Velocity stacks with filters for VM29 smoothbores

Here's some pictures of a project I've been working on. I run VM29 smoothbore carbs and have been using them in combination with K&N pod filters. I'd been wanting to experiment with adding some intake runner length to boost flow/midrange. The most effective way to do that is with open velocity stacks, but with a bunch of dirt and dust getting sucked into the motor this is hardly practical on a road bike, unless you want to rebuild your top end every year.

So I'd been kicking around the idea of making velocity stacks and stuffing them inside an oversize air filter. I even bought a few feet of aluminum tubing and some dual flange GSXR filters about a year ago. Of course I
parked it under my desk and that's where it all stayed until two months ago, when I finally turned a prototype on the lathe. Now I'm no machinist, it took me damn near an evening to do one and it was far from perfect. The thought of making 3 more (and have them be remotely
similar) was discouraging to say the least. Here's the prototype stack:

Luckily, I got talking to Wompy who was already doing some cool stacks for KZ650s. He turns out to be a badass machinist/fabricator and a stone's throw away. He was down to do some prototyping so I sent my stuff down to him and a few weeks later I got these bad boys in...

I've tried two different lengths of stacks and the shorter ones seem to be working better (probably because of room inside the filter), so we're gonna develop these a little bit more. Mid range gets a nice little kick with the stacks and as an added bonus this set up is much less sensitive to side drafts at cruising speeds!

As you can see it's real tight on the frame and it's a bit of a squeeze to get the filters on the carb throats. The filters got dented a bit after a while - I was working on my jetting as well so they went on and off at least twenty times, which didn't help.
The final stacks will be made out of delrin - this will clamp down better and be a bit more flexible when mounting. Also the filters will scoot over about 1/4" towards the carbs to gain a bit of clearance.

For those with keen eyes, these prototype stacks were smooth on the inside because my carb throats have been blended to a paper thin edge. The delrin ones will have an accurate step on the inside to create a smooth throat with uninterrupted flow from the bellmouth inwards.

Holly crap.... SWEETNESS!!!!!

One thing I dislike about the Keihin CR's is the small lip area to secure a POD...

Even if just a small extension to the carb body where gives the POD a better bite....

Damn good idea there Dutch....

OMR

Yeah the VMs have a 10mm flange so plenty of room for clamping. On the bright side the way the CR's mount you get a bit of intake runner length with the screw on flange between the carb and the motor.

I was also thinking abou8t notching the banding strap...
Just under the top side area where the clamp won't ride under.... Notch ~ 1/16th - 1/8th around it would be perfect/non slip...

Ah well, they haven't fallen off so who knows....

Wonder if I could sell them on e-bay.... :laugh:

so when are you making me a set?

Well we're making a few small tweaks and the design should be ready to go. I bet Wompy can make you a set!

Here's another view installed on the bike from an angle. I'm pretty stoked on this setup. The stacks stick into the filters a good click but they are far enough away from the back wall to not impede flow. I like the way these big ole filters look on the bike.

This is what it looks like straight down the throat... You can clearly see my carbs have been modified from stock by removing all the blind ports and blending the edges.

Last picture (for now) is a close up of the stacks in the filters. These were the longer ones I think.
I am trying to get the bike on a dyno for some back to back testing!