5% Power Increase = ???

[chinnam3]

Tesla is advertising the 0 - 60 time of the Model 3 LR as 5.0 seconds. IIRC it was 5.3 seconds before the firmware upgrade.

Before firmware update 0-60 was 5.1 for LR, not 5.3.
So, as per new spec, it improves by 0.1 from 5.1 to 5.0

 

[SageBrush]

Before firmware update 0-60 was 5.1 for LR, not 5.3.
So, as per new spec, it improves by 0.1 from 5.1 to 5.0

IIRC you are quoting a time with a roll-out.

 

[alienranch]

I was pointing out the greater discrepancy between peak power and average power in your ICE cars to explain your experience. If you knew the average power increase in your beefier car you would find that the improvement in race times is ~ proportional.

The good news is there’s no way to loose getting more power for free! We all win.

 

[mongo]

That's already significantly cutting into SageBrush's time, which is exactly what I'm saying. If you're going to use physics calculations to determine an outcome, you can't pick and choose what variables you want to include. He's excluding numerous factors ranging from rolling resistance, wind resistance (which increases exponentially), traction, traction management and slippage, ability to supply the power (injectors, intake, etc for ICE, and discharge rates for EV), and a host of other factors honestly far in excess of my knowledge. It doesn't take a rocket scientist to understand this. a typical 500hp sports car hits 60 in the mid 3 second range. Does anyone really think a 900hp car does the same thing in .7 seconds? Power increase and acceleration are absolutely related, but not linear (1:1) in the real world.

Comparisons between ICE cars don't work because they have a torque curve/ Depending on shape, the power band of one is more advantageous that the other. Plus gearing and all that
For an EV with no drivetrain changes, a 5% increase in power means a 5% increase over the entire portion of the curve that is power limited (low end is current limited at the motor, high end might be voltage limited due to back EMF.

You do raise a valid point in terms of real world performance. The aero and rolling resistance sum to a force needed to maintain speed, this is subtracted from the total force available from the motor. The remainder then acts on the mass to accelerate it.
Due to this initial subtraction, the 5% power (or force) increase results in a greater that 5% increase in acceleration at any point in the profile.

Example:
Say you start with 20 units of force, and need 10 to counter aero and rolling, you have 10 units to accelerate with.
Now, say you have 5% more, or 21 units. Operating conditions are the same, so you knock off 10 unit leaving 11 units for acceleration, a 10% increase.
Again, at the high end and low end this doesn't work due to other limits, only where there was a power limit applied.

 

[Knightshade]

I haven't seen any date from Tesla on M3 AWD (non-P) and site still shows the same. Did I miss something?

P and LR RWD both got a 0.1 listed improvement. AWD did not.

My speculation is this is them wanting to make LR RWD look like a "better" deal worth upgrading to from MR now that it's available again... and they want to (for a second time) dishonestly make P look like a more worthwhile upgrade from AWD than it really is.


They did the same thing (with P) when they dishonestly began including rollout in its 0-60 (going from 3.5 to 3.3 without actually changing the car in any way) but did NOT do that for RWD or AWD.

IIRC you are quoting a time with a roll-out.

See above.

LR RWD and AWD (and all non-P S and X models as far as we know) are quoted without a 1 foot rollout allowed... (5.1 and 4.5 originally- now 5.0 and 4.5 in the recent 5% update posted numbers, even though nobody HAS the new firmware yet)... and all P models are listed with the rollout allowed to dishonestly make the Ps look quicker in comparison. (3.3 instead of 35 originally on the 3, now 3.2 with the 5% thing nobody really has yet)

They've been doing this for years.

They briefly stopped doing it, on the 3 only, when the P3 launched- but then switched back to the dishonest S/X method some time later.

 

[AlanSubie4Life]

Power * time = work
Since work is ~ constant, power and time are inversely proportional.

If power were constant, or even if it were NOT constant and went up proportionately over the entire time period of interest, what you're saying would be true. We currently don't KNOW what Tesla will be doing, but they have only mentioned the peak HP increase. They have not discussed increasing torque. It makes a big difference to what happens to 0-60 times. More below.

I'd recommend reading the threads mentioned above which have some data which make it easier to see what is going on.

My 460hp Corvette does 0-60 in something like 3.4 seconds. My 650 hp Viper does 0-60 in about 3.1 seconds, yet it has about 40% more power. By your calculations my Viper should be hitting 60 in the low 2 seconds which is ridiculous. Same goes for top speed. Corvette does something like 190 but my Viper tops out at 208. Shouldn't it top out at almost 270 by your linear calculations?

I think (aside from grip limitations and the time to change gears) the main reason this doesn't scale this way is because the car is not operating at peak HP all the time. Torque at the wheels is what determines acceleration, and of course HP is Torque * RPM. It would be optimal to stay right on the HP peak and continuously vary the drive ratio to match the wheel speed exactly (because exactly correct gearing down from the RPM @ peak HP would result in maximum torque), but physically that is difficult to do. The gearing results in not producing maximum power all the time.

That's a sort of difficult thing to wrap one's head around though, so let's move to the EV case, since we don't have to worry about gears:

If you look at the P3D velocity vs. time plots in the threads above, you can see clearly that acceleration is constant up to 45mph. Torque is exactly proportional to acceleration, so torque is also constant.

That means that 1) Torque is constant and 2) HP (torque * RPM) is ramping linearly from 0HP (at 0mph) to 450HP (at about 45mph), where the software-limited current limit of the battery (and possibly the motor though we know it can take 5% more now) is reached. At that point, since no more HP can be produced, but RPMs are still increasing, torque (and acceleration!) start to decrease (since HP = Torque * RPM, and HP is constant). BTW, relatively soon thereafter, the HP also starts to drop off, and torque even faster than inversely proportional to RPM, in short because the motor is not ideal (not really that relevant to 0-60 times) and would need gearing to get back to a lower RPM again.

So, again, we don't know what Tesla will actually do. There are two likely scenarios:

1) Increase the maximum current (V*I = P so that increases the Power limit) that can be drawn from the battery. That would only result in constant torque being maintained to a slightly higher speed (about 47-48mph, 5% higher than the current point), and producing 5% more peak HP.

2) Do 1) AND increase the peak torque the motor can produce. This would increase torque and acceleration and HP all the way from 0mph to 45mph, and then torque would start to drop, but still be higher than the current case. Also would result in a higher peak HP (at ~45mph, since there would be more torque at the same RPM).

Scenario 2 results in much higher gains in 0-60 time because it affects the entire velocity vs. time curve starting at 0mph. I personally think that for the P3D scenario 1) is most likely, because the advertised change in 0-60 time is not large (and there may be a motor limit to maximum torque which has already been reached, or at least they aren't comfortable relaxing it yet). However, I think there's no reason they COULDN'T do scenario 2 for the RWD and AWD vehicles, but again, they only promised a peak HP boost. But they may also end up boosting torque at 0mph which would be awesome for those owners.

I don't have a VBOX velocity vs. time plot for the RWD and AWD vehicles, but they probably would still benefit more from scenario 1 than a P3D - because it's possible the HP limit is reached sooner (lower speed). But I think it's a combo of lower torque (which can obviously be increased on the AWD to match the P3D if they wanted) and a difference in where the peak HP is reached if you're comparing to the P3D. Hard to know, I am speculating.

Anyway, my point is that the exact result depends on exactly what Tesla changes. It can probably be inferred from the modified 0-60 times for each vehicle (but you have to compare apples to apples - watch out for the 1-foot rollout fiasco which only applies to the P3D times). One of these days I need to create a Matlab model but haven't got around to it.

 

[DrSmile]

From what I've read they're going to allow the motor to rev higher. They're assuming that the peak horsepower is at the top RPM, so allowing the motor to rev higher would increase the peak HP. Since there are no gears I would anticipate absolutely no difference in performance except a higher top end speed.

 

[AlanSubie4Life]

From what I've read they're going to allow the motor to rev higher. They're assuming that the peak horsepower is at the top RPM, so allowing the motor to rev higher would increase the peak HP. Since there are no gears I would anticipate absolutely no difference in performance except a higher top end speed.

They are allowing the motor to rev higher to increase the maximum speed, according to Elon.

However, the peak HP occurs far before max RPM. Due to issues with high motor speeds, back EMF, etc., HP drops off significantly by max RPM.

So allowing the motor to run to higher RPM has no effect on peak HP.

Peak HP in the P3D occurs starting around 45mph. It starts to drop off relatively soon thereafter (I haven’t measured with a VBOX but the dyno plots give a rough idea).

 

[AlanSubie4Life]

Just to complete the picture on this max speed/peak HP increase compared to where we are:

For P3D:
Wheel circumference: (2*(235cm*0.35/25.4mm/in)+20in) * pi = 83.18in = 6.93 ft
Drive ratio: 9:1
Max speed: 162 mph = 14256ft/min
Wheel RPM = 2057rpm
Motor RPM @ 162mph = 18514rpm (Elon said "something like 19000rpm")

Incidentally, while on the topic, I drew a line on the velocity vs. time best fit for my P3D between 5mph and 35mph (where it is clearly perfectly linear, implying constant torque), just to see where it started deviating (what speed), because that deviation point shows where the HP limit is reached.

This shows deviation occurring at around 45mph.

Also, let's take the Tesla numbers (in the Road & Track article) which specify (before the power bump) 450HP and 471lb-ft of torque (I guess these are from Tesla? Presumably these are at the motor output, not to the wheels, so you can't use them directly for calculating acceleration, but that is not what we are doing here). If we assume perfectly linear increase in HP up to the limit (which doesn't seem unreasonable based on my plot, although the dyno plots are more confusing - I think because of measurement error & smoothing):

HP = Torque (ft-lbs) * RPM / 5252 => RPM @ initial Peak HP = 450 *5252/471 = 5018RPM.

What speed is this? Wheel RPM = 5018RPM/9 = 557.6RPM

Using ratios from info above:
557.6/2057 = x / 162mph => x = 43.9mph

So looks like max HP occurs at 44mph

Here's the plot from the P3D. You can see definite deviation around 45mph. So it all lines up pretty well.

Now imagine they just increase peak HP by 5% by "pushing out" the straight part of the line to 47 or 48mph. It'll have very little effect on 0-60 time (probably 0.1second). Now if they increased the slope (more torque!), THAT would help.

 

[apacheguy]

Has anyone actually measured (in terms of kW) the peak power difference for LR RWD?