Air Filter Calculator

[750hp]

David, it would have been interesting to have then compared a drop base filter assembly or a 2" filter, because the problem is usually that you can't fit a 14x3 in a Cobra like you can in a tintop.

[mikeinatlanta]

The K&N calculator shows I need a 14X3.7. When building the intake using the actual media flow numbers it came out to 14x4.1 so not too far off, but still a little happy. I'm running a 14x5 for just a bit of margin.

[DAVID GAGNARD]

Originally Posted by 750hp

David, it would have been interesting to have then compared a drop base filter assembly or a 2" filter, because the problem is usually that you can't fit a 14x3 in a Cobra like you can in a tintop.

This engine went into my 1965 Mustang Coupe road racer,same one in my avatar.......

The air filter housing actually was a drop based filter...on the Mustang,you can run a 2" filter and it will fit under the stock hood,barely.......I wanted at least a 3" filter,so I had got a drop base filter housing of 1.5"s and that is what was used on the dyno and the car.....

David

[Dwight]

three years ago I was working on a B&B with a stock-ist 351W. We took it to the industrial park and ran it thru the gears. It would not rev pass 4300 rpms in any gear.
We pulled over to the side of the road and looked under the hood. It had a 8" S&H filter . We removed the air cleaner/filter. Now it would pull to 6,000 with no problem.
The air filter was clean.

We bought a larger filter and problem solved.

Dwight
I put the 8" filter on my old 79 Ford truck with a 302. It could not rev to 4000 before the filter, so the filter can hurt it. LOOK good on motor.

[itstock]

Back to back dyno pulls, using the tiny K&N filter on my 351w 427, it went from 461rwhp with the filter to 482rwhp at 5600 with no filter.

[trularin]

I did my own calculations.

(( CID x Max RPM ) / 3456 ) * 1.1 = CFM...I use this for the cubic feet.

Then the square area of the filter AND the filter level.

If your filter is very fine, like 5 microns, you are going to need a larger area to allow the same amount of air to flow through.

Then there is the accumulated time to a reduction in flow. If you use an area that equals your calculation, you are going to be at a loss as soon as you pull in air and filter it.

Not sure if this hellps anyone, but it is interesting when you are thinking of putting in cold air intake system.

[mikeinatlanta]

Originally Posted by trularin

I did my own calculations.

(( CID x Max RPM ) / 3456 ) * 1.1 = CFM...I use this for the cubic feet.

Then the square area of the filter AND the filter level.

If your filter is very fine, like 5 microns, you are going to need a larger area to allow the same amount of air to flow through.

Then there is the accumulated time to a reduction in flow. If you use an area that equals your calculation, you are going to be at a loss as soon as you pull in air and filter it.

Not sure if this hellps anyone, but it is interesting when you are thinking of putting in cold air intake system.

I think level of filtration and filter area is where the calculators have issues. One 14X4 may have double the effective filter area when compared to another one of the same size. If you don't know the media flow characteristics new vs. after some use, the calculators are only valuable for new filters.

All of this is why I am of the belief that most cobra owners are losing much more to filtration than they would like to believe. I would love to have gone with a 14X4 but the math clearly supported the need for 14X5 for a 700 hp engine.