Track Day 15 - Buttonwillow CW1 with PCA - 315/30R18 Falken 615s - LS7 Clutch + Aluminum Flywheel

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For the 15th track day, we were headed to Buttonwillow CA. I haven't been at this track since my third track day, and I've had a ton of modifications and seat time since then. I was definitely looking forward to seeing how the car handled!

Modifications going into this track day

So after my last two track days, my torque tube bushings definitely had given up the ghost.

Incase the picture doesn't make it abundantly clear, my torque tube bushing had ENTIRELY disintegrated. Thus when I'd go from on to off throttle I'd get a bunch of clunking. Now, I knew this was on it's way out two track days ago... but still jammed another track day in as I had a friend in town and was excited. I shouldn't have, but I did... and such is life.

So I had the torque tube rebuilt and the bushings replaced, and I got a new clutch and flywheel. I went with an Aluminum flywheel and the LS7 clutch. This should give me a clutch that can handle far more abuse than my stock LS1 can dish out, and the aluminum flywheel weight should free up some rotational mass in the drivetrain for additional power. Party on!

Other modifications are the tires along with the suspension alignment and geometry.

So my tires were about 2-3 track days away from toast, and having discussed susension and handling a bunch with a variety of folks, were potentially contributing to some of my suspension headaches. pecifically, if you lower a C5 corvette too much without using drop spindles, you can find yourself pushing up against the intended geometry of the OEM suspension. I was not only lowered, but running 305/35R18 tires that are taller than stock, I had notably adjusted the suspension out of it's manufactured intended operating range.

The solution was four fold.

First, install a bump steer kit. I needed this offset rear bumpsteer setup anyways to help ensure I clear the coilovers, and I was hoping that I could get an alignment shop to tune out bumpsteer. I was wrong. I can't find anyone who will give me the time of day with configuring these, and I don't have the time or wherewithall to configure them myself. So I installed them with the baseline settings that mimic OEM as close as possible, and may someday in the future find somebody to help me out.

Second, step up to an esatablished 315/30R18 tire. I chose to go with Falken azenis rt615k+ tires in 315/30R18, mostly due to availability, but also due to positive reviews surrounding it as a track tire that has decent durability. I drive this car to and from track days and I'm trying to avoid sinking a fortune into this hobby so durability is key.

Another and key reason for selecting this tire was to both maximize tire width and thus rubber on the ground, and to get closer to OEM tire height. In doing so, I was able to raise the suspension to get the same effective height, helping return my suspension to it's manufacturer intended operating range.

Third, raise the car a bit to return to close to OEM geometry. It pains me to do this as the car has better aero lowered and it definitely LOOKS better, but I'm just fithing the OEM suspension geometry too much. Given I also can't get bump steer tuned into this setup... I'm just fighting the intended way this car should operate. Time to stop fighting it.

Long term I hope to get lowering spindles, which will drop the car 1" at the spindle, allowing me to keep OEM geometry.

Fourth and Last, adjust the alignment a bit. I was seeing too much inner tire temperatures with max camber up front of 2.8 degrees, so I eased off back down to 2.6 degrees up front. Every time I increased front camber I could see improved tire wear, but felt traction reduce a bit. I'm hoping 2.6 degrees will be more of a sweet spot for handling.

Oh and one last minor modification, I finally got the exhaust bypass put in place:

The OEM C5 Z06 Titanium exhaust is nice, especially as it saves 16lbs or so of weight... but it is QUIET. It's quiet to the point someone said my car sounds like an electric car out there on the track. Apparently a common modification to do to these is to add a little bypass pipe so some of the exhaust can skip the muffler. This works, and my car has a nice sound but is still nowhere near as loud as other cars. I still feel pretty confident I'd be able to pass most DB restrictions with it.

How the track day went

The track day began on the wrong foot before we even got going. I didn't sleep hardly at all for some unknown reason, and then when we got to the track we had a few hiccups with the NC Miata and tech. Fortuantely though it all came together pretty quickly, and the rest of the track day continued to turn right around into a most excellent track day.

My particular track group was "low intermediate" if you will, which is not normally the group I'd run in, but was placed there due to only having run this track once before. As expected, I was in traffic a decent amount, but it didn't bother me as much as I thought it would due to a fairly smart grid system. Plus once people figured out who I was and that I was running a much faster clip people generally let me pass pretty quickly. There was also one fellow who was able to run the same outright pace as me, and whenever they found me gaining on them they stepped their pace up, which helped give me that rabbit to chase so to speak.

I was able to put down several 2:10.253 laps, which in this particular configuration of Buttonwillow is pretty notable. From what I've heard, this layout with the star mazda turn adds about 8-10 seconds over the regular CW13 layout that most folks run here. That gives me hope of a sub 2 minute lap in the CW13 lap configuration, which is the litmus test for a lot of folks as to whether or not you're actually pretty fast. Given how fast running this at 2:10 in this configuration felt... it's gotta be pretty darn close! There were a few areas I was inconsistent and could pick some speed there, and definitely the final and first turn I was leaving some speed on the table.

I suppose it's worth mentioning my previous best here was 2:17 running CW13. I'm now at 2:10 running CW1. That would equate to at least a 25 second a lap gain I imagine? Not bad not bad. Also not exactly crazy given I've done a dozen track days since I was last here and have had made significant modications all around.

I had an exhaust Hanger fall off at the track

Not sure what caused it and who can be attributed to the failure, but one of my exhaust hangers fell off at the track. This resulted in my drivers side muffler clanging around a bunch while I was out on the track. My first effort to repair it with safety wire along failed, but a subsequent ghetto effort with a spanner wrench worked pretty good!

How the new Falken Azenis RT615K+ tires worked out at the track.

Part of me really liked the tires, part of me didn't like them.

The pros were:

  • The tire didn't grease out from heat as much or nearly as early into my sessions as the Federal 595 RS RRs. This in turn let me push the car longer and harder, which aligns much better with the goals of this track car to be able to run a strong clip for full sessions without having to back off.
  • Traction was definitely superior and I feel contributed to me being able to push the card harder.
  • Slides were controllable and easy to recover from.

The cons were:

  • Almost no auditory feedback at the limits. My federal 595RS RRs would start to screech as they heated up, and would definitely screech once they were hot and sliding. Even when these Falken 615s were starting to overheat and slide they were silent.
  • Tire wire shows notable feathering (like the edges of serated knife). Not sure if this means I need more camber in the front but I'm already at -2.6 degrees?

How the Car did overall with the upgrades and changes:

The new clutch and flywheel seemed to work pretty darn good. Shifting was reasonable, clutch work was good, and rev matching was straight forward enough with sidefooting (note: I want to lead a movement to stop calling it heel toe anymore). I believe the lighter weight flywheel freed up a bit of power which was nice. The lower height tires also likely altered the final drive ratio in such a way that I had more torque as well. I would be just shy of the rev limiter in 4th coming into the high speed turns so I think I'm geared perfectly for this track.

Oil cooler continues to kick ass! I saw a peak temperature of 243 degrees. This is down from my all time peak here of 283 degrees, and I only hit 243 degrees after 25 minutes straight of some of my fastest laps yet at a much faster pace than what resulted in my 283 degree temperatures from before. Needless to say, and oil cooler works wonders for helping stay cool!

Chassis felt solid overall. I was still getting some squirm from the rear end at high speeds. Not sure what is to be done about it. The far fancier porsche I was chasing around the track also had the same squirm/wiggle in high speed turns so... maybe it's just a thing?

New Exhaust Sounded GREAT! I was abit skeptical of it as it honestly sounded quite lackluster when lugging around on the highway in sixth gear. Wide open throttle though above 3k this car sounds GREAT! It's honestly confidence inspiring in a way. It sounds like it's hungry, and it wants to eat porsches damnit! LET'S GET EM!

Bucket seat and harness felt pretty darn good as well. Nothing new to report really, just they sure do the job nice, and I don't even mind my HANS device all that much.

I was struggling with popping out of first gear and definitely popping out of reverse. I'm quite confident the dudes working on this setup did not align the shifter correct, which given they didn't have the alignment tool makes perfect sense. I'll re-align my shifter and hope the car goes back to being happy.

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