What size of air filter is needed for modified trucks? I know it depends upon what type of mods. Is there a formula that shows how many square inches are needed to supply the needed air for given horsepower?
K&N has a formula on their site, but it doens't take into account a supercharger.
The filter I was using had 230 something square inches. I am currently using a filter with about 170 square inches. It almost feels as if the truck is down on power with that filter. I was thinking about going up to a bigger size filter maybe 250 square inches.


Just got off the phone from K&N. They also faxed me some formulas.
FORMULAS
1. Square inches of filter required for a motor.
(CID X Maximum RPM)/20839
2. CFM required for most motors
(CID X Maximum RPM)/3456
3. CFM required for a supercharged motor
[(Pounds of boost/14.7) + 1]
this relates to #2 example
(CID X Maximum RPM X #3)/3456
CFM Formulas for filters
round
diameter X height X 6 X 3.14
flat panel
length X width X 6
universal round taper
(base + top)/2 = A
take A X length X 6 X 3.14
universal round straight
diameter X length X 6 X 3.14

(cubic centimeters/16.39=square inches)

I have approximately a 331 CID and have up to 26 psi boost.
[(331 X 5500 X 2.77)/3456] = 1458 cfm
The filter I was looking at was a RF-1026(cone filter with a 7.5 inch base and a 7" top.)
(7.5+7)/2 = 7.25 inches
7.25 X 11 X 6 X 3.14 = 1502 cfm.
It looks like that filter is going to be big enough for the amount of air.

 

An easy way to modify this for a SC is to simply do:

(boost+15)/15*CID

so a 4lb pulley (12 lbs of boost)=171 inches

A KB running 26lbs of boost = 259 inches

I used 6000 as max RPM...

Coldie

 

how do the filters that come with the PSP fast air kit stand in this?

 

It has been mentioned in the past that some people get away with running smaller filters. Why is that?

 

Serious question: You have a Airfilter than can flow 1500cfm but your Throttlebody only flows 1000CFM

 

You are right. I measured the BAbolt TB I have awhile back and I think it was around 10.5 square inches in area. That didn't take into account the throttle plate...I never had it flow tested.

 

Any other thoughts?
Since my throttle body has around 10.5 square inches of area and if the supercharger is trying to pull all kinds of air through it at boost, what could be the max air flow through it?

 

I emailed accufab and they said, "The Lightning TB is bigger than 90MM and flows 1697 CFM naturally aspirated."
So since the max cfm I need with 26 psi is only 1458 I guess I'm okay.

 

I dont know what BaBolt TB flows but I think if you go to accufab site it lists the SVO and Accufab flow numbers. We really are making a big deal about nothing, if Im not mistaken the Accufab Oval flows more than a Accufab 90mm Round. Yet the round is on over 90% of the EFI Super Street Outlaw and Pro 50 cars out there.

 

I don't understand. You said, "Serious question: You have a Airfilter than can flow 1500cfm but your Throttlebody only flows 1000CFM." Where did you come up with that number? Now you are agreeing with accufab that there TB flows over 1600 naturally aspirated? My BaBolt TB is bigger than the accufab they were selling back in early 2002. I measured the two.
I don't think this is a "big deal about nothing". I would like to know what size air filter I should use. Is it an airfilter with 100, 200, 300 square inches of area?

 

Easter I sent you a email, I dont know the proper answer to your question. Here are my thoughts on the subject, its better to have the filter be able to flow more than the TB or Engine, than to not have enough air be able to move through the filter. If your filter is so small your going to colapse the filter and possible damge could occur. I would also guess that the less of a restriction you have before the blower, the less stress it might put on the blower(Making it more effiecent). Here is another thing that just came to my mind, I use to have a 4.6 Liter Mustang with Novi2000 pushing 25lbs Boost. The air filter that came mounted to the Mass air meter was very small, yet the car was able to make massive power. The Novi 2000 can move way more air than a Eaton, if Im not mistaken it moves of 1200CFM. I am just as confused about this as you, please let us know what you might find.

 

I don't know the answers to this.
I do know that the truck feels slowers when accelerating hard with the 9" 190square inch filter. I stick on the bigger filter and it feels better. I have switched the two a few times. I have never done it at the track or on the dyno.
I don't plan on spending money to have the intake flow tested.
I cut the babolt power pipe a little shorter and stuck on a 6" adapter hat. I plan on using that with a an RF-1026 K&N filter which is 11 inches long, 7.5 inches wide at the base and 7 inches wide at the top. That should flow appoximately 1502 cfm.