Track Day 27 + 28 -- Thunderhill East Cyclone

Going into this track day I was mostly looking to confirm that my DIY chassis mounted wing yields an improvement in handling that will hopefully equate to better lap times than the last time I was at the track. The track weekend though was also a present to myself, as this track weekend will be occuring the day after my 40th birthday! That said... a few small tasks turned into a bunch of stuff... so much for keeping it simple and just sending it! Overall though it was a success and I had really positive results from my modifications!

Modifications, Maintenance & Thoughts Before the Track Day.

Everything seemed to hold up pretty good from the last track day so there weren't any critically outstanding issues. There's a few standard items and then one stretch goal I may or may not get around to.

Swapped out spring rates on the Corvette

So as part of upgrading aero on my car and discussing the handling with a variety of other folks out there, it became apparent I was running too low of a spring rate. I spoke with the folks over at Eaton Motorsports again and they were able to order up some Eibach springs for me in the right size and in spring rates of 700 front, 750 rear. This should upgrade handling overall and help me keep a car with balanced handling to a potential hair of oversteer. We'll see how i like the car driving with these new spring rates and I'll report back on it all.

Testing out EBC SR11 Brake pads

While the Carbotech XP-10 brake pads treated me quite good at the track, lasting 9 track days and providing excellent braking characteristics, the new EBC SR11 brake pads are currently all the rage for performance AND durability. So I grabbed a pair to test out. Per EBC reccomendations I scuffed up the current rotors significantly to help remove material from the old pads and to help the new pads bed in quicker. We'll see how these hold up!

Added DIY Splitter Ramps to the 9LR Splitter & Confirmed Hardware

So you can read all about the DIY splitter ramps over in my 9LR Splitter article, but the short version is after researching various splitter ramp options ranging from $150-200... I decided to just make my own. We'll see if they hold up at the track. The good news is they're fairly reasonable to remove, but I'm fairly confident they should be able to do the trick. This should yield a modest bump in downforce on the front of the car, which may help with that bit of understeer I've been dealing with. It's also worth mentioning I took the entire thing off to begin with as it felt a bit loose, but sure enough, it's all as secure as can be!

There was some concern about the MPI wheel bearing as both front wheels had developed some top to bottom play. I had play going into the previous track day, but decided to risk it. The play didn't change at all it would seem, but it is enough when moving the wheel there's a bit of a "clunk". I measured the distance out to be .026" with a feeler gauge, so that may not be enough to worry about. I let the folks at MPI know I was having this issue and we're still in communication about it. They understandably can't see it themselves, so I took the measurement above and sent them a video of the clunking. They got back to me and are sending me two new front wheel bearings and will be taking these two back to take a look at. Hopefully the issue was just a fluke, and if not even more hopeful that they will continue to refine the product to be more robust.

Improved Airflow throughout the car

So what started as plan for a few small airflow improvements turned into a whole bunch of small modifications that were quickly adding up to a ton of notes. I decided to write about all of my C5 Corvette DIY airflow projects in it's own article. The short version though is I focused on improving airflow to and through the radiator, along with diverting a little bit extra fresh air up to the cold air intake air filters.

I swapped two of the rear tires out for some extras I had around.

So back on track Day 20 I picked up a nail through one of my tires that couldn't really be properly fixed. I got a whole new set of 4 tires, chucked the one bad tire, and kept the other three around just incase. Well, turns out I needed them as my rear tires were positively roasted after my last track day. They perhaps had one, maybe two track days left in them... but given I had a set of tires around with 2-3 days left in them I figured I'd swap those two in and keep the other two around as spares just incase.

How The Track Day Actually Went

With all of the last few details buttoned up and a track full of tons of gear, we made the 8 hour drive down to Thunderhill. We stayed in the nearby town of Willows CA, which has a nice little airbnb/hotel that is decent enough to stay at.

Saturday was about the usual scene for a winter track day. Colder temperatures were present along with a constant breeze. Still though, not too bad overall. This particular group was a Shelby club, so it was loaded with a wide variety of mustangs. It was interesting to see how my 25 year old Corvette stacked up against far newer cars. I'm glad to report back that it held up well, catching all the other Mustangs even with lots of aero in all of the turns. Unfortuantely, the straights were the issue. More on that to be written on the post event writeup.

One bummer for me going into the track day is that we were running the "Cyclone", which was a bummer simply because I wanted to compare my times this weekend to the previous time here without the wing on the car.

The refined aero and stiffer springs felt great and were far more confidence inspiring entering high speed turns. In mid speed turns the wing still helped a bunch, which combined with my willingness to rotate a car at 80mph being greater than 112mph balanced itself out nicely.

One big standout was the EBC SR11 brake pads. They had way better initial bite and feel than the Carbotech XP-10's, and held up to heat way better throughout the course of a day. It's not entirely fair to compare these brake pads as the XP-10s are streetable, and in my opinion the SR11's are not. Still though, what an improvement in being able to brake far better than ever! With that initial strong bite I could also heel toe / sidefoot far easier. Overall, a big improvement to the car! I'll be curious to see how they hold up!

Engine Temperatures were excellent as the DIY cooling mods clearly worked! I never exceeded 243 degrees fareinheight all day when previously even with colder weather I'd push well into the high 250s. I also only pushed above 240 after many back to back all out laps, where as normal lapping, especially in traffic, stayed at 237. So, I'm pretty confident the engine cooling modifications must all be working, though since I did them all at once I can't really point to any specific one as being superior to the other.

On Saturday I put down a best time of 2:06.310. I felt pretty good about that, but knew I was leaving time on the table in a few places. It's one of those things were small hesitations here or there can cost a good chunk of time. Brake just a few MPH more than nescessary from 120 down, give up a tenth of a second. Don't launch it into turn 3? There goes some time. Overly square up the cyclone hill? Throw away another tenth.

Sunday afternoon I really picked up some time on my laps though. I was chasing a far higher horsepower Mustang than mine and gaining on them every lap despite their near 33% higher power. Then, in a a subsequent session I put down two back to back 2:05 laps, with my best being 2:05.036 per timing the lap from video. 10hz GPS bluetooth track addicts has it at 2:05.307, so right around that time. I'm stoked though as I was able to drop a full second from Saturday. What was interesting was comparing daytime temperatures, wind, and when in my sessions my time dropped. Since Sunday was just a bit hotter and less windy in the AM, track temperatures were up a bit as were car temperatures. I saw a peak oil temperature of 243 degrees, which was a surefire indicator I was pushing faster lap times... but I also was starting to slide the car more as the tires got hot. Now normally, I'm told sliding is slow... but for me being able to rotate the car into a lot of the turns definitely helped me pick up time. While in some places it surely lost time as I'd understeer and push a bit wider than intended and have to saw the steering wheel to regain traction, but in other places I could pitch the car sideways a bit early while braking so when I entered the turn I'd already have the car rotated a bit. Not only was that fun, but apparently it was fast!

Other minor observation from out there at the track day was that leaving turn 11 I was always faster if I stayed in 3rd versus 2nd. While I had way more acceleration out of the turn in 2nd, it was really easy to accidentally step the rear out more than intended, and the time lost making the shift was notable. Every single time I stayed in 3rd and pulled through that section I'd be shifting to 4th right at the exit cone for turn 13. If I grabbed second, I'd always be shifting to 4th afterwards.

Another place I'd carry a lot more speed was going into turn 1 and just staying in 4th. If I downshifted to 3rd I'd have more drive into turn 2, but I had plenty of drive in 4th and the addition of a shift into that braking zone unsettled the car just that little bit extra and resulted in me shedding extra speed.

To get a lot of faster I think I need to get better at looking at session data and being able to compare lap times when trying different lines or gear selections. For example I tried two variations of the Cyclone, and in those variations were also gear variation. I settled on a line a friend showed me and staying in 3rd gear as I'd hit turn 6 just as quick... but perhaps that was just a matter of perception, as a tenth of a second isn't much of a difference at all!

Aero and Track Time Comparison

So, in the absence of being able to directly compare lap times, what can I compare from Thunderhill visit pre and post aero? Well the best I can figure is top speed on straightaways and cornering speeds.

Here are my three best laps from 2023 without a wing and splitter diffusers:

Here are my 3 best Laps from 2024 with a wing and splitter diffusers:

Section top Speed Comparison:

(Note: Pre is from before the aero modifications, post is after the aero modificaitons)

Front straight top speed:
123-125-122.4 - AVG: 123.4mph
POST:  123.7-120.4-121.9 - AVG: 122mph

As far as the front straight is concerned, I was down a bit on speed, but not much. My guestimation from these numbers is that the wing and the 9 degrees or so of angle of attack I am running largely matches the drag level of the lexan spoiler I had before so... no difference really. In theory if I'm exiting turn 15 faster due to the extra downforce then I am being affected by the drag but... I'm not willing to nerd that far out just yet on this data!

Turn 1 speed:
83.2 - 78.5 - 78.2 - AVG: 79.96
POST:  85.2 - 85.2 - 87.2 - AVG: 85.866

When it comes to cornering speed into turn 1, I was up 6mph on average. That's a prettyy significant gain, and in the car the difference was significant, especially the stability braking later into turn 1. Looking at how deep I carried speed braking into turn 1 would be interesting! I think I can safely say a difference was made here both in improved braking and downforce gain.

Turn 2 speed:
PRE: 70 - 69.7 - 68.4 - AVG: 69.366mph
POST: 70.1 - 70.4 - 69.1 - AVG: 69.866mph

Turn 2 did not yield as much of a difference as you'd think, averaging only a half MPH difference. It honestly didn't feel a lot different mid turn, and the numbers reflect that. Not sure why... but the difference here was insignificant, and I was pushing it every single time to near tha max. Braking into the turn sure felt better though and was at least more confidence inspiring. I'll take that, even if it might just be confirmation bias.

Turn 8 Speed:
PRE: 98.2 - 97 - 94.1 - AVG: 96.433
POST: 93.2 - 97.8 - 95.7 - AVG: 95.566

So I wanted to compare speeds here to see if I was any faster through this turn as it's a very high speed turn. Turns out... no... no I wasn't. Infact, I'm slower! I'm guessing willingness to fully send it on this turn played a big part in things. The difference of just under 1mph on average I'm not terribly willing to read into, but I was thinking perhaps I'd have a bit extra grip here and maybe see it in the numbers. Turns out that was not infact the case! Perhaps I'm just at the limit of these tires regardless of downforce?

Turn 9 Entry Speed:
PRE: 69.2 - 64.7 - 60.2 - AVG: 64.7mph
POST: 67.4 - 68 - 65.7 - AVG: 67.03mph

Turn 9 was a turn I wanted to really see about a speed difference on as I felt I was able to really charge that hill and gain a lot of time on people, and sure enough the numbers do bear a difference there of 2.3mph or so. Not insignificant, but not a strong gain like the turn 1 speed.

Back Straight Top Speed:
PRE: 109.5 - 105.2 - 110.1 - AVG: 108.26
POST: 113.1 - 112.1- 113 - AVG: 112.7

Well in a strange turn of events my back straight speed was up 4mph on average. I feel confident saying it wasn't because of my superior line choice either as I'd often be a bit off line as I'd overcook that last turn. Perhaps it's the extra aero hold through turns 10-13 meaning I hit the straight with a higher top speed? OR... perhaps it's because I stopped grabbing 2nd and just went with third. Yeah... it's probably that.

CONCLUSION: I can't really ascertain massive gains here, and this is just looking at a single metric which is peak speed, not peak speed over time which equates to lap times. Some gains can also clearly be related to a change in technique (pulling 3rd vs going to 2nd when going through turn 12). Overall. I can't say for certain the wing put me way ahead of the previous times, but overall it seems based on a few sample areas I was in general traveling faster with the new aero and brakes... so there's a probable correlation.