained to me that it would not be a benifit in road racing ie 3rd and 4th gear corners. Tighter 2cd gear rally corners are where a ACD helps. As far as spring rates are concerned we do not have a big difference between front and rear weights using the viscous diff. On super speedway tacks like rovals you want a car to understeer a bit so you Know where the limit is. Regular road racing tracks like Mid Ohio can be set up with trailing oversteer.

 

This is from fast road experience rather than track use: Can't comment on viscous vs. ACD, but reprogrammed ACD vs. stock ACD will eliminate trailing throttle understeer in fast sweepers. Did not feel the need for a RSB with 12-plate and ACD reprogrammed. So, yes I would think less rear bar or spring rate in the rear w/ both reprogrammed ACD & 12-plate. Car can be steered with the throttle, even at higher speeds but maintains a basic slight understeer attitude w/ that set-up.

 

I have the ACD reflash by ACD-tuning, 25mm RSB on soft and restacked factory diff. It works well for faster corners and will power oversteer at lower speeds. I'd recommend the flash because it tightens up the pumps behavior and makes it more sensitive.
I'd try the restack before the 12 plate if its a street car. My car chatters the tires around corners and parking lots and is a little annoying. The 12 plate will be more aggressive.

 

If you have a neutral handling car, why make any changes?

 

I have the stock ACD flash and I have been noticing it more and more this year. It was noticeable during AutoX but I haven't done that for a while so it kind of fell to the back of my mind.

During low speed corners at the track, when the ACD kicks in on corner exit, it disrupts the car. It feels like I'm jumping a curb and unsettles pretty much everything in the car: the steering, the tires, and even the turbo and engine both stutter for a second.

I am on street tires. Would the increased grip of semi-slicks marginalize the activation? Do the ACD reflashes make the ramp rates more reasonable or do they just turn everything up?

 

What flash are you running?

 

You know I've noticed a similar feeling in tight corners but I attribute it to my RSB not moving as freely as i would like it to. Im not sure who recommended this but I plan to pick up some teflon tape for my RSB and hope that smooths things out. But hey maybe it is the ACD and not my bar?

 

Doh, reading comprehension fail.

I would venture to guess it's not the flash in this case or there would have been quite a few people sharing a similar experience.

 

interesting discussion - rear diff is just for on power more or less vs. steady state, where the ACD can have some influence. in general for steady state I think you gotta rely on good old fashioned mechanical suspension. Anyway rear springs need to be higher because of the Evo's motion ratio in the rear

 

The TRE max lock in my car improved steady state and in power rotation. The English Racing ACD flash had a profound effect on off throttle rotation, and also helped a decent amount with steady state and on throttle. I'm working with Aaron to solve some under steer it induced when I pick the throttle up and the turbo isn't spooled. It only does if I go straight to WOT, if I roll into the throttle it doesn't do it. Aaron is confident we can iron it out.

 

interesting what you mentioned - similar drivetrain setup here - ER ACD tune, and Cusco 1.5way done up by TRE

 

I'd be willing to bet its more of a bushing issue. I've felt shudders before on my BMW during braking and some turns and it was because the front control arm bushings were beyond shot. The control arms were literally banging inside of its worn out bushing.

What do you have for aftermarket bushings? Engine? Transmission? driveshaft? diff? control arms?