Pods vs Stock air box

[TopCatGr58]

Hey there Mr. Schweer,

I, too, am not an engineer, carb guru, etc., and I as well as the rest of us welcome the chance to learn something.

Perhaps the term velocity stack is perhaps wrong in this application?

The XS11 is known for having lots of low rpm grunt in OEM configuration, airbox and OEM pipes, 4-2 with crossover pipe. It's also been reported that folks have experienced losses in that low rpm torque when intake and exhaust mods have been made. One of the common mods is putting on aftermarket 4-1 pipes, and they are usually tuned for mid/high rpm type power curves and scavenging and so result in some loss of the low rpm torque.

The other common mod is Indy POD filters vs. the OEM airbox, which also lean out the air/fuel mix and rejetting is often required. The cheap POD filters have the annoying mounting lip that restricts air flow thru the ports in the inlet bell and many folks reported severe loss of ability to get past 5-6k rpm due to this restriction, and even fouling of plugs. I don't recall whether folks having installed just POD filters with OEM exhaust had any problems or changes in their low rpm torque/grunt?

It was noted/observed that the OEM air box inlet tubes to the carbs are actually a bit longer than what is seen on the outside of the carbs/airbox, they extend a few inches INTO the airbox, and that they "MAY" provide a smoothing out of the airflow as well as possibly increased speed/velocity? before the air gets to the carb throat, and perhaps this helps in better atomization of the fuel/air charge going into the engine thru the CV carbs??

It was also thought that using the direct mounting K&N style PODs with no-lip inlet bell non-restrictive mounting might actually contribute turbulence to the air flow coming from all around the inlet bell going into the carb, and that turbulence possibly contributed to a less optimum atomization of the fuel/air mix/charge going into the carbs, and that it might be a factor in the loss of low rpm torque/grunt?

SO...the use of the extended mounting tubes for the cheap filters may more closely act like the long OEM inlet tubes of the OEM AIRBOX and might help to smooth out the airflow, and that this "MIGHT" help with the loss of the low rpm torque/grunt while doing this type of intake mod?

I don't have a flow bench. I did notice a slight reduction in overall throttle response and performance when I had the "lipped" pods mounted directly to the carb bodies, and after using the "extensions", it seemed to regain it's response and power. This in not at WOT, but varying amounts of throttle input across a wide rpm band. This is/was my thinking, but I could be wrong!?
T.C.

[madmax-im]

I have k+n pod filters...I have ridden in rain and have not had any negatives to report from the experience. I am glad that I decided to buy the K+ns' even though they were more pricey than others...no internal lips and have been trouble free for me...even at 1500-2000RPMs' my start offs are pretty sooooth ...

[Mr. Schweer]

T.C., thanks for the clarification. That makes sense as far as (and the term would be correct) the velocity stacks making up the distance that is shortened when the airbox is removed. I believe the main reason for the required length of the boots from the a.b. to the carbs is the tiny air inlet. That tiny little opening goes into the airbox and air is channeled into four separate passages and creates a LOT of turbulence and kills velocity.......sooooo, I believe the extended length might be there to make up for that.
I hope I typed that so it makes sense....(I've had a helluva long/bad day and only running on 1 cylinder myself!!!)
Going back to the velocity stacks with just pods, I still doubt that they would help low-end power in and of themselves. I would guess that the main benefit would be smoothing out obstructions from the lip of some of the more inferior pods.

[Jimmyshifts]

Which Pods Are For Me?

I have a 78 1100. All the ads for pods seem to state they are for 79 and later bikes. What size do I need and where should I get them. My airbox is missing some bolts so I just thought it would be easier to throw on the pods.

Thanks!

[thewiz]

Hey, Jim ...

I bought mine from MikesXS ... although earlier I goofed and said I had bought them from PartsNMore ..... probably the same POD but the ones from Mikes say 'XS' on them and I liked that. Look back in this thread a few posts and see the links form TC. I like mine.

[WMarshy]

Ram air baby!

"
I think that this is about the most wrong statement I've seen in a while. Tunnel rams work at wide open throttle in high rpm applications. They KILL low end torque. The longer tunnel or path creates high engine speed velocity into the cylinder.

I dont believe adding length to the intake runner will result in an increased air velocity into the cylinder, everything I have read indicates:
longer pipe(what have you)=more friction loss=lower velocity... I supose what your getting at is trying to get a more uniform profile entering the carb while using pods..?

Although I haven’t read any specific material on the matter, I’ve had a few indepth discussions with my teammates and my engineering professors about taking advantage of the “ram tunnel” effect from intake runner geometry. My understanding is, the ram affect can be taken advantage of at any RPM given the geometry/length of the intake runner at a “natural frequency” for that specific RPM. In an attempt to elaborate on this so called “natural frequency” Im refer to… When the intake valve closes, the incoming air that never made it past the valve slams into the back of it and reverberates “a puff” of air back out the intake runner. In a perfect world, the “exact” length of the intake runner could be calculated so that this “puff” travels all the way back out of the intake runner and reverbs a second time from the air box and sends a “secondary reverb” back down the intake reaching the valve at the “exact” time it opens. Presto, ram air! In fact, an alumni/earlier team member designed an oil pressure actuated mechanism to control the optimal length of the intake runner at varying RPM. Think infinite step intake runner geometry control at any rpm, kool eh? He even had the dyno data to prove it worked, why we don’t use it on our car now I have no idea! Well like I said I’m far from claiming that I have any knowledge about the subject so feel free to tear this apart if you feel inclined. What I do know, ram air can be taken advantage of at any rpm not just at WOT. Just like we chose the type of header to accommodate low, mid, or high RPM ranges, the intake runner lengths works in kinda the same manner. I would tend to think that our “velocity stacks” in out air box are mainly there to get a well developed air velocity profile to ensure optimal atomization of fuel. Yamaha engineers may of had a targeted RPM range in mind they wated to hit as well (mid range king comes to mind)..? Hopefully all these engineering classes pay off some day. Looking forward to hear your opinions.

[Jimmyshifts]

Pod question

So how do i know which size pod to get? All I can find on the card is the company name and "MIC". Should I just tke a shot and order the 54mm from Mike's?

[thewiz]

54 mm is the right size ...

Jimmy. I have 'em on my hot rod G.

[mason79]

pods are noisy and hard to tune, for me anyways and not worth the trouble....

[yamahansolo]

i have run mine in the rain on numerous occasions with no problems.
i did have a problem one day after it rained because all the water had ran down the outside pods and soaked it through but it cleared up after about 10 mins of riding.
i think as long as you are moving or your legs are somewhat blocking the water you'll be fine.

i think the noise and the power increas are very bennificial.
my 79 standard has pods and the kerker and has been rejetted and will melt the paint of of my 82 xj11. down low and otherwise.