EFI Filter Air Flow Calc?

aldersonjames20 · #1 (**permalink**) 04-11-2007, 07:58 AM

I am still trying to come up with a better looking way to filter my IR setup. I have gone through all the normal ways of doing it and they all fail to work on my setup as there are some quirks with mine. My stacks are canted towards each other at an angle of 12 degrees on each side. This was because the designer opted to mill the intakes down so his injectors pushed fuel almost directly into each intake. He also custom spun the velocity stacks to fit the 56mm throttle bodies so they are wider than any I have seen, especially at the top where they are 4 inches OD. This stops me from using any of the options most would go with such as the screens or the rousch individual snap on K&N's.

So, I have come to the conclusion that I am going to have to have some kind of filtration fabricated for me. My last idea was to take one of the cobra oval air cleaner units and have the base modified to fit the stacks. This seems doable (very tight fit) but I am being told the 1.5 inch filter won't cut it for the amount of air I need. I can't go to a longer filter as I don't have the hood clearance. So.. I think I am just going to plug each velocity stack with a K&N conical air filter and have them sit on the top of each stack. I am hoping I can get an extended flange version so it will litterally fit in there fairly snuggly and won't come out, otherwise I am going to have to come up with some other way of clamping them on each stack.

Ok, after all that explaination that you probably didn't need (just me venting), I need to know if there is a calculation that would tell me what airflow I need to get through any filter I choose. I am looking to calculate this for each stack so I can find both a filter that fits and breathes well enough to put on and not kill horsepower. Its probably an easy thing to do, but I would think it would depend on cam and heads etc correct? Anyway, please let me know if there is one I can plug my engine specs into.

Thanks.

James

Power Surge · #2 (**permalink**) 04-11-2007, 08:22 AM

James, Outerwears can make you slip on prefilters to fit right on your stacks. They custom make them to any size you want. I had some made for my brothers Harley to go over the open air horn he was running on his carb since he wasn't running a filter. You can get them in any color as well.

Cobrabill · #3 (**permalink**) 04-11-2007, 08:31 AM

Those stacks can be shortened with no detrimental effect,ya know.

aldersonjames20 · #4 (**permalink**) 04-11-2007, 08:42 AM

Quote:

Originally Posted by Cobrabill

Those stacks can be shortened with no detrimental effect,ya know.

I realize they don't need to be this big, the problem is that things like the fuel regulator is in the way of lowering them on the backside. Its also not an easy or cheap job since they would need to be setup for a machine and they are flanged etc... didn't seem worth it unless it stops me from filtering. If i can't find anything else to work, I will shorten and possibly straighten them and filter them that way.

James

Cobrabill · #5 (**permalink**) 04-11-2007, 08:58 AM

Hmm,the interference issues are not visible in the pic.I was considering a similiar set-up years ago but $hitcanned it for a couple of reasons,one being the PITA airfilter situation.Good luck with it,it does look B.itchin'!

aldersonjames20 · #6 (**permalink**) 04-11-2007, 09:51 AM

Quote:

Originally Posted by Power Surge

James, Outerwears can make you slip on prefilters to fit right on your stacks. They custom make them to any size you want. I had some made for my brothers Harley to go over the open air horn he was running on his carb since he wasn't running a filter. You can get them in any color as well.

Don't those pre-filters just keep out the boulders? I am looking to truely filter the air as well as possible. I suppose I could just change the oil every 1K miles or so...

So nobody knows a way to calculate what the cfm requirements are for a particular engine? How bout a cfm that is guaranteed to give me a good breathing filter? If I was to have a carb on here, I am guessing it would be somewhere between 800 and 850 cfm... so does that mean I can take that number and calculate around it?

James

Power Surge · #7 (**permalink**) 04-11-2007, 11:44 AM

Quote:

Originally Posted by aldersonjames20

Don't those pre-filters just keep out the boulders? I am looking to truely filter the air as well as possible. I suppose I could just change the oil every 1K miles or so...

So nobody knows a way to calculate what the cfm requirements are for a particular engine? How bout a cfm that is guaranteed to give me a good breathing filter? If I was to have a carb on here, I am guessing it would be somewhere between 800 and 850 cfm... so does that mean I can take that number and calculate around it?

James

Outerwears material is very fine and will filter very fine particles. Many race cars use them as their only filter, as the material does not impede airflow, yet filters good.

Cobrabill · #8 (**permalink**) 04-11-2007, 12:38 PM

I can't comment on what PS posted but the "socks" that were designed for Webbers do in fact, just keep the boulders out.

Tom Wells · #9 (**permalink**) 04-11-2007, 12:49 PM

Here's K&N's calculator for air filter size (square inches):

http://www.knfilters.com/filter_facts.htm#SELECT

I've often wondered whether folks who worry about manifolds, ports, induction systems etc. sometimes consider a small hood scoop more important than air flow through a filter. Ditto on the power loss experienced between the engine dyno and the chassis dyno.

My car has a bit of an oversized scoop to allow enough filter area. Chassis dyno results are all I have, so no real comparison is available - probably I do have enough air filter since I did follow K&N's guidance.

Hope this helps,

Tom

jetenginedoctor · #10 (**permalink**) 09-06-2007, 09:31 PM

Although it doesn't "look" as cool as individual filter elements for each inlet horn, a larger single element will provide far better performance benefits. Consider the fact that no two cylinders are filling at the same rate at the same time. Allowing cylinders to breath through a larger filter element that serves multiple cylinders means that the resulting depression across the filter is smaller and has of a "secondary throttle plate" effect on the engine. We've removed pod style air filter elements on several engines and replaced them with an airbox equipped with a panel filter element or circular/oval element and have seen dramatic improvements in top end horsepower, not to mention the fact that the throttle bodies are a lot easier to sync that way.

Your milage may vary. . . . but I doubt it.

Brian Kennedy