pressure drop across air filter

Ok, I must be missing something basic here....

Why not just use a run of the mill cheapie dial vacuum gauge from a cheap tune up kit and measure it like 'ported' vacuum?????

At idle it is going to be really low, open it up and you get 'manifold' vacuum. Change the shape of the air filter and the ported will change radically. The manifold vacuum is the one I would be watching....

Or if you are really serious about playing around, just drill a hole and tap a nipple into each manifold so you get the manifold vacuum at all times?

Other than that, the vacuum cleaner will give you an idea of the differences, but in real life, well....

I keep track of my gas mileage and when it starts to climb, I start checking things like filters......

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Matt wrote:

Not sensitive enough. 15 PSI is roughly equivalent to a 30ft/360" of water.

If you want to make really accurate measurements, you have to be sure that you are measuring the parameter you really want to evaluate, at the exact and reproducible conditions that you would use across the range of filters, and that your measurement method is accurate.

Temperature, air density, atmospheric pressure, humidity, air velocity, etc might all be important. If you want to measure the restriction imposed by the filter, these parameters, in the same range as what you would experience on the road, might be all you need.

If you want to measure the efficiency of the filter to remove particles of different sizes, other tests would have to be carefully devised. Ability of the filter to continue to function as the particles accumulate may be important.

This is why it is hard to give a definite answer when asked 'Is K&N the best filter out there?'

The more you try to get a test that gets usable data, normally the more difficult it is to obtain the data, and the more expensive and complicated it becomes.

I was thinking the same thing about an orifice plate. Not sure whether the filter DP data are meaningful unless the air flow rate is known and/or known to be comparable to air flow rates at top speed.

Atmospheric pressure is 760 mmHg. The density of mercury is 13.6 times that of water.

0.760m * (39.37 in/m) * 13.6 = 407 in = 33.9 ft.

While you're up to your ass in technical jargon like static pressure and differential pressure and universal gas constant, absolute pressure, gauge pressure, temperature in degrees Rankine, Newtonian physics, Bernoulli, Kutta-Jukowski, Coanda effect, standard atmosphere, Boyle's Law, Charles Law, Gay-Lussac's Law and associated formulae, don't lose sight of your original intent, which was to correct the relentless carbon fouling problem in your CJ-360...

Have you tried riding with the one new filter installed and checking the spark plug, or what? Please do that test, before I succumb to senile dementia...

I won't be likely to contradict you on that---it seems to make sense to me.

My bowls are vented to atomsphere. In each bowl there is a little "standpipe" that is open to the headspace and passes through the fuel and down through the bottom of the bowl. The bottom end of that pipe is equipped with a foot-long rubber hose that extends approximately to the bottom of the frame. When the bike is moving, the open ends of the hoses have wind blowing past them. I've been running without the hoses lately because they tend to get in the way when I am doing carb work. I don't expect that running without the hoses matters much.

If a given filter acts virtually like an orifice plate, then the flow rate is proportional to the square root of the differential pressure.

Then for either of the used filters, the flow rate increased by a factor of sqrt(58/40) = 1.2 in Experiment 2 (E2) compared to Experiment 1 (E1). So flow increased by 2/10.

For the new filter, the flow rate increased by a factor of sqrt(44/19) =

1.5 in E2 vs. E1. Flow increased by 5/10.

Thus the new filter was able to accomodate an increased load better than either of the used filters.

Sorry to make us all wait ...

Here is a rough estimate of the air demands of an engine cylinder.

If a two-cylinder bike consumes a gallon of gas in thirty miles at

90mph, each cylinder is using a gallon in sixty miles, or 60miles/90mph = 2/3 hours = 2400 seconds. A gallon of gas weighs about 5 1/3 lb, so if the fuel mixture ratio is 14, its burning requires about 75 lb of air. So air is needed at a rate of about 75 lb(453g/lb)/2400 sec = 14 grams/sec. The density of air being about 1/780 that of water, the cylinder uses about 14g/sec * (0.780 liter/g) = 11 liters/sec = 11 l/sec (0.0353 cu. ft/l) = 0.39 cubic feet/sec.

Thus an air filter needs to pass a cubic foot of air in about 2.5 seconds.

Now to measure the flow rate of my shop-vac ...