Remove the airbox lid and snorkel?

[adam728]

Those calcs leave out that a 35mm venturi flows much more than a 35mm pipe, and that a 20x80 snorkle has much more turbulant flow due to the much larger wall perimeter to area than a round pipe. What the snorkle does have going for it is that the airbox acts as a plenum, so its peak air velocity due to engine pulses is lower, things are balanced out a bit.

[Julien D]

Honestly that calculation leaves out quite a bit, as its designed with liquid flow being pumped through pipes with or without fittings. Doesn't account for filter, carb, reeds, or combustion engine airflow in general. I don't really see the relation.

[Jaguar]

that calculator is for liquid or gas. depends on the viscosity and specific gravity that you input.

the point is that each component (reeds, carb, filter, airbox intake) have a restriction to flow and its best to know what that is for each component. The filter has a restriction but you don´t throw that away because it has a useful function. So does the airbox lid and snorkel. the reed valve is very restictive but works fairly well without complexity. (I prefer a rotary valve) The idea is to have the other components other than the reed valve have less restriction than it, which is the case with this well designed bike.

[adam728]

that calculator is for liquid or gas. depends on the viscosity and specific gravity that you input.

the point is that each component (reeds, carb, filter, airbox intake) have a restriction to flow and its best to know what that is for each component. The filter has a restriction but you don´t throw that away because it has a useful function. So does the airbox lid and snorkel. the reed valve is very restictive but works fairly well without complexity. (I prefer a rotary valve) The idea is to have the other components other than the reed valve have less restriction than it, which is the case with this well designed bike.

But I'm saying you don't know what it is for each component. A carb ventrui will flow more than a straight pipe of the same diameter. A rectangular snorkle will flow much less than a pipe of the same cross sectional area. Imagine that 20x80mm opening being 2x800mm. Cross sectional shape has a huge effect on airflow. Especially when you are making direction changes.

It's far to simplified to claim based off those calcs that removing the snorkle or lid won't make a difference.

I now have a DR650. I'll have to look up the numbers, but I am certian the snorkle has more area than the carb. I am also certian I gained a good amount of power pulling the snorkle, and had to richen the needle as it had a lean hesitation after pulling the snorkle. Somewhere out there is even a dyno showing 2-3 hp by cutting the top off the airbox, good jetting before and after. I didn't cut yet, as I want to go back to stock and work my way step by step when I get time to install my wideband setup.

Not the same as a KDX I know, but I bet your calcs would show the snorkle not being a resteiction on that bike as well, and it's well documented that it is.

[Julien D]

I realize the calc is built to handle liquid or gas when you are pumping it at a constant rate through a set of static sizes of pipes and fittings. That setup does not at all describe the air/fuel intake system on a combustion engine, 2 stroke or otherwise. The only way to get accurate measurements on this would be with a bench flow test.

[Jaguar]

So if your quirks have some validity and we say it is twice as bad as what the calculator shows then we are still only talking about a pressure drop of .1psi, next to nothing.
People should be focusing on jetting the bike right instead of throwing away important parts.

[flightmare]

C'mon, this isn't the big bang theory .
Toss that lid, make a cardboard lid that covers about 1/2 of the box opening and bend the last 1/2 inch up to make a water deflector .
have made several over the years.
New Honda cr's cane with cardboard deflectors in the 80's and 90's
Just need a cereal box, scissors and stapler .
If done correctly, the seat holds it in place.
Try it.

[Julien D]

The primary purpose of that part is noise reduction, and it does indeed perform that function pretty darn well. So if that is important to you, keep it. As for the calculator, I am not saying it is questionable, I am saying that you are using for an application completely outside of what it is designed for. So the results are not half, or part, or any other measurable amount off, but completely unrelated.

In all honesty, this discussion has come up dozens and dozens of times over the years. To my knowledge, nobody has ever had an issue running without the lid, or with it. So whatever you prefer is fine. :)

[Jaguar]

saying a flow calculator is unrelated to the intake flow of a motorcycle is like saying a speedometer is unrelated to velocity.
granted, the flow with a motorcycle is pulsating but still the calculator gives relevance.
A happy medium between the two extremes is to discard the stock snorkel and make a less restrictive one to replace it. But I would never recommend someone just doing without one. They serve a useful purpose.

[Julien D]

I understand your point of view, but I respectfully disagree. It's best use is as wall art.

[bufftester]

I understand your point of view, but I respectfully disagree. It's best use is as wall art.

lol...not very good wall art tho!

This thread is a great example of theory vs. reality. Theory will get you close, but there's a reason why you test actual hardware instead of just using the numbers. The assertion that the snorkel is an important piece of the intake tract that was thoughtfully constructed and integrated to maximize performance of the bike is laughable. The KDX was born of KX roots, and a MX bike IS designed for max performance...and they dont come with snorkels or air box lids beyond the seat and body plastics. The lid on the KDX serves the primary function of reducing the noise, with the benefits of "waterproofing" really a secondary accidental happenstance. Real world numbers bear out that removing the lid and rejetting will give you more performance gain than leaving the lid and rejetting. The spark plug thing isn't even worth the effort of typing. A hundred years of experience show that providing the max possible air flow, with the minimum amount of disturbance gives you teh best performance. Some things you absolutely have to live with...filter, reed cages...others you dont...lids. And as for washing your bike...1. There are areas you should never be directing water, airbox is one, just like you don't hose out your pipe. What little water does get in there will drain out the valve in the bottom of the airbox (you have checked it to make sure it's clear and functional, right?).

At the end of the day the bike runs great whatever configuration you choose to use as long as you take the time to rejet it properly. Use what makes you happy. And if you're riding somewhere where drowning the engine is that huge a concern you may want to trade your bike for a jetski lol

[Sullyfam]

And with that, I'd like to officially declare this horse beaten. beyond death!


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[KDXohio]

[Julien D]

And with that, I'd like to officially declare this horse beaten. beyond death!


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I think that happened years ago, lol.

[Gotanubike]

Mine stays on(with a botched snorkel and holes cut in the air box(thanks to previous owner) but: