Preface:
Ex-race car driver/engineer
HPDE track instructor
Overall Track Junky
Months of negligence and procrastination has finally come to an end. The ex- world’s most elaborate (and sulfur reeking) paper weight has finally been utilized for its intended purpose. Behold, the ATS carbon clutch-type Limited Slip Differential … in its fully operational state and tested at the circuit of Laguna Seca this past weekend.
This unit was purchased from my good friend Sharif at Forgedinternals.com sometime back in September of last year. Not until recently, it has been sitting on the workbench in my garage. *embarrassed* Blame it on my busy schedule which ate into my track play times. The urgency was felt again when Speedventures (
www.speedventures.net), the club I go through for my adrenaline fix, managed to secure a date at Laguna Seca with little advance notice. Normally I’d take on the full installation myself, because I’m the best mechanic I personally trust (aside from a very limited few whom I’ve worked with and have an understanding with), but I did not have the time to spare. After much debate, I left the car off at Street Image (
www.streetimage.com) before taking off for a 4-day snowboarding vacation at Lake Tahoe.
After the install the typical clutch-type LSD break-in procedure was carried out. It involved doing low speed (15-20 mph) 2nd gear figure-8 maneuvers in an unobstructed open lot for approx. 20 min. – optimizing virgin clutches’ disc-to-disc interactions and conformities. After the session, the differential fluid is drained and replenished. While ATS recommends the outrageously expensive ATS specific gear oil @ $100 per 4 quarts (!), I was told by ATS USA unofficially those were not necessary (shhhhhh ... you didn't hear that from me!) – any differential oil should work satisfactory, although some better than the others. I elected to refill using the Shell Spirax S 75W90 synthetic gear oil I have on hand. No friction modifier additives were added, nor did I feel the need for it at Laguna Seca.
I may try Redline gear oil next solely as a point of reference.
On the street, the ATS exhibited virtually zero clicking or grinding noises that one would normally expect of some metal clutch-type LSD. Its operation was seamless and discreet 90% of the time (when the LSD effect isn’t being utilized). The only sign of something special back there was the tail-tail ‘tut tut’ of the inside rubber skipping as the LSD attempts to bind the rear-axle under load while making excessively sharp turns from a stop or low speed (i.e. pulling out of a sidewalk ramp merging onto a street from a stop). Didn’t bug me much - No biggie at all!
On the circuit of Laguna Seca I was able to sample the ATS at maximum duty cycle and beyond - it impressed. In the past, the oem viscous unit proved vastly inadequate for track duty both from a performance and driver confidence stance. The single largest shortcoming of the viscous unit is the prerequisite wheel spin (lost of traction) before the LSD effect is generated. The secondary is the very low torque handling capacity (ability to bind the axle) - somewhere around 33% when new. The combination is excessive rear-end waggle and shaking of the laffy-taffy when hustling around the corners too eagerly. Not at all confidence inspiring if you weren’t use to it. Remember a large part of racing is also mental. Got Ballz? It is however manageable by an experienced driver (those power-on oversteer are fun to catch!), but certainly not the fastest way around the turn!
The ATS was again seamless in its operation on the track. The (LSD) clutch engagements were fluid and progressive as advertised. I didn’t notice sudden jerks or disruption of power – like butter. The ATS means business once it engages. The locking of the rear axle induces a yaw resisting nature (less likely to snap oversteer and decreases steering input sensitivity), that equates to a solid and planted vehicle while boosting driver confidence exponentially – exactly how a LSD should work. For an experienced driver this makes the following possible: Late apex slightly, aim, get on her early and hard, shoot out of the hole with more speed than ever. I was having so much fun I couldn’t stop screaming (as you’ll all see in the video(s) to come later).
The only unknown at this point is the durability for the clutch plates. Only time well tell.
Thumbs way up for the ATS carbon LSD.
-Clint
ATS carbon LSD @ Laguna Seca impression.
