Back on track, this time at the Thunderhill 5 mile course (w Crows Nest). The car ran like a champ!
There were appr 20 changes done to the car since the previous shakedown I did in February, therefore this was more or less a new shakedown, with a bit more confidence since I've been able to put some street miles on the car these last months. The main performance changes were the installation of aero parts, swaybars and different coilovers/springs, plus much needed Borg delrin offset bushings for the front LCAs.
- The math worked out right wrt to swaybar wheel rates, the balance was pretty much perfect, as it was on the initial shakedown without the bars. Same exquisite agility, just a lot less roll now which is awesome!
For a GTM doing only track duty only I would increase the spring rates to make it act like a racecar but the current rates are a good blend for street/track. A firm ride on the street but acceptable. If you have adjustable shocks you can cheat a little bit and firm them up a little when on track to keep the mass in check during transitions.
Room for upgrades:
- This is almost silly but turned out to be the main gripe: I need to remove the driver door armrest! It kept limiting my left arm downward movement when turning left. Also limits quick oversteer corrections when turning right. It was a bit like driving one handed. That's never ideal, especially without any powersteering to muscle the 305 wide front tires. It wasn't as bad the way I sat before, but in the week leading up to this track day I bought a Kirkey seat which bolted lower on the floor with more layback. In total that was a huge relief to get full helmet clearance being 6'3", but obviously it resulted in the armrest needing to go as well. Oh well, easy one.
- G50 rear rubber mount needs help. The transaxle moves too much left and right during cornering, making it difficult to get to the correct shift gate with confidence (3rd/4th gate vs 5th/6th gate for example). I think some kind of clamp to keep it fixed at the track, but removable to just have the rubber mount for street, is the answer.
- The rear diffuser angle is still too steep for my liking. Going to work more on that to reduce drag and add downforce.
Other notes worth mention: The car pulled some pretty impressive lateral Gs already after a few steps of shock absorber tuning, so luckily the oil pan baffles from Improved Racing kept their promise. The oil pressure stayed steady in the mid to high 30s up to around 1.4G. When I ran with sustained (~5 seconds) cornering force higher than that, the oil pressure went as low as 26psi but it still held steady there. Thankfully never ran dry...
Speaking about the motor, the LS1 does good work but a GTM on good shocks can definitely handle a lot more, as many GTM builders have already proven. Doing something about that soon.
Although I was basically driving one handed, and still working on small setup changes as I ramp up the level of attack, times were good. The AiM logger started at 3.14, then along with shock adjustments 3.12 on repeat, then 3.10,5 and then 3.10,2 in bad traffic (solid 3.08 without traffic). This step by step grip and detailed handling improvement by gradual changes to the shock settings kept going on even as the ambient tempartures progressed from mid 70s up to 97 degrees.
Bottom line, a GTM is a quick animal when done right. Can't wait to go fine tune some more, get that arm rest taken care of and hit the track on a cool day.
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