The weekend started with a trip to Chicago late Thursday night; en-route to an 8am Appt at AMS Performance for some upgrades. Waiting at the shop was an upgraded 12 plate rear diff from Shep racing! I have been awaiting this for weeks, as I’m sooo sick of mid-corner understeer in the car. Also planned was an AMS Moustache Bar Eliminator to further reduce unneeded weight and improve shifting. As usual, everything at AMS went like clockwork, it’s so nice to have confidence in a shop! More on the changes later.
Rain overnight and into Sat provided wet track conditions until about noon. I personally love driving the Evo on track in the rain and knew it’d be a great way to get used to the new Shep rear diff. I also was debuting new front Girodisc 2-peice rotors and Raybestos ST43 pads all around.
I did 2 sessions in the wet, both with Dunlops on (I planned ahead) and had a freakin ball! The first thing you’ll notice is the diff creaks at low speeds if you are turning tight. If I hadn’t read this on previous reviews, I would have been worried too! Along with that, the AMS Moustache Bar Eliminator added a bit of noise from shifts into the cabin area (my car is mostly stripped) but I really grew to like the feedback. I thought the shifts seemed faster and more crisp personally.
Back to the Shep Diff – If you’ve read any of the reviews or claims about Shep’s rear diff, they are all true. It allows you the ability to finally create throttle-on oversteer but in a very controlled and predictable manner. Nothing snap or scary by any means. Before in the wet I could force it sideways but all the diffs/electronics would correct things. Whereas now I could pitch it and it’d carry that skid until the wheelspin caught up and it’d power out of the corner. If you’ve owned an STi and rolled back the DCCD; you know what I mean here. I’ll splice up some vid later of the wet stuff.
Around lunchtime things started drying and I mounted up the Hoosiers. Since I was playing in the rain I had the #2 gridspot and stayed up front (and out of traffic) all weekend which was nice. Alot of the Vettes and such stayed in the pits so they had to work from the back of the 40 car TT field!
I was a bit cautious in the first dry session to warm up the tires and really see what this rear diff would do in dry conditions. The ST43 pads were definitely different, they definitely took longer to heat up as compared to the Hawk DTC60’s I have been running and also squealed like all he11 for a good 2-3 laps. Once they were warm it seemed they needed far less pedal pressure to stop. This took some getting used to throughout the weekend. Rear diff reacted very predictably and I had some slight oversteer in several of the turns, enough that I had to countersteer a bit. I loved it! I ran a 1:35.2 which equaled my personal best from the July event. The next session I let things fly and set a new TTA track record with a 1:33.9. That also put me in 1st of 8 cars in class. Vid below.
Absolutely perfect day. However, I had a slight incident the night before when my jack rolled while rotating tires. No real damage other than some scratched paint – I thought. In the practice session the car wouldn’t go past 3k w/o sputtering, which I assumed meant an intercooler pipe was bent or popped. Turns out I bent the inlet on the intercooler and the coupler obviously wasn’t tight. So I bandaided that as best I could and went out in the next session just to put a time down. Ran a 1:35.6 which put me in 1st by just .1. The next session I let things fly again and broke my TTA record from the previous day – 1:33.1. That landed me 1st of 6 in class. Vid below.
Along with the new TTA track record, I set a personal best by nearly 2 seconds. I did this with rear tires that had 22 heatcycles by the end of the weekend! The ambient temps were great, but with newer tires there’s definitely more left in the car. Overall, the transition from TTB -> TTA (where I get 19 more ‘mod’ pts) is progressing. I plan to ‘max’ the car out for TTA next year and make a good hard run!
Huge props to John Sheppard for an awesome rear diff. If I weren’t maxxed out previously in TTB ‘mod’ points I would have had this long ago! I would have really liked to have it when I ran Redline Street here as the understeer was even more troublesome on street tires. Thx to AMS for the install and great/safe tune as always. Thx to Martin @ Girodisc for talking me through both the rotor purchase and especially the ST43 pad compound differences. Also thanks to AMSOIL & Hoosier.
Vids! I’m following 2 different cars, both TTU Z06 Vettes. Watch them pull away from me on the straights above 90mph! I ran nearly identical laptimes to each them however even though they are still 2 classes above me!
Vid from Saturday: (spliced from 2 different sessions)
Vid from Sunday:
2nd lap is my fastest of the weekend