Dear Ralph: With the hood up on any of the F7s I’ve looked at, if you crack the throttle the accordion dryer vent hose...

Dear Ralph:
With the hood up on any of the F7s I’ve looked at, if you crack the throttle the accordion dryer vent hose on the airbox collapses some. How can this be good for performance?

Don Lastrem

Tell me, how often do you ride your sled with the hood up? That expansion joint tube between the intake up in the hood and the airbox down in the belly pan has the flex feature so you can open the hood. When the hood is closed, that tube is not expanded and it doesn’t collapse. Take the tube off at the top, let it collapse just like the hood is closed, then try to compress it like what you saw with the hood up. When the tube is collapsed, the weaker expansion joints are now horizontal and the tube is actually quite strong. This isn’t a problem. The only thing we know to work on this intake is installing a larger inlet snorkel on the airbox if other mods are being made (exhaust, porting, cylinders). On a stock sled, don’t bother.

Also, when the sled is running there is some pressurization of the intake occurring with it out in front of the windshield up on the nose of the sled. Adding any sort of underhood intake undermines the benefit of the cold air (pressurized) intake and tuned tract length. Cat did a good job with the volume and length of the design, most everyone has come full circle with this one. Dyno operators are learning this is an important factor they sometimes don’t replicate when testing, as this intake design needs the airflow over the hood to replicate real-world conditions and airflow volumes. Just because a sled does something with the hood up doesn’t equate to what it will do out in the field. One must replicate, as much as possible, the field conditions. The closer one gets, the more accurate the data acquisition. All static tests are just that; static. What we’re more concerned and interested with how it works on the snow, in real world usage.

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