"Mr. Toad" at Laguna Seca (August 2020)"Mr. Toad" at Laguna Seca (August 2020)
 Trying on new numbers |
 A foggy start to the day, with the usual pile of stuff that easily fits in a Mazdaspeed |
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Green placard: pre-session checklist Yellow placard: Freektune data-run checklist Manual gearshift: required on my cars |
 1993 Mazda RX7 repowered with a 2011 Chevrolet 6.2-liter V-8 |
The black car is especially clever as it is a BMW Clown Shoe; Pennywise was the name of the clown character in Stephen King's horror novel IT and the movie.
The white car is a BMW 325is with an M3 engine.
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Beyond being mindful of good health, my goal for the day was to explore engine upgrades I had added the previous week, including an improved Cobb air intake and engine-management tuning from Freektune. This combination was forecast to increase the stock 263 horsepower by 10-15%, or to 289-302 horsepower. My initial impression was not purely of more power but rather that the engine no longer struggled to reach its 6700-RPM redline, instead pulling strongly all the way to (and past) redline. On several occasions the tachometer showed ~7000 RPM though the rev-limiter didn't kick in and subsequent analysis of engine data showed a minimal transgression beyond redline.
My expectations were that the increased power would lead to a faster top speed on the front straight and Turn 1 leading to The Andretti Hairpin (Turn 2). Other areas such as between Turns 4 and 5 should also improve but quantifying them might not be quite as obvious. In any case, lap times should improve.
 Best lap of the day |
 108.4 mph in Turn 1! |
Top speed improved as expected, with a speed of 107.9 mph during the morning session and a blistering 108.4 mph in the first session after the lunch break. Alas, brake fade beging to appear mid-morning so for the most part speeds later in the day were slower though lap times improved. The followng table compares the best laps (by lap time) for this and my previous two visits to Laguna Seca. Three other notable laps from earlier in the day including the morning's fastest speed in Turn 1 (107.9 mph), and the next lap in that session with my best speed through Turn 2 (44.5 mph). The final lap in the table is the one with 108.4 mph in Turn 1. Alas, traffic later in the lap kept the lap time from being very good.
| Oct. 2019 |
Feb. 2020 |
Best Lap |
Fastest (am) Turn 1 |
Fastest Turn 2 |
Fastst Turn 1 |
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|---|---|---|---|---|---|---|
| Session | 7 | 7 | 7 | 2 | 2 | 4 |
| Lap | 4 | 7 | 8 | 5 | 6 | 4 |
| Lap Time | 1:59.280 | 1:56.723 | 1:55.850 | 1:56.961 | 1:56.283 | 2:00.481 |
| Turn 11 | 30.0 | 37.1 | 35.8 | 37.4 | 33.8 | 35.8 |
| Start/Finish | 91.4 | 88.3 | 88.6 | 89.4 | 88.0 | 90.3 |
| Turn 1 | 104.9 | 105.0 | 105.8 | 107.9 | 106.3 | 108.4 |
| Turn 2 (Andretti Hairpin) | 37.8 | 41.0 | 40.5 | 42.8 | 44.5 | 40.6 |
| (speeds in mph) | ||||||
During my February day at Laguna Seca I focused on exploring some recent brake upgrades. They performed exceedingly well, and the G-LOC pads still had 80% of their material left after 2.5 track days. My brake worries seemed to be history, though with increased power I was careful to monitor brake and tire temperatures along with tire pressure.
After the day's first session, front tire pressure was up 10 PSI (left) and 11 PSI (right) from the initial 36 PSI. I bled off most of the extra pressure. Temperatures measured with a borrowed pyrometer were elevated, consistent with the increased pressure, but not alarmingly so.
After the afternoon's first session, I again measured temperatures and was taken aback to be greeted with a cheerful "Hi" from the pyrometer in areas where nearby measurements suggested temeratures might exceed 500°F. The table below summarizes my measurements. As I was measuring temperatures I heard a metalic "plink" near the right front wheel and looked over to find two wheel weights on the ground (highlghted in the photograph to the right). Apparently the brake heat had melted the adhesive.
| tire | brake caliper | |
|---|---|---|
| left front | 162.2°F | Hi (>500°F?) |
| right front | 163.8°F | Hi (>500°F?) |
| right rear | 114.2°F | 284°F |
| left rear | 135.6°F | 278°F |
 Front brake pads |
 Front brake backing |
 Front brake pads on end |
A teardown of the brakes a few days later revealed that the front brake pads had been incinerated, despite G-LOC R12 pads being rated to 1015 C (1860°F). Starting from 80% of the pad material remaining, the outer pads were down to about 10%. The inner pads had a bit more remaining material but were cracked. (The photographs above show the pads from outer left to inner left, then inner right and outer right,) The asymmetrical wear between inner and outer pads is due to the single-piston design of the stock calipers.
Based on the data from the fastest Turn 1 run during the session
preceding the "plink," the energy the brakes had to dissipate between
Turn 1 and Turn 2 was around 1,600 kilojoules, roughly enough to boil
4,790 liters or 1,265 gallons of water from room temperature.
Something close to that was repeated every two minutes or less, not to
mention other braking areas which dissipated lesser (though still substantial)
amounts of energy.
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With a fresh set of Nitto NT05 tires after June's track day at Thunderhill my tires didn't have problems, but there seemed to be more tire junk kicked up by other cars than usual. The first photograph above shows a skid mark on my windshield from one of these chunks; the other two show similar chunks stuck on my front tires.
(This image is contrast-enhanced from the original photograph since the dirt stripes were thin and thus rather faint.)
At first I thought there might be some interesting physics behind this
pattern but after consulting with several of my physics teachers we
decided it's probably just an irregularity in the magnetic "meatball"
which is about 0.035" thick but tends to curl.
This video (QuickTime version) shows laps 1 through 3 from session 5, the second of four after lunch. None of these laps were under two minutes but they include some fun, passing slower cars.
The video includes quite a bit of on-screen data. The vertical histogram at the left shows throttle position; the target to its right shows two-dimensional acceleration. The two horizontal bars at bottom left show RPM and the turbocharger's boost pressure, with the numeric values to their right. At lower right is a map of the track showing the current track location in the video. (Video from the Track Addict app with additional data via a PLX KIWI 3 OBD adapter.)
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Copyright © 2020-2021 Karl L. Swartz. All rights reserved. |
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