ACR Extreme vs. Porsche 918 Laguna Seca Record Run

[PAVenomRT/10]

I thought it would be interesting to compare the 2 videos of the Randy Pobst Laguna Seca record runs in the 2 cars. I wanted to see how the Viper beat a car with 300 more hp and all wheel steering and 4 wheel drive. The minimum speed of the Viper exceeded the minimum speed of the 918 in each corner by about 5 up to 13 mph. The faster the corner, the greater the differential as one would expect based on the greater aero downforce in the Viper. The Porsche exceeded the maximum straightaway speed of the Viper by a similar amount. For example, coming off the last turn approaching the finish line the Porsche hit 132 while the Viper hit 119. Despite the greater acceleration in the Porsche, the Viper was over a second faster in its record-setting lap (128.69 vs. 129.89). This underscores that on a track like Laguna Seca, corner speed is more important than acceleration due to the total amount of time spent cornering vs the straightaways. Very impressive performance by the ACR Extreme.
PAVenom RT/10

[TrackAire]

I would like to know the straight line speed of the 918 after 3 or 4 hard laps....would it slow down due to the battery being out of juice and now is just dead weight?

I would not be surprised if the 918 lost 2 to 3 seconds a lap after the juice runs out.....but nobody will ever test that, lol.

[PAVenomRT/10]

Don't forget that these hybrid cars utilize regenerative braking to recharge the battery so running out of juice should not be an issue.
PAVenomRT/10

[dethred]

They won't regen 100% of the time, and it'll eventually run flat, or charge partially and then discharge quickly again. Physics.

[ViperPete]

I thought that those hybrid sports cars only have like 10-15 miles of electric time.

So on a 100 lap race it defiantly would be dead weight.

[dethred]

I thought that those hybrid sports cars only have like 10-15 miles of electric time.

So on a 100 lap race it defiantly would be dead weight.

All of them regenerate the batteries to some extent, but the car is leaving the paddock with more energy in the batteries and fuel tank than it will ever manage again at race speeds.

Think of them like the new Z06; a few minutes all out, several minutes recovering.

[ViperPete]

All of them regenerate the batteries to some extent, but the car is leaving the paddock with more energy in the batteries and fuel tank than it will ever manage again at race speeds.

Think of them like the new Z06; a few minutes all out, several minutes recovering.

That's what I think too.

We sell the Leaf here at Nissan. It has about an 80 mile range. That includes stopping and slowing down.

I cant see how 1-2 seconds of braking and WOT all the time can possible be handled by a hybrid sports car.

[serpent]

That's what I think too.

We sell the Leaf here at Nissan. It has about an 80 mile range. That includes stopping and slowing down.

I cant see how 1-2 seconds of braking and WOT all the time can possible be handled by a hybrid sports car.

With better technology. F1 uses regenerative braking (KERS) when the car is under braking the energy is stored back into the batteries. I think only the 918 uses that technology on current production cars.

[Jack B]

You are correct, they are not perpetual motion machines and the losses are fairly high.

They won't regen 100% of the time, and it'll eventually run flat, or charge partially and then discharge quickly again. Physics.

[Car457]

So I have a friend with one of these 918s. To shed some light on the battery charge/discharge cycle, one will run a full battery down to about 25% after 6 hot laps at Road America (24 miles). If you then back off on hammering the throttle for 2 laps the battery will have charged back up to about 90%. The liquid cooled battery pack accomodates the super aggressive charge/discharge cycles. The track optimized 919 winning 2015 record is signaling that there may be something to this architecture. By the way, my friend has orderded an extreme ACR!

[LABrit]

So I have a friend with one of these 918s. To shed some light on the battery charge/discharge cycle, one will run a full battery down to about 25% after 6 hot laps at Road America (24 miles). If you then back off on hammering the throttle for 2 laps the battery will have charged back up to about 90%. The liquid cooled battery pack accomodates the super aggressive charge/discharge cycles. The track optimized 919 winning 2015 record is signaling that there may be something to this architecture. By the way, my friend has orderded an extreme ACR!

Ths is correct.

You guys are way off with your assumptions of physics - the faster the 918 goes in track mode the quicker the regen.

[Snakebit10]

This is Porsche we are talking about not GM so I will bet they engineered in ways of dealing with all of the heat and regen issues etc while allowing the car to operate at peak or very near peak over the lapping sessions.

[DLA]

Who cares what the Porsche batteries are doing! After lap one it's a second behind the Viper. After lap two it's two seconds behind and so on. The Porsche will not catch up and will fall further behind as it fights its own weight and heat soaked engine.

[345s-bspinnin]

No need to speculate or infer from two videos spliced together. Motor Trend super imposed telemetry data for the ACR record run against the 918 and P1 at Laguna Seca. There is plenty of data to be assessed and analysed for the ultimate bench racer.

Link to MT site, Wrecking the Production Car Lap Record at Mazda Raceway Laguna Seca


A few key charts below. (Images are huge and too large to auto-size or reference locally, zoom out or click on the link)





They also included their TA Record Run against the ACRs:

[dethred]

Ths is correct.

You guys are way off with your assumptions of physics - the faster the 918 goes in track mode the quicker the regen.

Physics are against it ultimately. The only benefits of the electric motors are when it's fully charged before starting a session, and it recovers some of the braking losses. The engine will only be efficient in charging the batteries on decel, otherwise it's drawing power from the gasoline engine. It is not going to regenerate at 100% efficiency, so it's trading weight for more power in short bursts. The gasoline engine is not going to charge the batteries on acceleration, or if it does it will be reducing the power going to the wheels.

As the car accelerates down the track it is expending energy from both motors. Aerodynamic drag, tire rolling resistance, and the impossibility of 100% efficient recharging means the energy spent on acceleration will never be fully recovered under deceleration.

Don't believe me? Ask yourself why the batteries drain in the first place. Think of it like those toy bouncy balls: You drop it, but it can never bounce up to the height from which you dropped it. I'm not saying it makes the cars slower, but it's taking a different approach to making more power, and will never maintain the same speeds after the initial charge has been used.

[TrackAire]

Physics are against it ultimately. The only benefits of the electric motors are when it's fully charged before starting a session, and it recovers some of the braking losses. The engine will only be efficient in charging the batteries on decel, otherwise it's drawing power from the gasoline engine. It is not going to regenerate at 100% efficiency, so it's trading weight for more power in short bursts. The gasoline engine is not going to charge the batteries on acceleration, or if it does it will be reducing the power going to the wheels.

As the car accelerates down the track it is expending energy from both motors. Aerodynamic drag, tire rolling resistance, and the impossibility of 100% efficient recharging means the energy spent on acceleration will never be fully recovered under deceleration.

Don't believe me? Ask yourself why the batteries drain in the first place. Think of it like those toy bouncy balls: You drop it, but it can never bounce up to the height from which you dropped it. I'm not saying it makes the cars slower, but it's taking a different approach to making more power, and will never maintain the same speeds after the initial charge has been used.

Apparently somebody was awake during high school physics class!! Your answer is spot on in my opinion.

What I would like to know is this....has anybody ever run the 918 for at least 20 minutes on track in the hands of a pro quality driver? I'm thinking that you would see some serious heat issues or system "reduced power" warnings so the car and batteries can self preserve themselves.

[LABrit]

Physics are against it ultimately. The only benefits of the electric motors are when it's fully charged before starting a session, and it recovers some of the braking losses. The engine will only be efficient in charging the batteries on decel, otherwise it's drawing power from the gasoline engine. It is not going to regenerate at 100% efficiency, so it's trading weight for more power in short bursts. The gasoline engine is not going to charge the batteries on acceleration, or if it does it will be reducing the power going to the wheels.

As the car accelerates down the track it is expending energy from both motors. Aerodynamic drag, tire rolling resistance, and the impossibility of 100% efficient recharging means the energy spent on acceleration will never be fully recovered under deceleration.

Don't believe me? Ask yourself why the batteries drain in the first place. Think of it like those toy bouncy balls: You drop it, but it can never bounce up to the height from which you dropped it. I'm not saying it makes the cars slower, but it's taking a different approach to making more power, and will never maintain the same speeds after the initial charge has been used.

It doesn't need 100% efficiency to accomplish what it sets out to achieve. Of course 100% would be perfect but what is? I've had seat time in the 918 and know first hand how it regenerates under varying loads and can advise you that it can sustain heavy track use and each time it comes in from a session it will have just as much if not more charge than it went out of the pits with.

[ViperSmith]

I think the gripe people have isn't that the 918 isn't a great car, is that it is a "hero lap" car. Nothing wrong with that, but it won't run all day like the Viper at WOT.

Give me one, I'll glady take it

[Jack B]

You have just proved that super conductors and perpetual motion are possible

Keep mind the battery monitor was installed by VW.

It doesn't need 100% efficiency to accomplish what it sets out to achieve. Of course 100% would be perfect but what is? I've had seat time in the 918 and know first hand how it regenerates under varying loads and can advise you that it can sustain heavy track use and each time it comes in from a session it will have just as much if not more charge than it went out of the pits with.

[socal]

You have just proved that super conductors and perpetual motion are possible

Keep mind the battery monitor was installed by VW.

While I was earlier going to incorrectly point out that this would only be true if the car and brakes never got hot (leaking power, so to speak), it is very possible that the car returns to pit with more electricity given the fact that it has less gas in the tank. Perpetual-motion witchcraft would only be necessitated if it didn't burn some gas too ;-) Example: Turn three can only tolerate 40% engine output to the wheels before spin-out, so through German sorcery the vehicle runs the engine at 50% and diverts 10% output to charge the battery faster than just braking alone could accomplish. The batteries charge far more than just while braking. There's a reason we almost became a German speaking country.

[dethred]

While I was earlier going to incorrectly point out that this would only be true if the car and brakes never got hot (leaking power, so to speak), it is very possible that the car returns to pit with more electricity given the fact that it has less gas in the tank. Perpetual-motion witchcraft would only be necessitated if it didn't burn some gas too ;-) Example: Turn three can only tolerate 40% engine output to the wheels before spin-out, so through German sorcery the vehicle runs the engine at 50% and diverts 10% output to charge the battery faster than just braking alone could accomplish. The batteries charge far more than just while braking. There's a reason we almost became a German speaking country.

Color me skeptical.

“You have to get the lap time done while the batteries are up." - Randy Pobst

There is even a hot lap mode in which the 918's times were recorded, but that isn't what you were experiencing. I have no doubt that it can keep the battery charged, just not while coming anywhere near the performance of it running flat out on a full charge. There is no way in hell that car will leave the pits on a full charge, run flat out for a session, maintain consistent lap times at full performance, and then come back in with a full charge. It's just not possible in the physics of this universe.

[socal]

Color me skeptical.

“You have to get the lap time done while the batteries are up." - Randy Pobst

There is even a hot lap mode in which the 918's times were recorded, but that isn't what you were experiencing. I have no doubt that it can keep the battery charged, just not while coming anywhere near the performance of it running flat out on a full charge. There is no way in hell that car will leave the pits on a full charge, run flat out for a session, maintain consistent lap times at full performance, and then come back in with a full charge. It's just not possible in the physics of this universe.

I'm the first to admit that I have no idea what I'm talking about regarding what the 918 is actually engineered to do; however, what I am saying is that it is very possible "in the physics of this universe" to accomplish this because of one detail. The car may be running "flat out" for an entire lap, but the engine is absolutely not. And during the times when the engine has the ability to generate unused kinetic energy (which is in nearly every turn), the batteries can be charged at a rate far greater than that of regenerative breaking. That being said, I too am skeptical that they incorporated this level of tech into the rig. But you never know with sie Germans...

[TrackAire]

I think the batteries, motors and associated hybrid parts add approximately 700 lbs to the 918's weight. Can you imagine how fast the 918 would be if the gasoline motor put out around 725 hp with a curb weight of 2900 lbs by deleting all the hybrid parts? I absolutely love the look of the 918 but in my opinion, supercars shouldn't weigh more than a new Mustang V8. A lower curb weight would definitely help increase lateral G's and shorten up braking distances.....maybe enough to threaten the ACR's lap time at Laguna Seca.

[Photog1]

So I have a friend with one of these 918s. To shed some light on the battery charge/discharge cycle, one will run a full battery down to about 25% after 6 hot laps at Road America (24 miles). If you then back off on hammering the throttle for 2 laps the battery will have charged back up to about 90%. The liquid cooled battery pack accomodates the super aggressive charge/discharge cycles. The track optimized 919 winning 2015 record is signaling that there may be something to this architecture. By the way, my friend has orderded an extreme ACR!

A friend .. I think I know your friend he is pretty close to you right?

[Car457]

Another interesting point from my friend with the 918 is that you really don't want to roll out on the track with a fully charged battery. The electric motors can only be used in regen braking mode if the battery can accept a charge. Regen braking has an advantage in saving brake pads and hauls this heavier car down quite well. The ccb pads run in the 400 deg range when off the track for 5 min. Haul down example: Last turn braking at Gingerman can still start at same marker as in viper but speed is 150's instead of 120's of viper. Hybrids do need to lose weight generally. Rumors of a new battery technology swap out down the road are intriguing especially if lighter (eg 20%). I'm a fan of both cars and what a present the extreme ACR is to us from Dodge. Merry Christmas VOA!