The theory of High Performance In this thread Im going to post a few thoughts on the theory of optimizing performance - according to the numbers. Real world situations may yield different results. Changing gears: Maximum speed in each gear is: 1st 47mph 2nd 65 3rd 88 4th 111 So you can reach 60mph in 2nd gear, and 100 in 3rd, but will redlining each gear before changing up give you the fastest times? Actually, no because the gear spacing is different between the gears. If you travel at 30mph the rpms needed to maintain that speed is: 1st 5800rpm 2nd 4000 3rd 3000 4th 2250 The key to changing gears is to arrive in the NEW gear at maximum engine torque which prevents the car from bogging down when it is too far down in the power band. A careful look at the 458 torque curve shows that it is relatively flat at 310 ft-lbs from 4000 to 7000 rpms then it trails downward to 250 ft-lbs at 9000rpm. Horsepower is a factor too, but it is actually the integral under the curve which is important. When all is calculated and done, at 7000 rpm, the car is generating the greatest combination of torque and horsepower, so this is where you want to land when changing gears. Notice that the drop in rpm from 1st to second is almost 2000 rpm, so the change should occur at the 5th LED which comes on at 8920 rpm and will drop you to the magic 7000 rpm number. The drop in rpm from from 2nd to 3rd if you're going 0-60 and from 3rd to 4th if your going 0-100 is 1000 rpm, so you want to change at the 4th LED which comes on at 7750 rpm to drop you to the magic 7000 rpm number. If youre skillful enough to do this, what does it gain you over just changing at redline? In my personal and very amateur experience, about 0.15 seconds in 0-60 and about 0.3 seconds in 0-100. What if I don't change gears at all and just leave the car in manual? The 458 will upshift all by itself at each redline, and the times will be no different than changing yourself at redline. What if I put the car in Automatic? The car will upshift according to your recent driving habits. So if you cruise out and try it the first time the car will be sluggish, but if after some spirited driving the automatic will shift at redline, just as if it was in manual. So if you REALLY need that edge to get to 100mph; Foot to the floor, upshift at LED 5, LED4, LED4 and youll be there before your eyes stop watering!
This is incorrect. Simply put...in most cars (including the 458), torque multiplication from the gearbox is a bigger factor than the torque curve of the engine. So for maximum acceleration, shift each gear at the 9000 rpm redline. The mathematically correct way would be to plot thrust at the wheels (thrust = torque x gear ratio x final drive ratio x wheel circumference) vs speed in each gear, and shift gears to maximize thrust for any given speed. The math will show that shifting at redline in each gear yields the best acceleration.
If the engine has its peak torque at of 540NM at 6,000rpm, do we change gear at the moment the 3rd LED(7,000pms) lights up? Image Unavailable, Please Login
The general rules are just that --general rules. In theory you have to work out optimum shift points for each set of engine torque curves and gear ratios. The slide below is a conceptual example that illustrates the fact that the optimum shift point is the point at which the combination of the higher gear ratio and torque at the lower engine RPM exactly equals the combination of the lower gear ratio and torque at the higher engine RPM. In the example, the gear ratio change is 1.5:1 and the torque curves are simple parabolas. The diagram shows schematically (the small triangles) the penalty for shifting too early or too late. Image Unavailable, Please Login
Conceptually yes, an upshift at 7000 rpm would put the car at maximum torque the instant the car is in the new gear. However, as bus driver has said, it is a little more complicated than that since horsepower does factor in. Horsepower continues to climb throughout the rpm band, which is why landing in the new gear at 7000 rpm gives slightly better results. Ferrari is to be commended for engineering such a flat torque curve which means that on a track heading into a corner there is a large range of rpm from which you can downshift that will give you a similar torque rating in the new gear. This means that the way the car accelerates away from the apex will be largely predictable and reproducible
Stay in the torque range! Basically and presuming most cars have around 1,000 rpm or less drop from a lower gear to a higher gear, the important thing is to shift while in the power band the next higher gear without compromising torque. This varies from car to car. Best
Unfortunately this thread sounds like someone who is conducting these studies in speed on I city streets. Abruptly hammering on the throttle on cold tires can turn out badly!
Actually, maximum acceleration is usually achieved by shifting a little after the hp peak. HP factors in gearing, torque doesn't so is a virtually meaningless number without knowing the rpm it occurs at (which is actually horsepower).
Slippery when dry? I took my trusty accelerometer out to a deserted road on the edge of town for a few performance starts - or so I thought. First off: Worst case scenario for a baseline Wet mode Automatic Right foot on brake Then right foot full accelerator 0 - 60 in 4.1 seconds. Fair enough. Now for some fun: simulating a street start from a red light. Race mode Automatic VDA all systems GO Right foot on brake Then RIGHT foot full accelerator 0-60 in 4.0 seconds. Well thats very disappointing! Thats not going to beat out a Shelby :-( Getting serious now: Launch control performance start (Disclaimer for those of you who read ALL the threads: I am a Doctor, a Radiologist, who sometimes does Interventional Radiology, and yes, I work really hard seeing patients, but no, no one in my family is famous enough to be searched on the internet!) Race mode Manual transmission Autolearning successful VDA all systems GO LEFT foot on brake Press Launch - PS lights up in tach and warning beeps While LEFT foot is still on the brake, RIGHT foot on full accelerator Tach settles at 3000 rpm lift LEFT foot off brake and GO! Well, the tach bogged down to 800 rpm before the car moved started to move. 0-60 in 3.9 Thats not supposed to happen. :-( At first I thought I did something wrong, but later realized that even in Launch mode, the traction control is still ON, and the system will keep slowing down the rpm until the wheels obtain traction. So even though the road was dry, its composition was such that the traction was no better than in wet mode. That was quite a surprising revelation to me, but it does make sense that ultimately traction is the limiting factor. I have Pirrelli PZero tires. I was a little ticked off at this realization so I did a vengeance run Traction OFF manattino at setting 5 (red setting on VDA) Launch control start as above. The tires smoked, the back end fish tailed slowly but controllably all the way to 60 mph 0-60 in 4.7 seconds. Although not terribly scary compared to my Z06 Corvette, I put the car back into sport, and probably wont ever do that again, unless I want to drift on a track. As I drove home I recalled an article I read where Randy Probst from Car and Driver was slower around the track in a ZR1 with traction control off than when he had it on. I know just where to find a stickier road
Err, no. Maximum acceleration over any period (rather than instantaneous) of time takes place that has the most area under the HP curve. period. Modern high performance engines will always be shifted at redline in order to achieve this.
