Marshall Pruett's Tech Mailbag for March 7

Friday, 07 March 2014
submit to reddit

Welcome to Marshall Pruett’s new Racing Tech Mailbag on We had so may questions for the first edition that we had to run this in two parts!

If you have questions about the technical side of the sport for Pruett, who spent most of his life working as a mechanic and engineer in open-wheel and sports car racing, send them to
This email address is being protected from spambots. You need JavaScript enabled to view it.
">This email address is being protected from spambots. You need JavaScript enabled to view it.. We can't guarantee your letter will be published, but Marshall will always reply.


Great to hear 500 champ Jacques Villeneuve is returning to Indy. I read that he will be driving a car that Schmidt/Peterson purchased from Dragon Racing. Are you aware of any other DW12 chassis that have been raced by multiple teams?
​Chris R., Stroudsburg, Pa.

MP: Yes, Chris, DW12s do trade hands, and Dallara has also sold a few news cars since the first batches were released in 2011 and 2012. My man Stefano DePonti from Dallara USA helped with this answer:

"A good example of this is Lotus bought three cars from us, then they were bought from Lotus by teams like [Buddy] Lazier. HVM had a chassis that he brought to Andretti last year. Dragon bought a chassis and now Schmidt bought it like you say, so it is sold three times now. Conquest bought a chassis from us and used it once at Indy, then it was purchased by Andretti. We don't get involved in those sales, but the teams sell to each by themselves."
Pruett Hybrid Porsche

I'm curious about the safety aspect of the electric hybrids. With high amperage batteries, and super capacitors, is there a risk of shock for corner workers & drivers (in a crash that heavily damages the car)? Also, what are they doing to minimize the risk to mechanics? I haven't heard of any problems, but I hope that continues to be the case.

Randy Word

MP: It's a tricky subject, Randy. Hybrid P1 cars are required to have a simple green or red light next to the external kills switch for workers (and anyone else) to monitor whether the system has been discharged and the car is safe to touch. But what if that part of the car is damaged in a crash? There's also a green/red light system in the cockpit, so that's a backup, but in the event of a "big one," you're always going to be concerned about being the conduit for anywhere between two and eight Megajoules of energy.

Corner and workers and safety personnel are trained on dealing with Hybrid cars, just like they are with the non-Hybrids, so that's a plus, and Hybrid teams have hand-held monitors they use to check the discharge when the cars are stationary. This information can also be acquired through telemetry when the cars are on track.
I reached out to my man Owen Hayes, Porsche Motorsport North America's director of operations who oversaw the manufacturer's 911 GT3 Hybrid program (that Hybrid knowledge went into the new 919 P1 car), and asked him to go describe their safety measures in greater detail:

The subject of protecting people around hybrid cars is a subject that is obviously taken very seriously by Porsche. I have also attached a "fire brigade and track marshals instruction sheet" [click here to view by PDF] which we distributed in the past to brief track personnel.

Working on the car: If someone is working on the car, the hybrid system is fully discharged and
that's why you see the red and green signs on top of the cars. Red means the hybrid system is still charged. Green means the system is fully discharged. However in case of someone inadvertently opening a high voltage connector, the high voltage cabling has an electrical protection circuit which monitors and detects the opening and closing of the high voltage connections. If a connector is opened when the system is charged, this is detected by the control unit and the hybrid control unit opens a main relay in the inverter of the energy storage, immediately cutting off high voltage to the vehicle wiring.

There is also what we call an insulation monitor fitted to the car, the function of which is to constantly diagnose the high voltage insulation/shielding. If an error occurs, this is detected by an "isolation switch" and the main relay in the inverter is opened, thereby immediately cutting off the high voltage to the vehicle wiring.

Visual indication: With the GT3 R hybrid for example, the hybrid system operating mode was indicated by red lamps at the front and rear window. When the hybrid system was active, both the front and rear lamps were switched to red on at a voltage above 50 volts. As soon as the hybrid system was switched off, the red lamps would fade out when the voltage went below 50 volts. There were also LEDS fitted to the voltage inverter, so once again if the voltage is above 50 volts, the lamp was red, below 50 volts, the lamp was green. Below 50 volts is not harmful to us humans!

Crash situation: If a crash is detected via an acceleration sensor, the hybrid control unit will immediately shut down the hybrid system and cut off the high voltage to the vehicle wiring.

Emergency off switch: If the car stops on track and the hybrid system has to be discharged, the
outer emergency switch can be pulled which shuts down the entire vehicle and hybrid system. In addition, the fire extinguisher is activated.

submit to reddit

Video: The Champions Issue

The Champions Issue is on sale now. Click here for more information.


RACER Presents: The Bentley Boys' Season-Closing Victory


Robin Miller's IndyCar "fireside chats"


TUDOR United SportsCar Championship: Interviews and insights from Marshall Pruett.

Like us On Facebook

Twitter Feed

racer daily bulletin icon