Do so-called “cold-air” or less restrictive intakes increase gas mileage? Or do they provide more power at the cost of lower mpg?
I say so-called because I heard somewhere that most modern engines already draw in cold air and the major purpose of an after-market intake is to increase mass air flow. Is this correct?
Thanks!
bump
I did do a search on this topic and while I found that a less-restrictive exhaust increases mileage, I found no evidence for a less-restrictive intake. However, some of my auto-enthusiast friends claim a larger intake increases mpg.
I`m certain the reason for cold air intakes is that the colder the air the more dense it is and the more you can shove into the cylinders. Creating a better fuel/air ratio witch increases the explosive power and bumps up horsepower.
Larger intakes would reduce intake air friction and allow more air into the cylinder, the more air that flows the cooler the engine runs and the cooler the engine runs the more air you can shove into the cylinders, etc.
If you increase the amount of air entering your combustion chamber, then you will have to increase the amount of fuel, or burn a leaner mixture. In the first case, you will increase power produced and lower mileage. In the second case, you will decrease power, and perhaps raise mileage. (A wide variety of factors will determine how much mileage change will occur.) However, your exhaust manifold will have to be “tuned” to allow better flow out of the combustion chamber, and will also get hotter, possibly even burning through at choke points.
In order to really answer you specifically, someone (not me) would have to analyze the fuel/air characteristics of your particular car/carburetor/exhaust set up, and the proposed changes. If it is a stock automobile, it is unlikely that you will be able to just bolt on a mileage improvement. Fleet mileage requirements are pretty tough, and such a system would be at least an available option, if not standard equipment.
In the case of high performance prototype machines, you have to experiment with dynamometers, and fuel use analyzers. In most cases, that involves improving power, or torque, not mileage.
Tris
Only so much air can flow throw the throttle body. If the intake actually limits the airflow to less than that amount, replacing it with a less restrictive one will allow more power to be developed. Once the intake allows enough flow to match the capacity of the throttle body, there is nothing more to be gained with further reducing intake restricition – at that point the bottleneck is elsewhere.
If intake restriction reduced fuel mileage (and I don’t see how it could on electronic fuel injection systems), essentially the same effect could be achieved by limiting how far the throttle opened. How many cars get less mileage at part throttle than at full throttle? Answer – none.
Now, on a carbureted car, certain intake restrictions could have the effect of choking the carburetor, which would cause rich running and reduce mileage. But again, once the intake allowed all the flow the carb could handle, further reducing restriction would have no effect.
Certain stock set-ups might have intake flow that allows all the engine can use, but is somewhat restrictive once the exhaust has been modified to enhance engine breathing. In such a case, enlarging the intake to match the exhaust capability would be called for. I don’t know if such cases actually exist, but I could see it being possible.
I suspect you might get some mileage gains from a well-designed intake not because you’re getting more air into the throttle body, but because the air that’s getting in there is doing so with greater ease. That means less pumping losses, which should lead to marginally better gas mileage. The stock intakes on cars these days are usually pretty efficient though.