Pod size question for drag ported cub

[mike0chek]

hey guys i recently ripped one of my 6 inch pods so bought some 8 inch ones to replace them. has anyone ever done this upgrade and ave to rejet because of the larger filter?

 

heres my mods. 421 drag ported cub, 35mm carbs, inframe shearers, +4 timing, vforce 4's, fast clutch, 4mil hot rods

 

pretty sure it has 160 mains with 30 pilots at about sea level.

 

any input is appreciated

[Nightmare]

I really think it will make a difference, could be wrong

 

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[mike0chek]

i was thinkin the same, never seen this subject come up on hq before

[sheerider11]

I had this discussion with my father a few months ago. I had little stubby UNI filters to put on my girls bike. He told me those things are a joke, so we kept going back and forth about it. We never tested anything, but figured that they'll only fail if you can pull enough air to collapse them. I don't think her bike would pull that much air to out flow the filters. There open 360 degrees around. It'll take some vaccum to out flow them, I think more then some bikes make.

But for all I know we are both wrong and way off course. Like I said it was a discussion that we had and just left alone. Her bike runs fine btw

[Bennett131]

I went from 5 inch uni foam filters to 6 inch ones and I did not have to change my jetting they are all different tho

[J-Madd]

I would think the flow for a Cub is maxed out with the 6" filters (especially with 35 mm carbs), so anything bigger shouldn't make a difference. Do a WOT plug check to be sure it you're worried about it.

[mike0chek]

yes ill def be plug chopping. jeff at fast told me he would def run an 8 inch over a six inch pod anyday for any drag ported cub so when my 6 inch ripped i upped the size.

[m671054]

Found some formula for figuring required surface area needed based on engine size and peak hp rpm. any idea what a as cast cubs volumetric efficincy is?

[J-Madd]

At 100% volumetric efficiency at 10,000 rpms I come up with 37 cfm per cylinder,  I don't know if the motor is more or less the 100% VE though. I also just used google to find these calculations, and I don't pretend to know this.