Clear Barrel Throttle Designs Versus The Traditional Butterfly Design

[V-Na]

A few of my co-workers have been talking about throttle designs other than the traditional butterfly design. They claim that there is a flow rate gain to be had by using a throttle which has a clear barrel at WOT. Some designs which satisfy this criterion are the slide throttle and rolling barrel throttle (with either one or two rollers).

A slide throttle would be the easiest to manufacture but may suffer from the dreaded stuck open under vacuum problem and requires a complex linkage to achieve "linear throttle response" due to the fact that it approximates a variable diameter orifice rather than a variable diameter duct. However, a rolling barrel design would be more difficult to manufacture but suffers neither of the two mentioned problems of slide throttle designs.

My initial opinion was that while clear barrel designs would offer a gain in flow rate over a butterfly design of the same diameter, one only needs to slightly increase the diameter of the butterfly design to match this gain. Then any excess in throttle position (with an oversized throttle) could be ironed out with a changing radius throttle cam/[cable guide]. I don't think it would be too hard to adjust the TPS either.

Please discuss, fluid mechanics gurus welcome.

[oldcorollas]

butterfly and barrel are not linear opening designs either...
and as you say, a small increase in butterfly diameter results in same total flow anyway. but it would not be "oversize" because you are only matching the flow...

flow will not be laminar in any of the cases, so it is a moot point, but there will be a difference in turbulence and tumbling of the flow.. but injectors add to that when squirting fuel in anyway so....

think of the flow path of the air with a barrel throttle at part throttle as well...

in the end, it doesn't matter that much

edit: when you are only running injectors outside the trumpets and squirting in, there will be differences at part throttle of course...
but with some bikes, the fuel spray is aimed AT the throttle blade, to improve atomisation in low airflow situation... so butterfly may be advantageous.

[PlacentaJuan]

sounds like something you would do only after you have spent all your money on every other avenue of performance enhancement, and you are chasing that 2 extra kw or so.

[oldeskewltoy]

Hmmmmmmm wonder if you could convert SU carbs to a slide type. In all the years I had SU carbs I never had any problem with one sticking

[Billzilla]

There's a thing called a spike throttle (I think) that has the end of the inlet looking just like the end of a musical trumpet. The throttle is a spike-like gadget (looks like the wah--wah thing that goes in the end of the music trumpet as well) that moves in & out to vary the airflow. I can't find a photo of it nor the copy I have some where on this computer sorry.
But as has been said quite accurately, all you have to do is make the very common butterfly throttle a little larger and it'll flow as much air as any other type of throttle. Yes there's a touch more turbulence, but if you think it'll be a problem then you can machine the butterfly and shaft out of one piece of metal and make the butterfly as thin as you like, so there's no shaft in the way. You have to make a two-piece housing though, but that's not very difficult.

[senn]

What you just described sounds almost like a fuel injector setup, but obviously more controlled than just on/off....or have i misunderstood what you explained?

[horse]

Bill, you're thinking of a Trumpet Mute

[oldcorollas]

Oxford Brookes had the "spike" throttle (when did they start?)
Carnegie Mellon had the "Cone" throttle before that (2003)

[Secks]

okie dokie...
If ya wanna chase that extra couple of Hp, or want something trick, try a set of Keihin FCR carbs. Flatslide, 4 of, with trumpets.
http://www.keihin-us.com/fcr.htm
http://www.aeu86.org/viewtopic/ae86/p/108242
http://www.club4ag.com/faq_and_tech_...tors_4A-GE.htm
Credits to the sites i have linked too.

If it can be done to a 4a-ge, it can be done to anything.
like 8 on a 1uz. crossed supercar style...

[The Real Roadrunner]

you would spend more on the new carbs than it would cost to design and fab a barrel style inlet or flatslide.

Try the OKO carbs, they would be heaps cheaper.

cheers
linden