40 mpg trans am
08-01-2011 | 07:27 PM
#81
Teching In
Joined: Aug 2011
Posts: 10
Likes: 0
Sorry to be harsh, but someone needs to knock some sense into you.
You say you're gonna be an engineer. Well here's some physics for you. An fbody is a 3500 lb car. If you subtract 800 lbs you get 2700. 2700 divided by 3500 is .79 or 79%. F=ma, so if you have 79% of the original mass, you will only need 79% of the original force; its proportional. Lets assume for simplicity that fuel consumption is proportional to power output. At identical speeds, power is proportional to force at the rear wheel. So fuel consumption is proportional mass. Fuel consumption is the reciprocal of fuel mileage(gallons per mile instead of mpg) so fuel consumption would go from .05 gpm (20 mpg) to .04 (25 mpg). Of course this is city fuel mileage and highway is generally much higher. Let me also say that drag racers have removed everything from these cars (lights, mirrors, everything in the interior but the driver's seat, power steering, power brakes, and countless other things you need for the street) and still not saved anywhere near 800 lbs. Expect to buy a lot of carbon fiber.
In city driving, fuel is used mainly to accelerate, which is why we used f=ma and ignored friction. On the highway, your mileage is better because you hold constant velocity (eg a=0 so F also is 0). Force is instead being used to overcome rolling resistance and aerodynamic drag. Drag increases with the square of speed, so you literally have 10 times as much drag at 65 mph as you do at 20. Drag is independent of weight, so your fuel mileage probably won't see a noticeable change. You will have slightly less rolling resistance, but believe me you can gain more by pumping up your tires. So expect 30 mpg highway to go to 31 (and believe me this is optimistic).
On to the motor. If heating fuel or putting hydrogen in the mixture did ****, manufacturers would do it from the factory. Toyota did not put millions into hybrid r&d if heating fuel would make a prius get 50mpg. In all of these systems, you put more energy in than you get out.
Lastly, turbos don't directly improve fuel economy. Forced induction does nothing when the throttle body is closed and you are purposely restricting intake airflow to prevent the car from running away on you. You gain mileage with a turbo because a smaller engine can make the same hp as a naturally aspirated big engine. A twin turbo ls1 will suck just as much, if not more fuel.
I'm not against the project. Just remember that this is a hobby and by no means an investment. Even if you could get 40 mpg, it would take 100,000 miles of driving to recover a $10,000 investment. If you want to go through with it an exhaust will help power and fuel economy. Lowering the car and side skirts will cut drag, helping fuel economy and high speed acceleration slightly. !antenna and anything else not smooth on the body. You can also tune it a little lean, but be warned, you may seriously hurt engine life if you go too far, and power will suffer. I'd love to see a high power, high mpg f-body. If you lower your mpg goals a bit, its a great project.
You say you're gonna be an engineer. Well here's some physics for you. An fbody is a 3500 lb car. If you subtract 800 lbs you get 2700. 2700 divided by 3500 is .79 or 79%. F=ma, so if you have 79% of the original mass, you will only need 79% of the original force; its proportional. Lets assume for simplicity that fuel consumption is proportional to power output. At identical speeds, power is proportional to force at the rear wheel. So fuel consumption is proportional mass. Fuel consumption is the reciprocal of fuel mileage(gallons per mile instead of mpg) so fuel consumption would go from .05 gpm (20 mpg) to .04 (25 mpg). Of course this is city fuel mileage and highway is generally much higher. Let me also say that drag racers have removed everything from these cars (lights, mirrors, everything in the interior but the driver's seat, power steering, power brakes, and countless other things you need for the street) and still not saved anywhere near 800 lbs. Expect to buy a lot of carbon fiber.
In city driving, fuel is used mainly to accelerate, which is why we used f=ma and ignored friction. On the highway, your mileage is better because you hold constant velocity (eg a=0 so F also is 0). Force is instead being used to overcome rolling resistance and aerodynamic drag. Drag increases with the square of speed, so you literally have 10 times as much drag at 65 mph as you do at 20. Drag is independent of weight, so your fuel mileage probably won't see a noticeable change. You will have slightly less rolling resistance, but believe me you can gain more by pumping up your tires. So expect 30 mpg highway to go to 31 (and believe me this is optimistic).
On to the motor. If heating fuel or putting hydrogen in the mixture did ****, manufacturers would do it from the factory. Toyota did not put millions into hybrid r&d if heating fuel would make a prius get 50mpg. In all of these systems, you put more energy in than you get out.
Lastly, turbos don't directly improve fuel economy. Forced induction does nothing when the throttle body is closed and you are purposely restricting intake airflow to prevent the car from running away on you. You gain mileage with a turbo because a smaller engine can make the same hp as a naturally aspirated big engine. A twin turbo ls1 will suck just as much, if not more fuel.
I'm not against the project. Just remember that this is a hobby and by no means an investment. Even if you could get 40 mpg, it would take 100,000 miles of driving to recover a $10,000 investment. If you want to go through with it an exhaust will help power and fuel economy. Lowering the car and side skirts will cut drag, helping fuel economy and high speed acceleration slightly. !antenna and anything else not smooth on the body. You can also tune it a little lean, but be warned, you may seriously hurt engine life if you go too far, and power will suffer. I'd love to see a high power, high mpg f-body. If you lower your mpg goals a bit, its a great project.
