My argument against Short-Ram intakes.

Another member asked a question about the advantages of running a snorkel, which really got my gears turning.

A ram air intake, like the majority of the "cold-air intakes" marketed by companies such as K&N, AFE, AEM and Volant is usually a "short-ram", meaning that it looks something like this.



It is using the principle that a less-restricted airflow, compounded by "ram air", which is air being forced into the intake manifold via the movement of the vehicle, AND that cold air contains more oxygen is advantageous for fuel economy and power, which it is. However, if you really analyze what a short-ram air system is, it isn't this at all.

For instance, all of your ambient air is being forced through the radiator and condenser coils, were it is absorbing heat.

Compounded by that, the air pressure at this location is below ambient pressure, so forget about the "air ram" aspect. While one could argue the pressure drop could help even out the effects of the high-temperature air coming in (pressure and temperature correlate with each other identically, as in, the lower the pressure the lower the temperature), however, you still have proximity heat from the engine.

So, what does that mean? Your short-ram cold-air intake is actually a warm air intake. Warmer air is less dense, therefor it contains less oxygen and is less combustable. Your engine compensates for this by opening the throttle wider, and taking in the same amount of air and burning the same amount of fuel, but with less friction, which increases fuel economy at the loss of power.

My point is this- it is impossible for an intake of this type to produce HP gains in a normally-aspirated modern engine, because the engine, electrically, is going to compensate for the change.

So why pay $250+ for a slight difference in engine sound?

Someone change my mind.

 

That particular intake in the picture shouldn't be called a cold-air intake. A cold air intake should pull air in from outside the engine compartment..such as in the fender-well or behind the front bumper.

I agree its not worth the money. If you actually put those on a dyno and did a real test the HP gains would be minimal.

 

x2!!!!!!

go with a "cai" if you want more engine sound........, otherwise.......stick with stock intake and a good filter.

 

Very good and thought out post.... except for this.

The throttle doesn't open wider. The ECU compensates by reducing timing and/or pulls fuel from that map's load cell when there is warmer air (less dense). It does the opposit when the air is cold (more dense).

Unfortunatly, aftermarket intakes on alot of NA engines make minimal gains if at all. And it seems like toyota already made the 4.0L's stock intake pretty efficient. I'm just goin to do a K&N drop-in filter for this reason.