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Does larger snorkel (air intake) really make any difference?

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I would classify myself as a real beginner regarding motorcycles and physics is not my strong suit, so maybe someone could explain this to me. I have installed an EJK, FMF Q4 and K&N air filter, but I also see plenty of people talking about either removing the snorkel or installing a wider one with a bigger hole for increased airflow. But when I look at the CRF250L I see that the throttle body is smaller in diameter then the actual diameter of the stock snorkel, so how would a larger hole/snorkel increase air intake when the current stock sized hole and snorkel already is larger than the throttle body ?

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It is on almost every bike/atv. My atc250r has almost a 80mm hole that filter and tube, but stock it has a 34mm carb.

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I'm not an expert, but I know that a lot of R&D has gone into air box design over the years.  

IF the diameter of the TB and the snorkel was the same, the velocity of the air going into/out of the air box would be the same.  The larger that snorkel opening is the lower the velocity going into the air box.   Apparently if it is too low (hole too big) you lose some of the desirable characteristics of an airbox. If it is too small you lose HP.  

 

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TB air flow velocity & volume, has a lot more to do than simply the hole size.  Similar constraints to modern muffler designs, the CRF airbox and snorkel were not designed for maximum flow possible through the stock TB, they were designed for sound deadening, some resistance, and adequate flow for the stock bike.  I believe it has been found that the stock TB will flow more air as needed if there is less restriction introduced at the airbox. 

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I am fortunate that I have a pro ArenaCross mechanic that works on and sets up my bike. Tracin removed my snorkel and that was it. He is very good and they even won the 2015 championship ... :thumbsup:   TUF Racing and Kyle Regal .... :banana: 

Tracin in the middle and Kyle is on the right. 

AX041515_3.jpeg

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if  you increase the input into the airbox you are increasing the air volume in the box, which gives the throttle body more air to pull from. at some point  you could make the opening in the airbox TOO large and you'd stop sucking air in through input into the box....but I'd imagine you'd have to get a pretty stinkin large hole before that happened.

 

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1 hour ago, Crapflinger said:

if  you increase the input into the airbox you are increasing the air volume in the box, which gives the throttle body more air to pull from. at some point  you could make the opening in the airbox TOO large and you'd stop sucking air in through input into the box....but I'd imagine you'd have to get a pretty stinkin large hole before that happened.

 

Once the snorkel diameter is large enough to supply all the air needed without acting as a restrictor, increasing its size is of no benefit.   Back to the original posters' question is why would that diameter need to be larger than the TB?  He's wondering why a 36mm hole in the tb requires more than a 36mm hole in the airbox; how does more air pass the smaller hole in the TB?   The answer is in the velocity of that air.   The larger the pressure differential between the input/output the more flow you get through a given diameter.

A fire hose at 1psi doesn't flow near as much water as a fire hose at 60psi.   A 3/4" garden hose at 80psi flows more water than a fire hose at 1psi despite the vastly different diameters.

The pressure differential between the combustion chamber and the air box is large when the intake valve opens (lots of flow through a small opening).   The pressure differential between the atmosphere and the inside of airbox is much smaller.   The smaller pressure differential requires a larger orifice to flow the same amount of air.

 

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Yup, easy to test. Leave the air box cover off and go for a rip. If it has more power, the snorkel is a restriction. If no more power, the snorkel is fine.

 

Or just take the snorkel out and be done with it.

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