Track Day 11- Streets of Willow CW - Delrin Bushings

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The time between these last few track days was quite significant, clocking in at over 30 days. I generally am trying to run at least a track day a month, so this was quite the gap from that goal. However California was having a ton of rainy weather, which when combined with the Holidays meant that I had a large gap to tackle a project on the C5 I'd long been neglecting, installing Delrin bushings from Borg Motorsports.

Bushings are often named as one of the most critical upgrades to do first on your C5 for handling. The OEM rubber bushings are quite soft for comfort, and in many of these cars are over 20 years old. My 1999 C5 definitely qualified for the 20+ years old and worn out category. As you can probably tell from the timeline of my posts though, I did not upgrade the bushings right away. The job was daunting for the home mechanic. I would come to discover through some research though that doing the job yourself with Delrin wasn't all that crazy.

Installing the bushings isn't all that impossible of a task. It was mostly time consuming as I had to tackle taking apart all 4 corners of the corvette quite notably, faff around with cutting and pressing the old bushings out, and then reassemble. I was able to press the bearings out using a bench vise and two appropriately sized and quite large sockets. You can buy the same giant set I used from harbor freight for about $75 or so.  It's worth noting getting the new delrin bushings back in is a breeze, but at no point should you resort to a hammer. Having the full torque sheet for the c5 on hand really helped expedite the process as well.

Check out the installation video that Borg put together on how to make this work as a garage mechanic:

Another issue that occured was removing one of my OEM camber bolts, the plate was clearly damaged. Since I needed to get new camber bolts, instead of spend money on replacing OEM I decided to pony up for the AMT Motorsports Camber Kit. This will ensure that whatever setting I have put in place is locked in and can be relied on.

Once I had the entire car together I went for a test ride, then got the car aligned and re-torqued everything.

With all of these in place, I went back to my alignment guy and went for the following numbers

Ride Height3.75"4.25"

Please note that these were the numbers I was running relatively effectively before with my OEM rubber bushings, along with matching up with the Pfadt reccomendations for a dedicated track car with street tires. I also have my article on alignment specs you should reference.

Spoiler alert: I cannot recommend running these numbers at this time based on the tire temperatures I got coming off the track and tire wear I was seeing coming off the track, even at a fairly turn intensive track.

How it went at the Track

The day started pretty rough. The wind picked up around 4am and only slowed for a brief period of time around 11am. With cold temperatures and the constant 16+ mph winds, the track temperatures never really came up that high, and as per usual on a cold track day there were a lot of interesting spins and off track excursions. While I kept it on track the entire day, there were a few times I got quite loose and had to recover. The looser conditions also made for some fun, as I would sometimes take a lap and practice off throttle over steer to bring my car around a turn better.

The Delrin bushings proved to yield some significant improvements however at the track. On the least wind and best temperature session of the day (around 11am) I was consistently running 1:28 laps (my former best time) and then clicked off two 1:27 laps, with my best one coming in at 1:27.24. This meant about another second improvement in my time, with more on the table I imagine with better temperatures.

Finally using my tire temperature tool:

As so much was going well on the Corvette, I could finally start to focus on ancillary tasks instead of trying to troubleshoot significant problems. So after a session I came off the track and instead of taking my usual cooldown trip up and down the back hill at the end of the pits, I went straight to pit and used my JOES racing tyre Pyrometer to grab temperatures. Here's the temperatures I saw


57c - 134.6
55c - 131
51c -  123.8

52 - 125.6
46.5 - 115.7
42 - 107.6


59 - 138.2
55 - 131
53.5 -128.3

53.7 - 128.66
48 - 118.4
43.5 - 110.3

Please not tire temperatures all go from inside to outside. Cooler temps on the passenger side reflect that this direction has the drivers side mostly taking the brunt of the heavy corner as this is a clockwise direction.

What does this mean exactly? Well I'm seeing a drop accross the tire in temperature from outside to inside, which isn't exactly crazy but could indicate that reducing camber would yield a more balanced usage of the tire. Given how cornering heavy streets of willow is I think I can safely reduce camber here and have a setup that will more than exceed the needs of any other track I am likely to take the car on.

I'm going to verify this information with the community, but I think I can safely drop the front to -2.6, and the rear to -1.4. More information to come on this.

How did other aspects of the car hold up:

So given there's a lot of modificaitons in here, here's the general take on how other things went.

The Cadillac brembo brakes remain excellent. No brake fade, no issues, and easy pedal actuation that allows me to acheive full braking while still having ankle articulation to heel/toe shift into the correct gears.

The Harnesses help, but I still feel less than planted: I'm starting to learn to trust the harnesses more, but I find I am still often bracing against the side of the car with my arms or legs, which in turn reduces their ability to fully articulate the steering wheel or pedals. I'm not fiding it holding me back from anything at the moment, but it's surely not ideal. I believe a bucket seat is in short order for this car.

Personal takeaways for areas of improvement:

I continue to need to improve my hands on the steering wheel and shifter. I continue to leave my hands on the shifter when not nescessary, driving for prolonged periods with one hand. The more I reflected on it at the last track session the less I felt I needed two hands, and two hands even felt slower to steer than one hand... but this is supposedly very much not what I'm supposed to be doing.

One big are of improvement that really helped is as I got more comfortable with the car and the track, I started to look much further ahead. This yielded significantly smoother driving, and it helped me get on the throttle sooner as I knew I was aiming in the ballpark direciton I wanted. At times this was difficult as the HANS device I have restricts helmet movement to a certain degree, but overall I found it helpful to look much further ahead than I normally would.

Next steps for the C5 Corvette:

There isn't much time between here and my next track day, so I will likely just get the alignment adjusted again to pull a bit of camber back out of the car.

I'd love to finish the Accusump and oil cooler, as I was still seeing 270 degree oil temperatures on my fastest laps at the track despite the very cool air tempatures. Time will likely not allow however.

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