Quick 2 stroke power tip: "Porting" your stock reed cage

[Billy Golightly]

I recently replaced the stock reeds on my 85 270R Flat tracker with the Boyesen brand "Pro Series" carbon fiber reeds and found that the design of the reed cage was actually blocking off quite a bit of flow that the reeds were actually open for. So I screwed the bottom reed down and took a black magic marker and filled in all the areas that needed material removed for the cage and reed to match each other correctly. I then removed the reed and cut out the black areas with a pneumatic die grinder. You also want to make sure you slope the cuts out ward, and not just flat. It more then likely wont out perform an aftermarket reed valve like a Boyesen RAD valve or V Force. But, its a pretty quick and straight forward mod that costs nothing if your running aftermarket performance reeds. If you don't have a die grinder you could use a file. Nothing to it. I do reccomend as I mentioned angling the cuts out and also matching up the inside plastic "stuffer" to the new outlet tract.

[weed]

hummmmmmmmmmmmmmmmmmmmmmmmmmmmmm

[atctim]

Billy - how do you keep your hands so clean? - Cool tip BTW, let us all know about performance differences with this little mod.

[BigGreenMachine]

Interesting. I was going to ask about porting the stock cage. I didn't think about that area of the cage however. I was wondering what can be done with the back or "entrance" of the reed cage vs. the exit of the cage like you have done Billy.

[Billy Golightly]

Billy - how do you keep your hands so clean? - Cool tip BTW, let us all know about performance differences with this little mod.

All my parts (were) clean and here in the house. Otherwise I'd be one greasy mofo.

Interesting. I was going to ask about porting the stock cage. I didn't think about that area of the cage however. I was wondering what can be done with the back or "entrance" of the reed cage vs. the exit of the cage like you have done Billy.

I did very light "clean up" on the entrance, mostly just knocking down sharp corners. I wouldn't go beyond matching it up the intake boot. Squared off steps and ledges are your main enemy to high velocity flow. If when the cage and boot are bolted together and you run your fingers around inside and feel any sharp edges, or steps/ledges like I mentioned then definitely smooth them out. I also smoothed down the sharp edge/ledge from the plastic stuffer onto the actual aluminum cage at the entrace of each "reed canal" as I call it. This is pretty much just a by product of the manufacturing of the reed cage and the OEMs being unable to spend the time to go in and smooth them out by hand.

Now as far as going further then that, to say totally removing the plastic "stuffer" which you can see in the back of the cage in the first picture there are pretty much 2 schools of thought on it. Keep in mind this is all pretty much in simplified terms for me to describe and even understand myself. Fluid/air dynamics and pulse waves acting in an intake is some pretty freakin hairy stuff mathematically and from an engineering standpoint. I'll describe it the best I can and let you decide.

The first camp believes that the stuffers are there almost entirely as a detuning factor and that the intake cannot flow a high volume with them in place simply from the lack of area. Generally speaking, larger area=more volume. Removing the stuffers makes a larger single area that can be filled with volume without distractions. A cavity, so to speak. If you could make a carb outlet and intake inlet the exact same size as the intake/reedcage flange you'd be way better off is an example of this school of thought.

The second camp believes that the stuffers, acting as just that stuffing the "cavity" increases the volumetric pressure inside the intake and therefore the velocity of the charge entering and leaving the area. Which, in an effect draws more volume too. This camp believes that any large cavities significantly slow the speed of the charge, and also diminishes the strength of the intake "pulse". Now the intake pulse is thought to work pretty much like a 2 stroke exhaust pipe. The shape, diameter, and length of the intake allows it to reflect pressure waves coming from inside the motor (Like how a reed open and closes) and is actually able to create a vacuum and pull in more of a charged mixture. So according to this, the thing that you definitely do not want is a small stuffed intake boot emptying out into a large, open area reed cage.


I'm by no means an expert on this type of stuff but i've done what I would consider a fair amount of studying and reading on these subjects and feel like I understand the concepts pretty well. But- If I've misunderstood or represented something wrong please feel free to correct me.

Edit: Wanted to add, that the first method should, almost always, out perform the second on a flow bench test. But a flow bench and real world use are 2 completely different things

[Liquid-Darkness]

Billy how do you feel the yellow stuffer makes power in your engine? Any paticular area of the power band change when the stuffer is removed/added? I have owned two 85 250Rs now and neither of them had a stuffer like the one pictured in your thread. Should I try one out?

[lndy650]

without a stuffer the reed cage area is much larger than the bore of the carb resulting in a slow moving air/fuel mixture
another thing...If the reed fixing screws protrude into the air stream grind them off flush with the cage if the screws are below the surface fill in the holes

[lndy650]

wow super old post

[BigGreenMachine]

No matter, your tip was a good one.