Air filter size

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jhenn4716
Posts: 50
Joined: October 11th, 2010, 9:11 am

Air filter size

Post by jhenn4716 »

I've seen different sized/shaped K&N filters. Is there a performance difference between the different sizes and shapes? I know that different filters can fit in different places, outside of that, is there any difference?
Jeff
Mysterian #55
FV80
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Re: Air filter size

Post by FV80 »

Jeff,
I haven't tried a LOT of different sizes, but if you keep them cleaned, there is "very little" difference between the various sizes. I use a 6" tall version and have been beaten on a couple of occasions by someone using one of the 3" tall versions. If you have a 'tight fit' situation, I wouldn't worry about the physical size - although you DO need to keep an eye on it. Obviously, lesser sq inch area will tend to clog more quickly.

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
SR Racing
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Joined: June 24th, 2006, 1:58 pm

Re: Air filter size

Post by SR Racing »

The flow requrements of an FV engine are much lower than most any K&N filter that fits the carb. Any of them is fine. Actually on the flow bench a 28pci carb flows slightly better with a filter on it. WIth no filter the carb inlet is filled by the air mass that enters the throat. When you install a filter the air mass that "misses" the throat forms a high pressure area at the base of the filter, outside the throat. This high pressure area helps to feed the throat. It is the same principle that is used on many big bore engines where a flat plate is installed at the carb top. It is typically in the 1 to 2 CFM area on a Vee.
Rolling Stone
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Joined: January 13th, 2011, 7:54 pm

Re: Air filter size

Post by Rolling Stone »

My Girlfriend(CREW) said size does matter... :mrgreen:
kkapelke4
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Joined: June 1st, 2011, 11:40 pm

Re: Air filter size

Post by kkapelke4 »

frank why is she with you??????
MCRacer
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Joined: June 28th, 2006, 12:14 am

Re: Air filter size

Post by MCRacer »

In the same vein, how about the air flow to the filter? Does it have to sit out in "clean" air or can it live in a blocked area - say behind your helmet?

Mike
SR Racing
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Re: Air filter size

Post by SR Racing »

I am not sure you can achieve any real boost to your intake without an offsetting aerodynamic drag on a Vee. You could put a tuba on the car as an intake and get some real boost. Maybe as much as 4 or 5 HP. But the drag would offset the gain. The secret is to have the intake where the highest pressure air already exists and is wasted. As an example NASCAR etc. picks up their intake at the rear of the hood where the windscreen creates an existing high pressure area.
More important and functional in a Vee is getting the coolest air you can get to it.

I built some circuitry with a pressure transducer for Scott (Diamond Formula Car) for his AIM system. Maybe he will share his results of testing. :lol:
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Air filter size

Post by brian »

Don't know what this means but I've seen cars with some ram air need a larger main jet according to the on board A/F meter. I too have seen improvement in air flow when using a good air cleaner. K&N says their patented fiber construction "organizes" the air.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
smsazzy
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Re: Air filter size

Post by smsazzy »

Maybe they can upgrade the "organizing" of the air to "sorting" of the air. I only want O2 to enter my carb.
Stephen Saslow
FV 09 NWR
SR Racing
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Re: Air filter size

Post by SR Racing »

smsazzy wrote:Maybe they can upgrade the "organizing" of the air to "sorting" of the air. I only want O2 to enter my carb.
Excellent idea. Then you could use the remaining stuff (Nitrogen) to fill your tires. :lol:
Dietmar
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Re: Air filter size

Post by Dietmar »

Many years ago ( too many to remember) there was an article written about FUEL STAND OFF- especially referencing the 28pci, the 28pict and the 30pict-1 VW carbs (that alone should tell you how long ago the article was written).
There was a formula for the HEIGHT of the air cleaner in addition to the actual size.

Have not been able to find the article, and don't know how applicable it would be as I have never experienced fuel stand off, but I do tell my customers to stay away from the flat air cleaners ( some made by K&N) that have a flat chrome top and a fitting for the breather. These seem to work fine in a stock VW however.

For what it is worth- hope it helps

Dietmar
http://www.quixoteracing.com
sabre1
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Re: Air filter size

Post by sabre1 »

Dietmar is correct. A few years back, I was dynoing an engine that had the low profile K&N air cleaner and switched to the more typical tall version and saw an immediate and noticeable HP improvement. Flow testing prior to the dyno session alerted me to the fact that the low profile filter might be a problem. The low profile filter was used because it would fit under the engine cover - that car now has a hole in the engine cover and a tall K&N fitted.

-Jim
VDF1
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Re: Air filter size

Post by VDF1 »

I think it may all depend on the "low profile" air filter. When I bought my car many years ago it had the low profile K&N installed and a respected West Coast FV person suggested I might be restricting my air flow, but I couldn't believe the man I bought the car from would have missed something so obvious. I measured and calculated the total "free area" of the K&N low profile and a tall air filter and they were within a fraction of a square inch of each other. The "low profile" had a larger number of pleats and each pleat was deeper. I used the "low profile" when it was hot and the tall one when it was cool.
Life atrophies if it gets too far from risk
brian
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Re: Air filter size

Post by brian »

Standoff is fuel spraying upwards out of the carb. It is a function of rpm, cam design and timing and actually a reversion of flow caused by the pulsing action of the intake charge. If the air filter is low enough, regardless of total induction area it will interfere with the standoff and disturb the charge. Back in the day, two stroke go karts were very sensitive to standoff and a driver could observe these mist columns on the kart in front. Velocity can aid in the management of standoff and were used extensively in karting.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
tiagosantos
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Re: Air filter size

Post by tiagosantos »

I read somewhere last night that in some old can-am cars, you could see the "cloud" of gas over the intake even at full tilt down a straightaway :D I'd love to see that!
VDF1
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Re: Air filter size

Post by VDF1 »

I saw no difference in performance on the track is all I can say. Of course, I was sometimes inconsistent and that may have skewed my results. I don't know how many low-profile filters K&N make. It does occur to me that any filter will intefere with an air/fuel charge above the carb so it's a matter of how much interference that can be tolerated, I guess.

BTW, the "respected FV person" was a driver I raced with 30+ years ago when velocity stacks with no filter were in common use and who quit racing 15 or so years ago.
Life atrophies if it gets too far from risk
SR Racing
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Re: Air filter size

Post by SR Racing »

VDF1 wrote:It does occur to me that any filter will intefere with an air/fuel charge above the carb .
True in respect to the gauss filtering. However the filter design internally and base plate especially, usually HELP the flow.

I just stuck a Regional carb on the bench. I tested max flow with the following K&N's

RU-520 Flow about 105.5
RU-510 Flow about 105.5
RC-1200 Flow about 105.5
RU-570 Flow about 105.3 to 105.4. (This is the very low profile one with the offset carb hole that was mentioned here. )

The dimensions and shapes of these filters can be seen here.

http://sracing.com/Store/FV_Stuff/FV_Stuff.htm

With the possible exception of the RU-570 there was no statistical difference in flow. Before I would even swear the RU-570 was down, I would want to do more testing. It it is that close.

The carb upper bowl shape is 80% of the difference between prepped carbs. When choosing an induction system on a vee getting the coolest air to it with the best possible "free" air "boost" is the primary concern. Any good filter will work fine.
We suck air through a tiny venturi and a long garden hose. That is where the pumping losses are. :lol:
Mystique Racing
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Re: Air filter size

Post by Mystique Racing »

I saw no difference in performance on the track is all I can say.
The differences are small. Your not going to feel it on the track.

However, you might be able to measure a difference on the track if you are using a data system.

Additionally, in this case I don't think the flow bench results tell the whole story.

Scott

Diamond Formula Cars
Scott

Diamond Formula Cars

http://www.diamondformulacars.com
SR Racing
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Re: Air filter size

Post by SR Racing »

[quote="Mystique RacingHowever, you might be able to measure a difference on the track if you are using a data system.

Additionally, in this case I don't think the flow bench results tell the whole story.

[/quote]

Other than potential boost and air temps, I don't see why the flow bench doesn't tell the full story on flow. :lol:

But I certainly agree re: data acquisition on the track for measuring any differences in engine performance. You can look at the rate of acceleration from 70 to 90 (the ET in millsecs) etc. Exactly how long it take to move 1000 feet etc. You can even compute your rear wheel HP directly. And a system to measure all that and much more is under $1000. A tach and all your guages, warning lights etc. and wiring kludge and time to install costs almost as much $.
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