venting engine bay - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

g6civcx · 11-25-2008, 06:49 AM

I'll try to flashback to my motorsports engineering classes from 15 years go.

I realised from the beginning that aero is pretty much pure speculation. You either have to rent a full scale wind tunnel to the tune of $10k per hour, rent a smaller wind tunnel and build a scale model, or at least do computer simulation.

Everything else is pure speculation. That's why I stuck with digital control systems.

Trying to move air molecules is like trying to herd a group of very antisocial and lazy people. When you group them together, they try to spread apart as much as possible via the path of least resistance.

Air will try to move from areas of crowding (high pressure) to areas with open space (low pressure).

When a car is traveling through air, the highest areas of pressure are 1) the leading edge of the bumper, and 2) the base of the windshield.

Any time you try to separate air layers and puch a hole through the air you will get resitance.

Airplanes try to make the fuselage as pointed as possible to reduce drag. Also, "sports" cars have steeply raked windshields to reduce drag as well.

Generally, in order for air to move through the radiator fins, you need to create an incentive by putting a low pressure area directly behind the radiator. You can do this with a fan, and/or by blocking all other paths of travel with cooling panels.

Once air is in the engine bay, it needs to leave. You can use undertrays to create a venturi effect and force the air to travel between the engine and the undertray. This can also create front end lift as the air travelling below the car lifts the front end.

The other area is the base of the windshield. If you cracked the hood open, the area under the hood near the valve cover would have low pressure. The air would go from the high pressure area of the base of the windshield into the valve cover area. Then where would it go?

If you have your intake where the valve cover area is, which is where Chevy small blocks do, you can take advantage of the ram air effect and suck in more air into the carb. Otherwise air would stall around the underhood area and run into each other.

Again, these are just generalizations, and it depends on the specific design of the car. Nobody is right and nobody is wrong. It's just opinions.

11-25-2008, 06:49 AM	#21
g6civcx Post Whore! Join Date: Apr 2004 Location: Virginia, USA Posts: 5,764 Trader Rating: (5) Feedback Score: 5 reviews	I'll try to flashback to my motorsports engineering classes from 15 years go. I realised from the beginning that aero is pretty much pure speculation. You either have to rent a full scale wind tunnel to the tune of $10k per hour, rent a smaller wind tunnel and build a scale model, or at least do computer simulation. Everything else is pure speculation. That's why I stuck with digital control systems. Trying to move air molecules is like trying to herd a group of very antisocial and lazy people. When you group them together, they try to spread apart as much as possible via the path of least resistance. Air will try to move from areas of crowding (high pressure) to areas with open space (low pressure). When a car is traveling through air, the highest areas of pressure are 1) the leading edge of the bumper, and 2) the base of the windshield. Any time you try to separate air layers and puch a hole through the air you will get resitance. Airplanes try to make the fuselage as pointed as possible to reduce drag. Also, "sports" cars have steeply raked windshields to reduce drag as well. Generally, in order for air to move through the radiator fins, you need to create an incentive by putting a low pressure area directly behind the radiator. You can do this with a fan, and/or by blocking all other paths of travel with cooling panels. Once air is in the engine bay, it needs to leave. You can use undertrays to create a venturi effect and force the air to travel between the engine and the undertray. This can also create front end lift as the air travelling below the car lifts the front end. The other area is the base of the windshield. If you cracked the hood open, the area under the hood near the valve cover would have low pressure. The air would go from the high pressure area of the base of the windshield into the valve cover area. Then where would it go? If you have your intake where the valve cover area is, which is where Chevy small blocks do, you can take advantage of the ram air effect and suck in more air into the carb. Otherwise air would stall around the underhood area and run into each other. Again, these are just generalizations, and it depends on the specific design of the car. Nobody is right and nobody is wrong. It's just opinions.