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Note,
A fire extinguisher is a time buying tool, if it puts out the fire completely, all the better. A Porsche engine is aluminum(or magnesium) filled with almost 3 gallons of oil. Said oil resides in the engine compartment and is held in the tank with rubber hoses. Halon and the derivatives will simply not be enough, especially if gasoline is involved as well. Dry chemical, preferably Purple K is the tool of choice for a potential metal fire, yes aluminum will burn in the right conditions as well. The best suppression system is in the engine compartment and remotely actuated or automatic. Ultimately fire fighting is salvage after the lives are saved. I carry a 2.5 lb Purple K extinguisher on the front of the pax seat. Those small halon style glovebox extinguishers won’t do much. The preferred firefighting method for engine fires is a water deluge from a inch and a half hose and a couple hundred gallons of water or next, dry chemical, followed by whatever you have.
The fire dept I worked for had several large Purple K extinguishers on my engine. They were only deployed if the engine fire involved burning metal otherwise we would deploy a water hand line with a sheet metal lance nozzle. Halon or other gaseous agents will dissipate rather quickly due to them being heavier than air. If carrying a glove box halon type bottle makes you feel better, go for it, just adjust your expectations accordingly.