I know that too small can hurt, but can too big be bad?

And how do you know what size filter is too small without measuring kPA?

I'm putting together a cold air intake, and I want to make sure I get a filter that won't hurt performance any time soon.

 

No such thing as to big. As for to small you either rely on the manufacture in stock or near stock configs. Or for anything unusual, most filters have max CFM for the filter on the box or in the advertizing, so all you need is your engines max CFM.

 

with a stock computer it can hurt if you have to much intake, it will almost act as if there is a caccum leak, and the check engine light may come on because of extreme lean conditions.

 

You don't really believe that, do you? Its totally incorrect.

 

I have run stock vehicles at the track with no air filter with no problems.

I guess I asked the wrong question.

I'm wanting to know how you figure out what the minumum size air filter you should run.

 

ive done it, it needs some restriction or the car will not continue running. Try running the motor with an open intake and see how far it gets you... now would you like to chime in on some contructive comments?

 

let me guess, you tried running an LT1 without the MAF?

My best ET was with no air filter, 85mm MAF, rubber boot to throttle body.

 

Im sorry, im wrong. The more I think about it the more I see how misunderstood I was.

 

If the MAF is plugged in but not connected to the TB then the car will not run. If the MAF is unplugged it will run, be slightly harder to start but still run pretty well actually.

Cheston if you look back through the SS forum archives some kid "etnies" or something like that had a massive diesel filter on his car, might be a source of inspiration. Think the exact one he had was a tad overkill, not that that hurt, but still might be worth a look.

Want to say the think was 16" long at least and 6-8" round paper.

I have thought about making a box for the RAISS to allow a LARGE flat paper element rather than the cones. I have one cone now that is restrictive and the other has too deep of a cone in the end that gets too close to the MAF and readings get inconsistent because I tried to descreen it to measure the running difference and ruined the screen.

 

On my 381ci LT1 (set up to run speed-density, so MAF is not an issue) removing the air filter has no negative effect whatsoever - in fact, it increases engine power. I've run it on an engine dyno with and without the induction system, and it makes more power without all the plumbing and the filter. A velocity stack on the throttle body, with the correct radius on the outer edge will improve HP, but that's because it smoothes air flow and reduces the vena contracta compared to the blunt, irregular shape of the throttle body housing.

Your intake does not need "some restriction" any more than your exhaust needs "backpressure". Some fundamental reading on building performance engines might be a good idea. Look at the David Vizard books.... he deals with basic issues and supports his positions with real-world test data. Here's a good one:

http://www.amazon.com/exec/obidos/AS...0target=_blank

 

Of course I can't find it now, but there are formulas for calulating the max CFM based on engine size, head and intake flow rates, etc. I'm sure "Desk Top Dyno" and the like, have this in them.
Once you have this rate, most go with a slightly larger filter. For instance, say your engine pulls a max of 728cfm at 6000rpm. You would be good with a filter/air duct good for 750cfm. or larger.

 

If DesktopDyno or DynoSim have that calculator, then I haven't found it.

 

350ci times (rpm divided by twobecause it is a 4 stroke) = then divide by 1728 the number of cubic inches in a cubic foot
This assumes 100% VE for ease of math, multiply the results by whatever VE you deem fit.
For 6000rpms that means 607cfm the thing you have to consider is what depression was the filter rated at???? If rated at a high depression a "750cfm" filter will be a restriction.
If a filter is rated at say 1" of mercury which would be a good number for manifold vacuum at WOT and it flows 750cfm then it should be of no meaningful restriction.