Anyone use a SMALLER intake tube?
 

Would using a smaller diameter intake tube help mileage any? I figure lees air ,and the ecm would compensate for it and use less gas. this would be on a regular f.i. car

You'll just depress the pedal further for the same amount of power, which could decrease the pumping losses from the throttle being open wider. Otherwise, just go slower, and you won't have to make mods to your car for the same gains.

Ok, but what if you consistently run,say, at 60m.ph., for a long distance. Because the diameter is smaller, wouldn't intake velocity pick up some?

The only way you will know is to try it. Make very careful notes, because odds are there will be no difference. The only time it will make any difference is at wide open throttle. Most cars spend very little time at wide open throttle.

Most cars benefit from a larger air intake, preferably one with a cold air feed. You're not going to do it any favours by suffocating it. Think of a car as a human, a smaller intake is like having asthma, with restricted air you're going to breath quicker and more often. With a larger airway, you'll breath easier, deeper and less often.

The intake velocity will pick up in order to provide the required air. With no other changes, the engine is going to need to burn the same amount of fuel at 60mph, and thus need the same amount air, regardless of the intake size.

The airflow can go from smooth laminer to turbulent with a narrower tube. I can't say what effect, if any this will have.

Warm or hot air intakes have shown some efficiency improvement in fuel economy. Warmer air is less dense, so there is less of it for a given volume. With less air in the cylinder, less fuel is added. The power output goes down with the less fuel, but if you do apply more accelerator to make up for it, the throttle opens wider, which lowers the pumping losses in the engine.

Whether it works or not is model dependent, and requires testing.

:thumb: i agree

One of the mpg enhancements Honda used on the VX model was a smaller diameter intake tube as well as a smaller diameter exhaust. Better velocity and turbulence worked well in conjuction with the lower lift of one intake valve, allowing AF ratios as high as 25 to 1.

Intake tube maximum diameter, just like the diameter of header tubes is only effective at maximum power and air flow. A human can breathe through a straw, but running 100 yard dashes would be catastrophic. Higher air velocity increases turbulence and improves mixture homogenity.

Also remember that there is a maf sensor in the intake and if it is not reprogrammed to the new size it will think the increase in air velocity is actually more air and try and keep the air/fuel ratio the same and therefore over fuel. Then the oxygen sensors will see the excess HCs in the exhaust and try and pull it back. This will cause a lean condition which may ping. Some ware along the CEL is bound to come one because it will all be out of balance

A larger intake will essentially be the opposite with the same probability of a CEL.

Now with proper programming to accout for the intake volume some gains can be had.