I for one appreciate the explanation as I didn't fully understand it.
I still kind of hate it. Get off my lawn.
Photography Credit: Dave Green
Those watching any portion of the Rolex 24 on television didn’t hear a rather familiar word mentioned: fuel.
While some just dismissed this language as greenwashing the sport, there’s a perfectly reasonable explanation for the change in terminology that makes “energy” a far more appropriate descriptor.
That explanation starts with torque sensors, which were previously installed only on GTP cars but are now part of the standard across the IMSA WeatherTech SportsCar Championship classes. These load-based torque sensors, which, according to Stu Brumer of Turner Motorsport, cost around $60,000 to integrate into a GTD car, pick up the rotational force of a drive axle. Think of them as tiny, onboard dynos.
A torque sensor from a previous year's Acura GTP race car. Photography Credit: J.G. Pasterjak
These sensors are the key to how IMSA now regulates the ultimate range of the cars. Instead of listing a given fuel capacity in the rulebook, each car’s spec line now has its maximum stint energy expressed in megajoules. That’s the total amount of energy each car can expend, as measured by the torque sensor, before it has to visit the pits.
The specs also express a maximum energy replenishment rate in MJ/sec. for each car.
In the case of the GT3-based GTD field, as well as the LMP2 cars, all of that energy is currently being produced by combustion engines. But in the case of the hybrid GTP cars that also have an additional 240 horsepower of electric propulsion via a spec hybrid drive system, they take on not only liquid fuel but electrical energy during their stops.
And while those hybrid drives are spec units, their integration and software are up to the constructors to figure out for themselves. The trick here is that any energy recovered during a stint goes back into the energy bank–think of it as selling the rear seats out of your $2000 Challenge car every time you coast or hit the brakes. So a successful strategy for recovery of that kinetic energy can extend a stint, which could be very helpful in IMSA’s endurance format.
Note that all these calculations have been tuned to result in very similar action to what we’re used to. On-track stints are still in the 45-to-55-minute range depending on how aggressively the teams are pushing the cars, or how efficiently the teams are running an energy recovery strategy in the case of GTP, and IMSA still wants full replenishment of energy–what we used to call a full fuel fill–to come in around the 40-second mark.
And yes, GTD and LMP2 cars are still just using liquid dinosaurs. So speaking of “fuel” in those cases would still be appropriate.
But the way the regulations are written now, using “energy” is really a more apt descriptor, since that’s what’s actually being used as the metric by the stewards. They don’t really care how much gas you put in your BMW M4 GT3, for example, but you can only produce so much power over the course of an entire stint.
So don’t think of the use of the term “energy” as greenwashing by IMSA announcers, but rather as a more specialized and more accurate way to describe the refueling process that better reflects what IMSA is actually regulating during competition.
I for one appreciate the explanation as I didn't fully understand it.
I still kind of hate it. Get off my lawn.
But the pictographs of "energy remaining" on the TV coverage were batteries. I'd have to go back and look, but I'm pretty sure they used that for every class.
That is sorta green washing, in my opinion. They're making it seem like electric power is involved where it isn't. And even in classes where electric power is involved, it's the minority contributor to the equation, so wouldn't have been my primary choice for how they'd show "energy remaining".
But I've been accused of being too literal before.
*Also, if they gave any detailed explanation of why they were using that nomenclature, I missed it, so I appreciate it being laid out here. Does at least make some sense now. Not all the sense, but some.
You lost me at requiring a $60k additional cost to a race car to basically monitor fuel efficiency.
Seems to me JG has been greenwashed himself, in trying to explain why this isn't greenwashing. 
I hate the whole thing.
What next? A "grip factor" for tires?
"Oh look, he's operating at only 10% of max grip -- better change those tires soon"
It seems like we're (once again) complaining about BoP here. This seems like a really elegant solution to BoP, and way way way easier than a million permutations of weight/fuel capacity/fuel flow/etc etc etc based on different powerplants across different tracks.
As silly as BoP is, it made for some VERY close racing this year.
Tom Suddard said:It seems like we're (once again) complaining about BoP here. This seems like a really elegant solution to BoP, and way way way easier than a million permutations of weight/fuel capacity/fuel flow/etc etc etc based on different powerplants across different tracks.
As silly as BoP is, it made for some VERY close racing this year.
I'm fine with the BoP usage. That's behind the scenes.
I'm not fine with the "energy" PR/Marketing speak from the talking heads.
And why are you back on my lawn again? I thought I told you already. 
As with any 'new' tech there can be problems. One of the Lexus RCF's had a data indication that it was at the end of its allowable energy range and was required to come to the pits despite only having used half of the 'energy' from the previous stop. The torque sensor'd drive axles also have potential issues and failure modes. All that is to say, when piling new tech on already complicated cars there are bound to be hiccups that may have effects to the larger participation of the manufacturers. These are not always considered by the sanctioning body.
The torques sensor'd axles have an interesting side effect to the BOP. From the table of the allowable weights, RPM's, wing angles, energy usage, and energy usage rate. there is set of power available versus vehicle speed. This effectively limits torque/power curves with some loose connection to aero configuration. There is also a footnote limiting power at low speeds, which would negate powertrains with very strong low end torque curves.
Based on the data in the table one could use the power usage rate (MJ/s), car weight and speed power allowances to create comparable acceleration curves for each vehicle, but you would have to ASSUME some drag numbers.
Energy limitations can also allow for different liquid fuel types to run in competition. The LeMans 24Hr race requires competitors to use the fuel they provide. The diesel cars all used the same fuel, the gas cars all used the same fuel. However the energy density of gas and diesel are not the same. Just for a quick recollection, the diesel fuel would evaporate off the ground faster than the gas, when spilled. That is not something I have EVER experienced at the local pumps. The energy density of the diesel may not have been the same as the fuel in the road cars in the paddock. This energy equivalency COULD allow custom fuels to be mixed by teams like it was in the F1 and 80-90's GTP days. We had to remap a Gurney Eagle GTP engine for modern fuel for Goodwood because the guy that mixed the fuel was no longer alive and the recipe was not documented...
Andy Hollis said:Seems to me JG has been greenwashed himself, in trying to explain why this isn't greenwashing.
I hate the whole thing.What next? A "grip factor" for tires?
"Oh look, he's operating at only 10% of max grip -- better change those tires soon"
Just be glad I wash myself at all
Someone needs to remind me the year they have fuel remaining as data.....
Complain all you want about it called energy remaining, this is data that was not available to viewers before. Now you can see how teams are balancing the performance with fuel usage. Something we all knew they did, but now you get to see it as a strategy live.
Does it really matter it's called energy?
(WRT combustion engines, putting it like that also forces the engine designers and developers to really push for maximum efficiency, too)
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