K&N AIR FILTER

RU-1700

Or an RU1770, which is what I use, its a whopper but supplies enough air and actually creates a bellmouth effect into the bargain, cheers.

Does it fit inside the air box or do you need to remove the box?

What is this "bellmouth effect" of which you speak?

the coanda effect is what you can notice at your ceiling grill in the office and at home.
The flowing air has the tendency to "sick" to the ceiling for a while, then drops.
The same event can be witnessed when you take a spoon out of a cup with fluid, the fluid will not "run"strait down but follows a curve!

I can imagine the cone on a carb intake, will make the gasflow linear and gets rid of turbulence !

Probably "our" airplane mechanics can tell more about this subject !

Found Bernoulli in wiki :

en.wikipedia.org/wiki/Bernoulli%27s_principle

Hey, I didn't know Bernoulli was part Dutch.

Interesting experiment on filters since there are apparently an infinite number of factors that can change things. (like atomospheric conditions.)

And it's nice to know the K&N filter performed best (on a Mazda at least.) Although on the downside, K&N wasn't better by enough to make much difference.

I've heard lots of turbulence in the airflow is necessary to mix the fuel vapors and incoming air. The trick, I guess, is to get the right amount of turbulence without slowing things down too much. ()

Well, guys, here is my two cents regarding the bellmouth.

I think there are many ways to interpret what a bellmouth does, I will try to describe how I view it from a fundamental (euphamism for impractical ;D) point of view.

The bellmouth or velocity stack essentially smooths the transition of essentially still air to the desired velocity profile inside the pipe to which it is attached. In our case this is the interior of the carb and inlet manifold. If the entrance was purely a blunt pipe the flow would be drawn in to the inlet but the very thin boundary layer near the walls of the inlet would "separate" at the sharp edge. Once the BL(boundary layer) separates from the wall the and contracts the orifice diameter effectively decreasing the size of the carb diameter. (very similar to a Vena Contracta -- see wikipedia). Seperation also implies that a bunch of vorticity created in the BL will be dumped into the flow which is the source of turbulence. Now, turbulence isnt necessarilly a bad thing for mixing but in the case of a sharp orifice there will likely be vortical large structures and an unpredictable spped next to the jets etc leading to pulses at the jet entrance etc. The turbulent pipe flow will also be slower -- all the energy creating vorticity results in a slower flow.

The good news is, the bellmouth keeps the boundary layer attached and leads to a smooth velocity profile (shape) in the carb. Now, once the flow goes through surface perturbations in the carb, manifold transitions, turns corners etc...more vorticity will be created, separate from the surface and there is likely occurence of turbulence.

When thinking about this its very important to distinguish the sucking flow through the bellmouth from a jet flow out of a pipe. Think about the difference between blowing out a match (easy at several inches) and sucking out a match (nearly impossible). In the case of the jet, vorticity and turbulence is generated and creates a concentrated jet that stays in tact for a great distance. A sink flow (sucking flow) draws from a sphere essentially and has no concentrated region to it. so, if the entrance to the sink is kept smooth, there will be less tendency for a concetrated region of turbulence ( jet like behaviour) to develop.

Hope this helps.

Bill--

Thanks PC! Try my best.

Realized after reading through the posts that I hadn't addressed the Coanda effect.

I dont think Coanda really applies here. The Coanda effect is a very subtle thing in the field of fluid mechanics and can be very contentious ( I am setting myslef up here I think !!) . I think Dutchcool is referring to the tendency for concentrated jets to stick to convex surfaces. This is exactly what Coanda observed as he lit his plane on fire with a turbojet exhaust of some sort I believe. Basically, a jet will "attach" itself to a surface and follow the contour of the surface instead of staying directed in a straight line. This effect arises because of the interaction on the jet with the surface. The jet will scrub off momentum at the surface. If you look deeply into the governing equations you find that the momentum loss will result in a loss in pressure also -- makes sense, the flow looses some energy. So, there will be a pressure gradient driving the jet towards the surface -- the jet stays attached to the surface.

However, in the SR carb inlet case, the incoming flow is not a jet (see my post above) and enters substantially laminar. An entrance flow such as this can stays attached to severely contracting geometries. There is no Coanda effect here. On an exit flow (downstream of the carb for example), we are limited to just less than about 10 degrees of divergence before the flow will separate from the wall and cause all sorts of trouble. Note that this is different than Coanda since there is no real concentrated highly energetic jet seeking to attach itself to a surface.

Bill--