Damian completed four acceleration runs and one power curve run. The first run proved to be the fastest, a 15.2 second quarter mile at 95mph. Each successive run was between 15.25 and 15.4 seconds at about 93mph. The main problem that Damian had launching the 330 was that since the 330 has an open (non-limited slip) differential, the right-rear wheel would spin more and slow the run down. Even worse, if he got too excitable and gunned it too hard the dreaded "independent rear suspension wheel hop" reared its ugly head.
For those who aren't familiar with it, in place of the older-style solid rear axle where the two rear wheels are directly connected to each other, most newer cars use independent rear suspensions to give better handling since each wheel can follow the road's surface better. Unfortunately, what that also means is that unless the suspension is very heavily damped, if you hook up too hard the wheel bounds upwards and then rebounds downwards, giving the wheel a hopping motion of surprising energy. The best way to avoid it is to be smoother on the power, or just put less down. Putting down even more just leads to smoother -- but slower -- wheelspin.
Anyway, Damian decided that if you're going to do something, you should do it right -- so he staged a bit of a wheel hop clinic. You can see that for every run we experienced some wheel hop, but the third run was truly in a class of its own! That particular effort left a swerving, staccato-style set of tire tracks behind -- nice job!
In order to better see what went on during the launches you have to compare the launch RPMs. Unfortunately, the BMW's cigarette lighter proved to be too well electrically filtered and the RPM sensing of the G-Tech got rather confused. In order to make sense of things, I've split the RPMs into separate graphs for each run, and then laid a smoothed line on top to cover the dropouts: acceleration run #1, run #2, run #3, and run #4. The 330's engine is rated for peak power at 5900rpm, but its torque peak is fairly low at 3500rpm. During each run Damian launched somewhere between 2500rpm and 3000rpm, which was simply too much power for the suspension. The most violent wheel hop occurred on the third run, which also had the highest and most sustained RPM levels. By launching between 2000rpm and 2500rpm the least wheel hop and wheelspin should occur and a nice, hard launch will be the result.
Since the 330 and my G35 are very close in weight, performance, etc. I've compared Damian's best launch with one of mine. When you look at the launch times you can see that his 60' time is a couple tenths slower (which is significant within 60'), showing his launch wasn't very clean. When comparing the two car's RPM levels at launch you can see Damian used more RPMs than I did, in spite of the G35 having a higher torque peak and a limited slip differential. Geez, Damian, slow down! <very big grin>
The 330's rated power is 225bhp @ 5900rpm, and 214lb-ft of torque at 3500rpm. Due to the RPM sensing on the G-Tech not working 100%, we couldn't verify the torque curve given the software's limitations. I may be able to drag the information out of the raw data later... we'll see. However, from the acceleration runs' power curves, the measured output was 170-175bhp @ 5900rpm. Based off of a calculated aero drag of 14bhp and an 18% driveline loss estimate, that calculates to 223bhp @ 5900rpm. Boy, it just doesn't get any closer than that!
As we discussed above, the main problem was launching with too many RPMs and too much power for the suspension. Dropping the RPMs even by 500 should net a half-second 0-60mph gain and a tenth or two in the quarter mile. Nuff said!
The second thing to check is gear change RPMs. From the RPM graphs you can see that the 1st-2nd shift drops 2200rpm, the 2nd-3rd shift drops 2000rpm, and the 3rd-4th shift drops about 1600rpm. Given the peak power at 5900rpm and the torque peak at 3500rpm, that means that each shift should essentially be right at 5900rpm since even the 1st-2nd shift would only drop the RPMs to about 3700rpm. Easy to say, but in practice Damian found that the Bimmer revved so easily it was hard to shift "short" like that, and nearly every shift was at about 6200rpm (the RPMs peaked to 6400rpm, but Damian lifted the throttle at about 6200rpm.) During that time period the peak power fell from 175bhp to about 158bhp, which means that even a couple hundred RPM will make a difference. Keeping each shift at 5900-6000rpm will likely net at least one or two tenths in the quarter mile, with a couple mph higher trap speed.
As I mentioned before, due to Damian's gearing up for the weekend his ETs and trap speed was artificially poorer. Between my weight, the half-tank of fuel, and the stuff in the trunk there was almost 300 extra pounds on board.
Adjustments made to the run data include:
- Using Damian's first run as a benchmark, his recalculated quarter mile drops from 15.2 seconds @ 95 mph to 14.7 seconds @ 98 mph. Cool! And by cool, I mean totally sweet.
- Given a smoother launch and shorter shifts, the quarter mile ET should drop to the low-mid 14s. A 0-60 time in the low to mid six second range should also be reachable.