Technical Question: Air Flow to Rear-engine - how is it managed?
07-15-2018, 07:58 PM
#1
Rennlist Member
Thread Starter
Technical Question: Air Flow to Rear-engine - how is it managed?
Hi all,
I always wondered HOW the airflow to the rear engine is managed on our cars... obviously there's air vents, plus a massive fan to draw air in... however, it is in the OPPOSITE direction of travel! Meaning, while air is sucked into the engine directly in front engine cars, and even F1 and Indy cars with the air vent on top of the driver, in our cars the air is sucked in at the opposite end.
To me, this is not as efficient as it could be, specially at higher speeds, and a top vent above rear windshield, a vent on the side (like Turbo/Boxster), or a crazy solution like Williams Singer car (rear window vents) would be more effective. What are your thoughts?
I always wondered HOW the airflow to the rear engine is managed on our cars... obviously there's air vents, plus a massive fan to draw air in... however, it is in the OPPOSITE direction of travel! Meaning, while air is sucked into the engine directly in front engine cars, and even F1 and Indy cars with the air vent on top of the driver, in our cars the air is sucked in at the opposite end.
To me, this is not as efficient as it could be, specially at higher speeds, and a top vent above rear windshield, a vent on the side (like Turbo/Boxster), or a crazy solution like Williams Singer car (rear window vents) would be more effective. What are your thoughts?
07-15-2018, 08:11 PM
#2
Rennlist Member
You can make air do whatever you want if you know what you are doing. They actually designed in some air pressure back there. Not much different from how muscle cars had an air inlet in front of the windshield facing backwards.
Also, when the rear wing is up, I believe even more air is sculpted into the intake (or at worst, prevents negative air pressure from accumulating at higher speeds).
Also, when the rear wing is up, I believe even more air is sculpted into the intake (or at worst, prevents negative air pressure from accumulating at higher speeds).
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driggity (10-25-2021)
07-16-2018, 12:18 PM
#3
Air going through the engine is very relative and actually quite limited. Air goes through the radiator and that is about it, on most cars.
On the Carrera, there are two radiators behind the front wheels, used to cool the liquid used for cooling the engine. The fan located on the rear lid is used more to extract heat at low speeds or after parking the car.
There is fresh air coming into the engine compartment, from underneath the car, as the entire area below the engine is open.
Yves
On the Carrera, there are two radiators behind the front wheels, used to cool the liquid used for cooling the engine. The fan located on the rear lid is used more to extract heat at low speeds or after parking the car.
There is fresh air coming into the engine compartment, from underneath the car, as the entire area below the engine is open.
Yves
07-16-2018, 12:59 PM
#4
Rennlist Member
I should also point out that as air flows over a curved surface (our car’s exterior) on one side and meets air that travels along a flat surface (the bottom of our car), lift is generated, which pulls the car off the ground. Now, thankfully, cars are heavy, but as speed increases, the lift is greater. So the spoiler (or wing in some cases) helps reduce rear end lift to keep the rear from feeling and acting loose.
Regardless, there are still some higher pressure arears around the curved surface of the car. Engineers would design air intakes around these pressure areas.
If and when the rear engine compartment gets hot, there is an auxiliary fan that turns on via a thermostat and pulls air from the top through the bottom (reverse of how hot air wants to move, which is up) to help cool the engine bay. Why reverse? Because the car is designed to suck air from the same location. You don’t want hot air being sucked into the intake. And because at speed, air will be forced down through that relatively higher pressure area anyway.
Regardless, there are still some higher pressure arears around the curved surface of the car. Engineers would design air intakes around these pressure areas.
If and when the rear engine compartment gets hot, there is an auxiliary fan that turns on via a thermostat and pulls air from the top through the bottom (reverse of how hot air wants to move, which is up) to help cool the engine bay. Why reverse? Because the car is designed to suck air from the same location. You don’t want hot air being sucked into the intake. And because at speed, air will be forced down through that relatively higher pressure area anyway.
07-16-2018, 02:00 PM
#5
Nordschleife Master
This is a water-cooled car. Air plays no significantly role in cooling the engine; oil and water does. The engine lid fan is there to push air from top down to remove heat from the top heat sensitive parts when the engine is very hot and the car is parked.
07-16-2018, 03:27 PM
#7
Rennlist Member
^^ Correct. Coolant probably cools about half of the engine, and oil cools about half, yet oil itself is cooled by a water-to-oil cooler, so nearly all heat must be removed from the radiators in the front of the car.
The reason why these cars don’t have coolers in back likely has to do with space and weight. There’s just not enough room back there, so they had to move the radiators up front, which adds complexity for sure, not to mention the weight and cost of all those hoses.
That said, the radiator location probably IS the best spot to take in air and coil the car.
The reason why these cars don’t have coolers in back likely has to do with space and weight. There’s just not enough room back there, so they had to move the radiators up front, which adds complexity for sure, not to mention the weight and cost of all those hoses.
That said, the radiator location probably IS the best spot to take in air and coil the car.
