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Hey guys,

Is there anyone out there with some wisdom on airbox design and the importance of volume for a high output 2 stroke. Basically my question is can I run a silicon 2-1 "airbox" like used in boosted applications or will this hinder performance? I don't have the option the run any sort of factory box so please refrain from the suggestion.

Thanks, Joe
 

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From my extensive phone bill recently, the consensus across the MX/Sled/desert racing scene is that an EFI needs some sort of airbox. However big or small is not important, simply that the air has balanced pressure before entering the throttle bodies. Turbo applications aside.

I've run my M7 bigbore without so much of an airbox perse since 2005 so I'm skeptical that it's absolutely needed however since we are talking Doo's and their limited airflow I'm not really taking that experience to heart. I had to come up with a custom airbox for my application. Whether needed or not, I still don't have proof one way or another. Flexible tubing feeds into the gauge pod and draws air from there.

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On the dyno is where you can see how much impact a tuned airbox has. In my opinion, anyone that wants to run more or less of an airbox is free to do so. If this was something that meant a lean condition, then this could be a problem, but this would mean an engineered and tested design that went well above the factory one. I doubt this will ever be a problem.

Some prefer pods while others prefer drilling holes in the back of the airbox. I still have folks asking me if they should run pods and I don't know. I just say to run what they like. It is one of those things that is really low on my list. Those who run them on the dyno or in races know the difference, but I don't see much of a problem for the common owner.

Some of you may remember Steve Laminion's article from 20 or so years back. I tried it, but my hands were already full with working throught the clutching/traction/suspension/skid that I had trouble finding a noticeable difference in the power output. In other words, whatever power gain I had, I also needed to make adjustments to take fruit. Of course back then I didn't have access to the fancy Turbo Dynamic gauge we more commonly see today to evaluate change in performance.

There are just so many things that affect performance. I believe the guy who said he measured a higher output from whatever airbox mod. I have no reason to doubt him. But his sled and my sled are two completely different engines. For example, on the simplest level, cranking compression - or call it ring seal - is a big thing. Without a performance monitor like Turbo Dynamic, it is anyone's guess. Without a Wideband, then it is also anyone's guess if the new airbox or pod mods will provide an improvement in the air intake. And that's not even measuring a changed in air flow which is another big thing.

Since most sleds are not equipped with any monitoring, I say have at it and enjoy the ride.
 

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air-boxes are Helmholtz resonators. http://newt.phys.unsw.edu.au/jw/Helmholtz.html
Try to match stock volume if you are running stock RPMs, I'm not sure what the impact of boost pressure would be on the resonance.

Ps. I tried an old cat fanner with pod filters. That was comically bad. Once warm, I had to flip open the hood to start from a stop. The airbox went back in the same day.
 

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air-boxes are Helmholtz resonators. http://newt.phys.unsw.edu.au/jw/Helmholtz.html
Try to match stock volume if you are running stock RPMs, I'm not sure what the impact of boost pressure would be on the resonance.

Ps. I tried an old cat fanner with pod filters. That was comically bad. Once warm, I had to flip open the hood to start from a stop. The airbox went back in the same day.
This. I think pods would work if not for the warm underhood air. Think a car with ITBS or stack injection, they have a lot of underhood airflow, lack a hood or stick out of the hood into clean cool air. On a sled that limits you to some sort of airbox that you need to feed with outside air. The small silicone box won't work and will kill throttle response since there is no idle volume of air to feed it but they work ok when boost is being shoved through them. Fab the biggest aluminum box you can fit and then feed it with a big tube from outside the hood. Look at the Bondi box for inspiration.
 
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