996.2 LSD for autocross

[Number1_dog]

I have a 2002 Base 996.2 with M30 suspension and sport exhaust. I am an avid autocrosser, with 200 tread wear tires, with Metro NY PCA. When I brake before a cone, turn and get back on the throttle, the rear end wiggles and goes to one side. I assume this is due to the open diff, my SC did the same thing.

My mechanic recommended a guards LSD, don’t know if they make one for a base 6 speed? Are there any other LSD out they that people have experience with? If guards does have one for my car is that over kill?

Thanks dog

[roblav]

From my formula car days, the only reason for a LSD is if you're getting significant inside rear wheel spin. You can always decrease rake, soften rear springs or ARB, add rear toe-in, and/or add front toe-out before resorting to a LSD. But it's your money.

[Number1_dog]

I am willing to listen, I am not sure if you autocrossed your formula car, but it is my understanding that an open dif will load up the power to one wheel in a turn more than the other and I am running sticky tires. Most of our AX courses are run counter clockwise so there are a lot of left turns. So I am approaching a cone fast, brake, quickly turn left, then floor it, the rear end kicks to the right. The same thing happens in a quick right turn the rear end kicks to the left. It was my understanding that in an open dif the inside tire, the left tire in a left turn, had more power that the outside tire and was overpowering that tire and pushing the rear to the outside. I don’t get wheel spin, just a twitch to the outside and costing me a couple of tenths of a second.

[roblav]

It sounds like you're choking the corners... apexes are too early. As a general rule, late apexes are better. Try that technique first, get that right, then work on suspension, and the differential last.

[Matt Monson]

Hello,
While we definitely still manufacture an LSD for your application, it’s not what I would recommend. As you’ve described, in auto-x you rotate the car early and do actually want it a little on the loose side. The lock up under braking you get with an LSD will make the car harder to rotate.

For auto-x in a 911, what you really want is a TBD, torque biasing differential. We no longer make those, but of the two on the market I would strongly recommend the Quaife. The other one, by Wave-Trac has a proprietary gizmo that locks it like a spool under the brakes. They also seem to have more failures than the Quaife.

Regards,

Matt Monson
Guard Transmission llc.

[Number1_dog]

Matt thank you