Airflow requirements

[shadow88]

This should help you select the correct air filter for your engine. I'm pretty sure the wrong one is on mine right now.

To calculate your airflow needs of your boosted engine you take your boost pressure and divide it by 14.7, then add 1, then multiply that number by the cubic inches, then multiply be the maximum RPM your engine will see, then divide that number by 3456 and you get the airflow needs in CFM or cubic feet per minute.

or (boost / 14.7 +1) x cubic inches x maximum rpms / 3456 = cfm requirements of your engine.

This formula is directly from a representative at K&N I spoke with earlier today.

Mine came up at 25 psi and 6500 rpms of 686 cfm. It was suggested by K&N to use an 800 cfm filter for my application.

I don't know the flow of my current air filter, but I know the car feels alot faster without it. Just an FYI

[Reeves]

This should help you select the correct air filter for your engine. I'm pretty sure the wrong one is on mine right now.

To calculate your airflow needs of your boosted engine you take your boost pressure and divide it by 14.7, then add 1, then multiply that number by the cubic inches, then multiply be the maximum RPM your engine will see, then divide that number by 3456 and you get the airflow needs in CFM or cubic feet per minute.

or (boost / 14.7 +1) x cubic inches x maximum rpms / 3456 = cfm requirements of your engine.

This formula is directly from a representative at K&N I spoke with earlier today.

Mine came up at 25 psi and 6500 rpms of 686 cfm. It was suggested by K&N to use an 800 cfm filter for my application.

I don't know the flow of my current air filter, but I know the car feels alot faster without it. Just an FYI

I came up with 1020 for mine. Whoa...last time I calculated (years ago) it wasn't using this method and I came up with 900 something. I'm running way too small of a filter....but I don't have room for a bigger one without cutting a hole in the hood

[shadow88]

I got air filter pn 41-1200 for you flowing 1186 cfm.http://www.knfilters.com/search/prod...x?Prod=41-1200

I have rd-1200 flowing 791.28 cfm for me http://www.knfilters.com/search/prod...x?Prod=RD-1200

Damn your engine flows alot of air.

In order to do the math for the air filters use this formula for round filters - outer diameter x height x 3.14 x 6 = cfm
For cone filters use this one -- base diameter + top diameter / 2 x hieght x 3.14 x 6 = cfm

Those calculations are from K&N as well.

[Reeves]

Cool!

I came up with almost 1220 cfm for mine now!

---------- Post added at 12:14 PM ---------- Previous post was at 12:07 PM ----------

I got air filter pn 41-1200 for you flowing 1186 cfm.http://www.knfilters.com/search/prod...x?Prod=41-1200

I have rd-1200 flowing 791.28 cfm for me http://www.knfilters.com/search/prod...x?Prod=RD-1200

Damn your engine flows alot of air.

In order to do the math for the air filters use this formula for round filters - outer diameter x height x 3.14 x 6 = cfm
For cone filters use this one -- base diameter + top diameter / 2 x hieght x 3.14 x 6 = cfm

Those calculations are from K&N as well.

What is the calculation for panel filters?

[turbovanman²]

I got a 1000 cfm cone filter, I talked to AEM about what I was going for, he said that's more than enough, he said they use them on 1000 whp diesels,

[BadAssPerformance]

Good info. I sized and purchased my current one with SDAC member / K&N rep Gary Lorenz (Lorenz Racing)

[shadow88]

I never asked about the drop in panel filters because my airbox is long gone.

Jesus James, that engine sure consumes a lot of air! Well done!! It's nice to see this thread see the light of day and possibly help some of our members pick up a little more POWAH!!

[Reeves]

Makes me think I HAVE to fix my current air filter setup. My filter is WAY too small.....and I knew this before, but there is NO easy fix in my cramped up L-body. Thinking maybe a big panel filter in the cowl. Wonder if there is any rules against that since it's kind of behind the firewall?

Or maybe a small diameter, but LONG round filter.

Hmmm....

Plus my 4" to 3" elbow on the turbo needs to be replaced with 4" to 4" elbow....which I have waiting.

[Pat]

Make back to back runs with and without a filter at the track. That will tell the story for you.

Makes me think I HAVE to fix my current air filter setup. My filter is WAY too small.....and I knew this before, but there is NO easy fix in my cramped up L-body. Thinking maybe a big panel filter in the cowl. Wonder if there is any rules against that since it's kind of behind the firewall?

Or maybe a small diameter, but LONG round filter.

Hmmm....

Plus my 4" to 3" elbow on the turbo needs to be replaced with 4" to 4" elbow....which I have waiting.

[turbovanman²]

I've had trouble spooling my turbo at the track, just cleaned my filter and now i can easily brake torque to 20 psi, weird this is, I cleaned it in spring,

[Reeves]

Make back to back runs with and without a filter at the track. That will tell the story for you.

I have done that, kinda. I took off my entire CAI setup and ran with just an open turbo. Actually ran about a tenth slower. Figured it was due to hot air. This was a LONG time ago though, and it was on the SC6152 not the SC6262.

I would try to just take off the filter...but there is A LOT of debris off the slicks in that area. I have the filter in front of the left slick in the fender.

[ShelGame]

How does that calculation compare to looking up the max airflow for a given pressure ratio from the compressor map?

For me, the calculation above would give me...

((20psi/14.7)+1) x 153 x 5500/3456 = 575cfm

Byt the Mitsu comperssor map, at 20psi it will flow a maximum of ~0.18 m^3/s (and I'm extrapolating, the compressor map doesn't actually go that high); which equals about 380cfm. Big difference. At least in my case.

[zin]

Funny... You'd think they'd post that info up on their website! Couldn't find any tech, just product applications!

Mike

[shadow88]

Very true! It all came about in Detroit late night drunken tech session, so I called and found out when I got home. They really should, though.

[T-Bohn]

So I have been poking around reading this and thinking.

I found a site and have been trying to figure out flow rates of intercoolers. The best guess I have so far is that the stock S type intercooler is good for about 350 CFM.

If I am doing the math correctly the stock motor / redline / boost flows about 425 cfm.

Are the stock intercoolers really that undersized??

When everyone talks about going to larger intercoolers are they chasing max flow or is it surface area ( cool air exposure ) that warrants the larger size?

What about the same frontal area but twice as thick (more flow) but is the cooling capacity equal??

I may be in wrong thread for this but I am trying to understand what the numbers tell me.

[BadAssPerformance]

Funny... You'd think they'd post that info up on their website! Couldn't find any tech, just product applications!

Mike

Maybe this is beacause K&N has about a dozen air filter companies follwing their every move

[wallace]

I see 14.7 in the calculations you guys are using does that represent AFR?

[ShelGame]

I see 14.7 in the calculations you guys are using does that represent AFR?

No, it's psi. They're converting the boost pressure to an absolute pressure ratio...

[Juggy]

I see 14.7 in the calculations you guys are using does that represent AFR?

14.7psi (1 bar) is our atmospheric pressure on earth

[wallace]

14.7psi (1 bar) is our atmospheric pressure on earth

I deserved that it was a stupid question.