Stage 6: COVID
End track hours: ~140
End Laguna Seca time: <didn't go>
End parts/specs:
~3570 lbs max weight (150 driver, full tank); roughly 200 lbs reduction
SPL rear suspension links
Tires: RE71-r 275/35/18 square
Tires: Nankang AR-1 275/35/18 square
12 mm spacer front
MCS 2-way canister shocks
springs: 650 lb in F, 800 lb in R; 6 in tall; 2.25 ID
H&R 20mm rear sway bar
weld-in TCD rollbar
-3.8 F -2.5 R camber; 1/16 F -3/16 R toe
The M240 didn't see that much driving since the last "Stage", for several reasons. First, of course, COVID happened and the tracks were closed for a few months. Then, the first weekend they opened, the rear suspension suspended itself, so another several months in repairs and "while I'm there" upgrades. In the meantime, I finished building my
proper racecar, and the bulk of my time and energy went to "race it, break it, fix it". The M240 just sat quietly in a corner, ready to sub in last-minute when the other car had inevitable trouble. Horrible, horrible, first-world problems, I know.
As I wrote
earlier, switching to 275/35 tires and replacing the rear end bushings solved two of the biggest issues with the car so far -- failing sidewalls and wandering alignment. Two big ones remained.
First, the KW V3 shocks I had on were slowly starting to go. I first started noticing it near the end of 2019 -- with each track day, the car was getting more and more underdamped. It was especially obvious on tracks like Buttonwillow, where you really have to ride the kerbs to get a decent time -- after a kerb, the car would take 2-3 oscillations to settle. This led to at least one fun 100+ mph "
excursion". Ironically, the shocks survived all the kerb hopping of my first post-lockdown track day and let go on the highway a day later. Lots of shock oil sprayed all over RR. Also, with no dampening, the rear swaybar hit the suspension links and snapped, and the pieces managed to puncture the CV joint boots. Talk about an oily greasy mess.
I could've sent the KWs for a rebuild, but at this point they'd served their street/track purpose. Plus, I'd just gotten a tow rig for the MR2, so why not make the M240 less practical and barely streetable as well? So, it got proper motorsports shocks (MCS 2-way), another bump in spring rates (by about 25%), slightly lower ride height, and a 20 mm replacement rear sway bar (up from 19). Oh and a replacement axle because BMW doesn't sell a CV boot kit.
The second big problem, still unsolved, seems to be around overheating. In the past, I've ran it at 100+ ambient temperatures with no trouble at all. But since roughly the end of 2019 again, the ECU occasionally decides to partially cut the throttle on the straights. It took me a while to spot it in the data and convince myself I'm not just driving slowly ("low on power" is the oldest excuse in the book). But the data doesn't lie -- the throttle position occasionally goes down to ~70% while the pedal position is firmly at 100%. Needs more debugging and a cooling system refresh / overhaul.
Anyway, the suspension overhaul had at least some rationale (old one broke). The other updates were a little less... necessary. During the early lockdown months, I was getting pretty bored at home, so I started pulling the interior out to shed some weight. Got rid of the rear side panels, rear bulkhead, a/b/c pillar covers, stock belts, the headliner, and curtain airbags.
Next up was the sunroof. I just
wanted to take out the cassette and plug the hole with fiberglass / CF, like people have done on BMWs for decades, for not much money. Turns out, no one makes a delete panel for the F-chassis cars, and the shops that make the various e36/e46/e92 panels all politely told me to pound sand. I asked a local composites shop what it would take to make a one-off piece, they gave me a quote, and I ran away screaming. It was way cheaper to just get a full CF roof, so I just did that. Long story short, the car now weighs ~3570 lbs with a full tank and 150-lb driver, which would be close to 3300 empty. This round of weight reduction cut ~200 lbs from the interior, sunroof, and fender chassis bracing (to make room for taller tires). There's at least another 200 "easy" pounds left in carpet, battery, AC, door cards, etc.
But wait, there's more! With all the interior and sunroof stuff out of the way, the rollbar was now miles away from both the sides and the roof. Which is not an issue per se, but a lost opportunity for extra protection and chassis stiffness. Plus, it doesn't reflect greatly on the fabricator reputation. So, we replaced it with a shiny new one that's
nice and snug, plus welded in. This way, when the car inevitably goes wheel-to-wheel racing, it will only need a front half, and a few other small safety bits.
All these Very Necessary upgrades out of the way (and 6 months later), it was time to do some driving. To state the obvious, the car is noticeably faster -- even with the cooling issue cutting some straight line speed and masking some potential pace. I didn't go to Laguna Seca, which I use as a benchmark here, but on the other tracks, it dropped 2-3 seconds per lap.
The MCS shocks soak up bumps and kerbs like magic. It's very confidence inspiring. The rest of the setup changes (springs, bigger rear bar) also feel like a solid step in the right direction -- the car is definitely happier rotating now, without being snappy. If anything, it can probably go a little looser without much trouble.
Front camber right now sits at -3.8, which is too much for the current set of springs / tires. The insides tend to get chewed up under braking pretty fast. Will revert back to -3.5, which is gentler on them.
Speaking of tires, I tried some Nankang AR-1s in addition to the RE71r-s I've grown used to. I've only gone through a single set, so impressions are still initial, but very positive. They're definitely grippier than the 71rs and surprisingly similarly durable (though need to get through a few more sets to judge that). They're at their best at lower pressures -- 32 psi and under for our cars -- and need a bit more warmup.
That's it for now. No more major upgrades planned in the near future, just some small setup tweaks and more hours on the current parts. And sorting out the cooling issue to get back to full power.
