Thread: Street Mod.
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Old 08-07-2017, 11:16 PM   #1820
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Member#: 80649
Join Date: Jan 2005
Chapter/Region: South East
Location: Columbia, SC
2000 2.5 Auto-X RSTi


Originally Posted by speedyHAM View Post
Most of my handling problems stemmed from the lockup of the front diff coming out of corners causing push. It was good on entry and good mid corner, but corner exit I was losing time. A torsen with proper suspension tuning to take advantage of it would help pull the car out of corners instead of causing push, leading to higher lateral acceleration throughout the corner.

I see a center DCCD as a band-aid in biasing torque to the rear wheels to counter the understeer being caused by the front diff locking up under acceleration. Ultimately the torsen and a DCCD with a great controller would be best.

Ultimate lateral acceleration will happen when the tires that are the most loaded are at their optimal slip angle. Locking the front end under acceleration means the inside front will never be even close to it's optimal slip angle.

This is my theory, I hope I get to test it.
I get your theory, but I think you're missing the point that a 1 way clutch pack diff can be tuned to work better than a torsen and not cause the front to ever understeer. You're also missing how much the rear diff plays into power on understeer.

The DCCD isn't a bandaid at all, it's a useful device that lets you dial in the balance of the car on power. What you're missing by not having it is the ability to have an actual, true 50:50 split. The viscous center will ALWAYS spin the front up first, which is why you're having so many issues with locking the front first. It's getting all the torque, and only after it gets it does the center viscous start to lock and send power rearward. I have videos from when I had a viscous center that show on hard launches the front wheels spinning up first and then the rears following suit a few tenths later. The great thing about the DCCD is you get 50:50, but you also can get rear bias for when you want rotation as well.

Yes, text book ultimate lateral acceleration will happen at the optimal slip angle at all four wheels. Assuming you can actually get that to happen on a production car, you know the optimal slip angle from the manufacturer, and continually reset your car for whatever surface and temperature you encounter... That almost never occurs in autox though. I use a race capture hooked into solo storm to measure the G values. If a change makes those values go up in steady state, that's good. If it doesn't or it goes down, I undo it. I can say that in my testing, trying to keep the wheels down does not result in higher G values, and in most cases is detrimental to how fast the car is through corners. Allowing the car to move (assuming fixed camber curves, etc) provides higher peak and sustained lateral G values. Using DCCD with a good controller and clutch pack diffs maintains or improves longitudinal values as well.

However, if you're able to make your theory work, then cool I've been told many times I was wrong so I'm not going to tell you that. I'm just going to suggest I've seen others try and not succeed using a gear type front.
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