Engine Masters' Air Filter Test

[Tuner]

The total area of the holes in the 'screen' in this sort of velocity stack/filter can be less than the area of the carb venturis. This is like running a restrictor plate above the carb instead of below it. In either case it restricts air flow.

[Cris]

R2C made this filter assembly for me. (They are a great company to deal with.) I have very limited clearance under the hood. The filter is a fine mesh screen that R2C says flows very well. I have never tried it on a dyno. And I do have some concerns about the filtering effectiveness of the screen.

[MadBill]

Tested everyone of those on the flowbench AND the dyno. Some surprising results. The raised 2" center section flowed less than the best which was the standard open by quite a bit. It was a surprise when the 2" raised made the same power as the best flowing insert. The 4 hole was a disaster all the way around in my case. J.Rob

Some years ago I flowed several of the above. The short plastic radius piece gave a small but worthwhile gain, but the 'inverted bowl' type at the top was terrible; with a 3" filter much of the flow was blocked by the almost vertical wall immediately inboard. By contrast, a properly formed drop base patterned after the original L-88/Z-28 part was about as good as decent non-drop open element. A spun aluminum top much like the lid in the lower left assembly was also poor, I believe due to the oversize flat (larger diameter than this one) at the bottom disrupting flow into the venturi.

[MadBill]

(double post)

[BOOT]

The total area of the holes in the 'screen' in this sort of velocity stack/filter can be less than the area of the carb venturis. This is like running a restrictor plate above the carb instead of below it. In either case it restricts air flow.

I thought that as well, as I've read the same about aftermarket oil pick-ups having that problem.

edit: Also for example I noticed long ago the cheap oiled filter at local parts stores would only have half the folds as a K&N or even some paper filters. But from their testing filter surface area seems to not matter much as I thought as long as it's clean.

[Truckedup]

Some bike guys have known for a time that coarse mesh screen or perforated steel over velocity stacks restricts air flow...On the chassis dyno my 40 cubic inch twin push rod hemi with two 34 MM carbs makes about 1.5 HP/CI.... a 3 inch wide by 5 inch long K&N filter on each carb caused a slight power loss...An oiled foam of the same size was worse. Best power was made with no stacks or filters.... I didn't have time to dick around messing with the filters or velocity stacks so maybe tuning might have gotten the power back or found a bit more...

[Mattax]

The total area of the holes in the 'screen' in this sort of velocity stack/filter can be less than the area of the carb venturis. This is like running a restrictor plate above the carb instead of below it. In either case it restricts air flow.

Another issue with a screen, any screen, is that with increasing velocity and pressure they look more like an obstruction.

My theory is that given an adequate size cylindrical filter, adding the X-Stream top produces turbulent intersecting flows that affects metering and distribution. If the normal filter is badly undersized and/or the case poorly designed, the filter top could produce significant gains because there isn't much lateral flow to tangle with. At the opposite extreme, say a 16" x 4" K&N, there may be so little restriction that hardly any air flows through the lid and so it does no harm.

I think the questions about flow interference and turbulence, and the role of the bowl vents could be better understood if we can see the WBO2 AFR - rpm for each of those pulls. For example, with any or all of the downflow arrangements it would not be surprising to see effects of increasing pressure in the bowls. Anyone know if its possible to get the AFR curves?

[Mattax]

I'm sure most of you have this book (Urich & Fisher), but I'll post here for convenience. I only wish they were a little more specific (such as how tall is tall?). But the overall results are pretty much as one would expect.

IMG_6132.JPG

[CharlieB53]

I suspect the 'Tall' Truck air filter element is the 14 X 4

And the aftermarket 14 is the 3 inch tall element