Quaife LSD maybe not such a good option?

[bstuke]

Hindsight and I put a Quaife LSD in the 818R late last year. Since then the car has developed a pretty good push on throttle.

I am wondering if the Quaife is too tight to be used in a rear drive push config instead of a front drive pull config.

I competed in a skidpad challenge Sunday and was .5G worse than last year, and ended up losing to two Exocets. I beat them soundly last year.

I have been fighting the push quite a bit, and happy for any feedback.

No sway bar, Koni's set full minimum.

[UnhipPopano]

Taking a WAG, the LSD has increased the amount of under-steer that your car has. for the competition you are trying to compete in, you probably want a more balanced car. The following may explain this better, but the two best options are to raise the rear ride height and/or use lighter springs in the front:

A driver plows their car when the car under-steers and the driver maintains the car in the under-steering condition.

Novice drivers occasionally plow their cars when they enter corners at too high of a speed, especially in street cars that are set up to under-steer. The car exceeds the grip limit of the front tires and starts to under-steer, the driver maintains steering angle, the result is a plowing car. Typically the difference between what the driver is asking from the car greatly exceeds what the car is capable of - the car is being visibly over driven. This type of plowing is not good, and instructors get the drivers to enter turns slower to eliminate it.

An advanced driver in a car set up to under-steer might experience under-steer on corner exit under power. Consider the choice between under-steer and over-steer in this situation:

An under-steering car gets to the outside edge of the pavement quicker but is accelerating the entire time. Such car loses some speed due to front tire scrub compared to a neutral car.
An over-steering car enters a drift and typically maintains the drift for as long as the driver is on throttle. While the car is in a drift it uses only a portion of its power to accelerate forward, with the rest being wasted by spinning rear tires.

A third option is to lift off the throttle entirely, which typically stops under-steer.
Neutral handling would be ideal, but realistically not always achievable. A drifting car exits corners with less speed than an under-steering car. A drifting car also spends more time in the corners due to being sideways. An under-steering car, when compared to a neutral car, loses some speed due to tire scrub, but generally an under-steering car will be quicker than an over-steering car. A car that is coasting because the driver lifted off throttle is similarly slower than an under-steering car under power.

Given the choice, then, the fastest option is to have a car that under-steers, hopefully not by much, and plow it out of the corner under power. The less the car plows, the faster it will be. Unwinding steering can make some cars not plow due to reduced lateral force demands and still permit these cars to fit into the track.

[bstuke]

Thanks for the feedback. I was actually contemplating doing both. Raising the rear a little and 50/100lbs off the front springs.

[UnhipPopano]

what is your Front Rear weight balance? and what springs are you using?

[Wayne Presley]

Roll axis. An line drawn through the front roll center to the rear roll center. Positive roll axis is front roll center lower than the rear.
Adding roll axis causes the car to turn in better due to more weight being transferred to the front tire. But it also hurts the drive off the corner. I would have set the car up different for the skid pad than for autocross or open track.

[bstuke]

Roll axis. An line drawn through the front roll center to the rear roll center. Positive roll axis is front roll center lower than the rear.
Adding roll axis causes the car to turn in better due to more weight being transferred to the front tire. But it also hurts the drive off the corner. I would have set the car up different for the skid pad than for autocross or open track.

Pretty bad push during AutoX as well.

[Zach34]

Anybody have any experience with the stock LSD in the STI 6-speed? Understeer much?

[Wayne Presley]

The STI came with an open, Suretrac or helical differential. I've driven the helical in the 818 and it worked well. My favorite type of diff fir autocross and open track.

[C.Plavan]

I had no issues with push on the track with my Modena unit (TBD Type). The TBD types are made for autocross. Much better than a friction plate LSD for autocrossing.
Disconnect the front sway bar if it is attached and ditch it. It's not needed.

[UnhipPopano]

Perhaps the better question to be asked is if any LSD is needed in the first place. If the car is able to corner without one at over 1 g, how much additional traction can be gained for use on a track where the object is not to be sliding around? A LSD should start to work when one wheel starts to spin. This is the same point where Traction control would apply and both systems in effect apply breaking of one wheel to transfer power. Also, a LSD that is set up for the front wheels should be looser that one for the rear wheels. If bstuke's LSD is engaging on his 818 before the outer rear wheel is actually slipping, it is not working as it should.

[Mitch Wright]

The handful of laps I have done with Bob and Michaels car with an open diff and around 200WHP I didn't notice wheel spin. NCM is a track with a lot of elevation change and place where the car gets unweighted at the apex or track is gone off camber.
Add 50 or 100hp it is possible to be more noticeable.

[Wayne Presley]

I have drive an R with and without a LSD, it needs one for sure.

[SixStar]

Have you corner balanced the car? What springs are you running?

FWIW I'm running the 300# front and 500# rear with a Modena TBD. When I had the springs reversed the car was undrivable, I was actually lifting a front tire on exit.

[wleehendrick]

I was actually lifting a front tire on exit.

Untitled-12.jpg

What's wrong with that?!?

[Mitch Wright]

I have a Cusco RS 1.5 2 way LDS, I have not driven the car on track at speed yet other than the 30 miles as a go-kart which was at 5/10 at best. I will say the felt good for being not close to sorted at least at 50% on stone age tires. I am looking forward to driving the with proper tires and aero and I am sure it will be a different animal.

[Thumper]

I was going to install the Quaife QDH3Y on my 818. Do you have experience with it on road course racing? How does it feel?

[Hindsight]

I have one in mine and it feels great on the track. Puts the power down very well coming out of the corners. No one-tire-fire. I can't compare it to before installing the limited slip though, because I never drove the car without it.

[RetroRacing]

We experienced STUPID power on understeer with 400lb front and 600lb rear, plus a one tire fire out of the corners with an open diff.

[RetroRacing]

We are installing 500lb front and 700lb rear for next test.

[Bob_n_Cincy]

We are installing 500lb front and 700lb rear for next test.

I had to install tender springs when I went to harder springs to prevent them from coming out of the spring seats.

Bob

[Thumper]

I'm actually selling my Quaife LSD since I've sold the 818. If anyone wants to check it out, it's in the classifieds.