The details about the GTP hybrid engines

J.A.
By J.A. Ackley
Jan 29, 2023 | Acura, BMW, Cadillac, Porsche, IMSA, IMSA GTP, Acura ARX-06, Porsche 963

Photo courtesy Porsche

The big story heading into the 2023 Rolex 24 is arguably the new IMSA GTP class featuring hybrid engines. While all manufacturers use the same 50-kilowatt (67-horsepower) Bosch electric motor and Williams Advanced Engineering battery pack, the ICE component differs between the marques.

Porsche 9RD Engine

The company says they based their V8 on the one in the Porsche RS Spyder. It displaces 4593cc, has two turbochargers and runs more than 8000 rpm.

BMW P66/3 Engine

This V8 is based on the one used in the BMW M4 DTM in 2017-2018. It displaces 3999cc, has a twin turbo and runs at a max of 8200 rpm.

Cadillac Engine

The GM Performance and Racing Propulsion Team developed this power plant. It displaces 5.5 liters and is the only naturally aspirated engine in GTP competition. Cadillac said it is not a derivative of the LT6 used in the Corvette Z06.

Acura Engine

The company designed this engine from scratch. It displaces 2.4 liters, has a twin turbo, and is the only V6.

How Do They Power the Electric Motors?

All manufacturers use a common gearbox casing and internals produced by Xtrac. This incorporates a Bosch motor generator unit (MGU), which creates power that gets sent into the battery for storage.

How Have the Hybrids Held Up So Far?

At nearly the halfway mark, BMW and Porsche have had issues with the electrical component of the hybrid system.

Porsche lost 35 minutes to replace a battery on its No. 7 car after five failure warnings. IMSA, who receives notifications of the warnings, will pull a car into an area near pit road to assess the cause. The team could not determine if it was caused by a hardware or software issue, so they swapped batteries.

BMW’s No. 25 had had two issues. The first one occurred when the engine stopped running. They couldn’t find the cause, so they replaced many components of the hybrid system, losing two hours. Then, they encountered another issue with failure warnings. They remedied by fixing a loose connection.

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Comments
Caperix
Caperix Reader
1/29/23 8:59 a.m.

I wonder how the motor/generator is integrated into the transmission?  What type of transmissions are they using?  I always felt like Hondas IMA hybrid system would be fun use in a project.

Aaron_King
Aaron_King GRM+ Memberand PowerDork
1/29/23 9:44 a.m.

It seems like Acura is using IMSA to do an extended stress test of it's new for next year Indycar engine.

sleepyhead the buffalo
sleepyhead the buffalo GRM+ Memberand PowerDork
1/29/23 11:13 a.m.

In reply to Caperix :

How Do They Power the Electric Motors?

All manufacturers use a common gearbox casing and internals produced by Xtrac. This incorporates a Bosch motor generator unit (MGU), which creates power that gets sent into the battery for storage.

I think it's a little different to/from the Honda IMA, in that the MGU is on the "transmission side" of the "clutch", so that the car can be driven by MGU without the ICE running?

also:
Thanks J.A.!  I appreciate the detail!

J.A. Ackley
J.A. Ackley Senior Editor
1/29/23 12:11 p.m.

OK, more on the MGU and the electrical end of the hybrid system (ERS) - I have the rule book in front of me.

5.3.2 MGU

a. Position: P2 Off-Axis mounted to front of gearbox with integral gear mesh to clutch shaft
c. Gearing from MGU output to the clutch shaft will be interchangeable to allow for the different behaviors of the various ICE units in service.
d. MGU Package integrated inside the bellhousing and mounted to common gearbox.

To answer your question, sleepyhead:

5.3.11 ERS Operational Modes Supported

a. ERS System is capable of supporting the following operation:

i. Regen: Braking Only, Off-Throttle, Traction Limited, Free subject to equity model constraints

ii. Deployment: Driver Initiated (Conditionally Limited), Free subject to equity model constraints

iii. Limp-home mode (driving at limited speed with ERS-only) subject to equity model constraints

iv. ERS only usage in pitlane subject to equity model constraints and sporting regulations

What's an equity model?

5.3.10 ERS General Performance

a. The performance of the Hybrid System will be controlled by the standard Hybrid Control Unit. A range of input parameters will be used, via a standard Equity Model, to determine the instantaneously available energy and power. These parameters include (but are not limited to): cooling system performance, power request and battery SoC. For further information refer to Hybrid System Documentation Package.

DirtyBird222
DirtyBird222 PowerDork
1/30/23 10:48 a.m.

Maybe I missed it; but, why do they have to all run the same hybrid systems? Seems counterintuitive for having manufacturers developing hybrid race cars to have to use something the series deems mandatory and allows for more nefarious things like nepotism in winning the contract for that system. I.e. why aren't the manufactuers devloping their own hybrid systems in these cars? Testing out tech that they can pass on down to the pedestrian cars? 

Personally, if I were someone like Penske, I'd be pissed if my car lost time on track to something of the sort. 

pheller
pheller UltimaDork
1/30/23 11:10 a.m.

67hp? Weak.

 

Compare that WRC where they are running entire transfer stages electric-only with a electric motor mounted forward of the rear diff, and the driveshaft mounted electric motors generate 134hp which is required to be used in every stage. 

 

If IMSA wants to get serious about this they should require that pit lane is electric only, or offer some sort of bonus laps for cars that run entirely under electric power for an entire lap. 

J.A. Ackley
J.A. Ackley Senior Editor
1/30/23 12:43 p.m.
DirtyBird222 said:

Maybe I missed it; but, why do they have to all run the same hybrid systems? Seems counterintuitive for having manufacturers developing hybrid race cars to have to use something the series deems mandatory and allows for more nefarious things like nepotism in winning the contract for that system. I.e. why aren't the manufactuers devloping their own hybrid systems in these cars? Testing out tech that they can pass on down to the pedestrian cars? 

Personally, if I were someone like Penske, I'd be pissed if my car lost time on track to something of the sort. 

Yes - the same hybrid system for all, but from my understanding, but percentage used differs by manufacturer.

One of the greatest difficulties I heard was mating the electric component with the ICE component. 

j_tso
j_tso Dork
1/30/23 1:54 p.m.
DirtyBird222 said:

why aren't the manufactuers devloping their own hybrid systems in these cars? Testing out tech that they can pass on down to the pedestrian cars? 

That gets really expensive and IMSA is about containing costs.  Spec system gives everybody something to play with without outspending the other guy.

Porsche was spending close to an F1 budget on their 919 LMP1 and they didn't want to keep doing that.

DirtyBird222
DirtyBird222 PowerDork
1/30/23 2:01 p.m.
j_tso said:
DirtyBird222 said:

why aren't the manufactuers devloping their own hybrid systems in these cars? Testing out tech that they can pass on down to the pedestrian cars? 

That gets really expensive and IMSA is about containing costs.  Spec system gives everybody something to play with without outspending the other guy.

Porsche was spending close to an F1 budget on their 919 LMP1 and they didn't want to keep doing that.

Makes sense in that aspect. I'm curious what the payoff is then. It seems like they GTPs were pitting at the same interval as they were last year for fuel. 

I haven't read the rule book so, not sure if the fuel capacity went down and the hybrid system is picking up in that deficit. 

I guess I'm really failing to see what the benefit of this complex hybrid setup is providing for the series or these teams. 

j_tso
j_tso Dork
1/30/23 4:22 p.m.
DirtyBird222 said:

I guess I'm really failing to see what the benefit of this complex hybrid setup is providing for the series or these teams. 

I'd guess marketing, which I still think is where the racing budget comes from. OEMs want to boost their EV/hybrid street cred.

I don't see the point either unless it's like the LMP1's 4WD electric boost which made the cars launch out of the corners.

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