Model S on the Track - A Review

[Doug_G]

You can't tell with Model S because they don't give you temperature readouts.

I've done several track days with the Roadster, and it does have temperature readouts. For Roadster motor cooling is clearly the major issue. Inverter temperatures could also cause a limit, but I've always hit the motor limit first at the track.

It takes a fair bit of flogging to heat up the Roadster battery, as it has strong cooling and a lot of thermal inertia. I've never had an issue with the battery causing a power limit; it's never exceeded ~ 40C. The air conditioner kicks in and holds it there.

I suspect the Model S is similar. Prime suspect motor, second suspect power inverter, battery could be but probably is not the cause.

 

[mnx]

"btw on the track (as I'm sure you know) we are power limited after about 10 minutes (4-5 laps usually) anyhow so its all about the HANDLING so lines can be precisely driven and what ever available power applied to the road in the most efficient manner. To me that means suspension upgrade is more important the the extra horsepower of the Perf."

So there you have it, the standard 85 can go much longer than the p85 without limiting power. I reached the power limit on my p85 after 1 lap or 1.5 minutes... I wonder how the power limited p85 compares to the s85 on the track.

 

[Doug_G]

So there you have it, the standard 85 can go much longer than the p85 without limiting power. I reached the power limit on my p85 after 1 lap or 1.5 minutes... I wonder how the power limited p85 compares to the s85 on the track.

I guess that makes sense - if you can't pump out as much power, it's not going to get as hot as quickly. Hmm... P85 drivers shouldn't hold the pedal to the floor?

 

[mnx]

I guess that makes sense - if you can't pump out as much power, it's not going to get as hot as quickly. Hmm... P85 drivers shouldn't hold the pedal to the floor?

Is your license plate covering the air intake at all? (I looked at the pics on page 1, and it does seem to be at least partially covering the grill) I have mine mounted down there, I assume I would get some benefit by removing it, just not sure how much.

 

[Doug_G]

Is your license plate covering the air intake at all? (I looked at the pics on page 1, and it does seem to be at least partially covering the grill) I have mine mounted down there, I assume I would get some benefit by removing it, just not sure how much.

Yeah, it is in front of some of the air intake, but I don't think that's relevant. It's more open than it looks, and with the pressure on the front of the car there will be plenty of airflow around behind the plate. Once you get a certain amount of air flow through a heat exchanger, additional air flow doesn't do much. Also my experience is basically the same as being reported by other owners who have tracked their cars.

If I had to guess, the weakest link is probably still the motor. I imagine it's pretty hard to transfer heat rapidly from the inner spool of the motor. The only mechanical connection to the rest of the car is through the drive shaft (there's no electrical connection except through magnetic fields). Resistive looses in the inner spool will doubtless heat it up pretty quickly under consistent high load.

 

[mnx]

I guess I'll just leave my license plate where it is then...

I tried sending an e-mail to JB last week to see if he could verify that the motor is the weak link. It sure would be nice if they could engineer it so that it didn't have to limit power.

I think I may try taking it easy on the straights tonight, that should cause the motor or whatever to heat up less, giving me full power for longer on the curvy parts of the track. Hopefully it will also get me a few extra laps. My father in law lives 13km from the track and he installed a 14-30 for me last night. That way I can at least begin the session with a nearly full charge.

Yeah, it is in front of some of the air intake, but I don't think that's relevant. It's more open than it looks, and with the pressure on the front of the car there will be plenty of airflow around behind the plate. Once you get a certain amount of air flow through a heat exchanger, additional air flow doesn't do much. Also my experience is basically the same as being reported by other owners who have tracked their cars.

If I had to guess, the weakest link is probably still the motor. I imagine it's pretty hard to transfer heat rapidly from the inner spool of the motor. The only mechanical connection to the rest of the car is through the drive shaft (there's no electrical connection except through magnetic fields). Resistive looses in the inner spool will doubtless heat it up pretty quickly under consistent high load.

 

[jat]

So I take it you monitored your projected range and it never fell below 30 miles or so? At 1200Wh/mi, you only have 71 miles of projected range with a full charge, so at about 42% SOC you would fall under that number with that consumption.

When I was at the track, I started the last session with 60 rated miles. I wasn't looking at projected range, but it didn't start limiting power until just before I pulled off the track with 17 rated miles left, so I am sure projected miles were way under 30. I really think it only limits based on drivetrain temperature and overall battery SoC (when the SoC is lower, you want to limit the discharge rate of the battery as well).

 

[mnx]

I wonder if adding a pre-cool motor/battery etc. function in the firmware would help at all. It's such a tease going out for only 3 laps at a time. I don't want to be out on the track putting along giving Tesla a bad name.

I had a guy walk up to me last night blown away by how fast the car was, remarking how it kept up with a GT-R down the front straight he asked how much torque it had etc. This is the impression I want leave people with.

 

[Cutwolf]

Tangential but...if the power limit happens due to overheating, is there any real risk of this happening in heat waves, or is it something unique to goingall out on a track?

i have no idea, just genuinely curious.

 

[mnx]

Tangential but...if the power limit happens due to overheating, is there any real risk of this happening in heat waves, or is it something unique to goingall out on a track?

i have no idea, just genuinely curious.

Power consumption is about 5X on the track vs. normal driving thus generating much more heat than normal. IMO there is zero chance of that happening during a heat wave. (Although I live in Canada, best to ask somebody from AZ

 

[Doug_G]

Power consumption is about 5X on the track vs. normal driving thus generating much more heat than normal. IMO there is zero chance of that happening during a heat wave. (Although I live in Canada, best to ask somebody from AZ

I'd totally agree with that assessment.

 

[vfx]

So 5 times the cooling needs to be added.

 

[Doug_G]

So 5 times the cooling needs to be added.

Or more. The drive train is probably not as efficient at full power.

The real question is: where is the thermal bottleneck?

 

[mnx]

I wonder if adding a pre-cool motor/battery etc. function in the firmware would help at all. It's such a tease going out for only 3 laps at a time. I don't want to be out on the track putting along giving Tesla a bad name.

I went ahead and e-mailed ownership with the suggestion. If I don't get a satisfactory response, I'll try contacting one of their powertrain and battery cooling systems engineers I found on LinkedIN...

 

[Denarius]

I'd be really curious to see dyno numbers before and after the limiting. I remember seeing one report of the car hitting 800+ ft pounds of torq (before the dyno operator had him stop).

 

[mnx]

I'd be really curious to see dyno numbers before and after the limiting. I remember seeing one report of the car hitting 800+ ft pounds of torq (before the dyno operator had him stop).

My butt-dyno tells me it's down on power a lot. It loses its ability to power-oversteer which makes it less fun.

 

[Denarius]

My butt-dyno tells me it's down on power a lot. It loses its ability to power-oversteer which makes it less fun.

Oh I don't doubt that one bit. My real question is if tesla's published numbers are a worst case (power limited) and not an optimal case (full battery no power limit).

 

[JRP3]

Anyone want to try using a compressed gas and a nozzle pointing at the radiator to supercool it? A NOS setup would be easy, though I don't know if there might be better gases to use for cooling. Pack some dry ice in front of it?

 

[mnx]

Anyone want to try using a compressed gas and a nozzle pointing at the radiator to supercool it? A NOS setup would be easy, though I don't know if there might be better gases to use for cooling. Pack some dry ice in front of it?

Now we're talking! Dump a bunch of dry ice in the coolant reservoir? LOL

 

[JRP3]

Here we go, this is what I'm thinking of http://www.enginebasics.com/Advanced%20Engine%20Tuning/Cryocooling.html


http://www.designengineering.com/catalog/cryo2-system-components