A Question for Airflow Experts

Something I've always found interesting is velocity stacks: the various shapes and lengths old bikers used back in the day. I've found technical articles on airflow design and high vs low pressure and how engines respond at different RPMs etc. So naturally I began scratching my head when I came across what Mr Yoshi has on their newest carbs (currently in testing phase). Its a dual stack air funnel or simply a floating velocity stack. From their website it looks like they are used mainly on minibikes and 125 pro race bikes.

Can someone with a bit of technical background explain how these would be better than an airbox or normal stack?

Because carb porn?

That's the same idea as some bikes with variable intake lengths. We all remember that intake length from opening to valve head resonates at certain revs and long intakes are better at low revs and shorter ones at high revs.

At low revs, air can be drawn in through both but the wave resonates with the longer stack. AT higher revs it resonates with the short one. There was a guy working on similar ideas for his Ducati twin a couple of years ago. Not sure if I can find that reference. Ah found it. http://www.superduke.net/forum/viewtopic.php?f=1&t=14265&hilit=rc8+stack&start=300

In that case the idea had one stack inside the other to achieve more or less the same effect.

https://www.google.com/search?q=variable+intake+length&ie=utf-8&oe=utf-8 courtesy of Google

This photo bout sums it up. very cool. thanks for the link teazer.

Carb porn for 500 Alex

...having difficulties cleaning up all the drool

Doc, that's an interesting graphic for the side mounted carb with dual intakes to smooth flow. Different application of the same thought process.

And yes, those carbs are pure bike porn. Talk about form follows function.

Thanks for the links teazer, really loving that airflow map comparison. Ok now I want a set of these, Solidworks here I come!

Lots of interesting stuff out there.


Yamaha applied the technology to the R1 a few years back http://www.yamahapart.com/page/yamahaycci

https://www.youtube.com/watch?v=N-oJ9DHg7KU

Even my old Fort Escort GT had a plenum with two passages. at a certain speed it would change from the long one to the shorter one. Same idea of being able to better match the intake tuned length to different RPM bands to stretch the powerband.

https://en.wikipedia.org/wiki/Variable-length_intake_manifold

When we were racing CB160s' we tried different length intakes on the dyno and while the difference was not huge, it did allow us to choose one that best suited what our motor and rider wanted. A decade or so earlier I tried a range of different intake manifolds on a CB72 and while the longest was probably best, it wasn't practical. This is a way to have both. Gotta love that.

Great vid

It's a bit simplistic but it gets the point across. In reality, that wave will reverse itself many times per cycle and inlets are usually based on 2nd or 3rd order waves else they would be way too long