Welcome to the North American Subaru Impreza Owners Club Monday December 11, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Go Back   NASIOC > NASIOC Technical > Engine Management & Tuning > Open Source Reflashes

Welcome to NASIOC - The world's largest online community for Subaru enthusiasts!
Welcome to the NASIOC.com Subaru forum.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, free of charge, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, so please join our community today!

If you have any problems with the registration process or your account login, please contact us.
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 07-11-2017, 06:59 PM   #1
pcampbell
Scooby Newbie
 
Member#: 437670
Join Date: Jan 2016
Vehicle:
2005 2.5 SC OB

Default MAF scaling

I'm going from stock 2.6" to 2.75" ID MAF housing.

The formula I read on this forum is 2.75*2.75 / 2.6*2.6.
I am way lean using the formula everyone suggests, which only gives me a 11.8% increase.

Why wouldn't you use the area of a circle formula?

PI R squared for 2.6 ID = 8.97
PI R squared for 2.75 ID = 11.12

I get very close to stock (low single digit learning) with a 23% increase calculated using area of a circle formula.
* Registered users of the site do not see these ads.

Last edited by pcampbell; 07-11-2017 at 08:33 PM.
pcampbell is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 07-12-2017, 04:32 PM   #2
86Dreams
Scooby Specialist
 
Member#: 385256
Join Date: Mar 2014
Chapter/Region: Tri-State
Location: Harriman NY
Vehicle:
02 WRX S204 swap

Default

in the end you SHOULD get the same ratio.
pi r^2 = pi/4 D^2

in either case the pi or the pi/4 should cancel
D1=2.6
r1=1.3
pi=3.14159
pi*r*r=5.309 = A1
pi/4*D1^2 = 5.309

D2=2.75
r2=1.375
pi*r*r=5.939 =A2

scaling=A2/A1=1.1187 = (2.75*2.75)/(2.6*2.6)
vs
11.12/8.97=1.239


What thread does this formula come from?

Last edited by 86Dreams; 07-12-2017 at 04:48 PM.
86Dreams is offline   Reply With Quote
Old 07-12-2017, 07:55 PM   #3
pcampbell
Scooby Newbie
 
Member#: 437670
Join Date: Jan 2016
Vehicle:
2005 2.5 SC OB

Default

Heh, I think I squared it one too many times..... Not sure what on earth I was doing . I agree with your math.

But scaling it this way (*1.1187) put me very lean (big positive AF learning).

I kept increasing it until learning was around 0 and ended up around 23% which seems a crazy big difference for such a small difference in diameter. Could it really flow this much better? Smooth aluminum vs plastic/rubber with ribs or whatever? New MAF housing has an air straightener on it.. Maybe it "reads" more air because it's all lined up?

Last edited by pcampbell; 07-12-2017 at 08:22 PM.
pcampbell is offline   Reply With Quote
Old 07-12-2017, 08:07 PM   #4
CarmelValleyWRX
Scooby Newbie
 
Member#: 453872
Join Date: Sep 2016
Vehicle:
2005 wrx wagon
48w

Default

you use the first formula if your intake is a square.
CarmelValleyWRX is offline   Reply With Quote
Old 08-30-2017, 05:56 PM   #5
FUNGC
Scooby Newbie
 
Member#: 373156
Join Date: Nov 2013
Default

Quote:
Originally Posted by pcampbell View Post
Heh, I think I squared it one too many times..... Not sure what on earth I was doing . I agree with your math.

But scaling it this way (*1.1187) put me very lean (big positive AF learning).

I kept increasing it until learning was around 0 and ended up around 23% which seems a crazy big difference for such a small difference in diameter. Could it really flow this much better? Smooth aluminum vs plastic/rubber with ribs or whatever? New MAF housing has an air straightener on it.. Maybe it "reads" more air because it's all lined up?
Your math shows that the new intake section area is 23.9% larger so it falls inline with why you ended up around 23% scaling.
FUNGC is offline   Reply With Quote
Old 09-02-2017, 08:28 PM   #6
pcampbell
Scooby Newbie
 
Member#: 437670
Join Date: Jan 2016
Vehicle:
2005 2.5 SC OB

Default

Quote:
Originally Posted by FUNGC View Post
Your math shows that the new intake section area is 23.9% larger so it falls inline with why you ended up around 23% scaling.


My math was wrong. I went from 2.6 to 2.75" ID. Why I needed to scale so much bigger I don't know. The air straightener could have something to do with it.
pcampbell is offline   Reply With Quote
Old 09-03-2017, 08:14 AM   #7
jon7009
Scooby Newbie
 
Member#: 394646
Join Date: Jun 2014
Chapter/Region: NWIC
Location: Oregon
Vehicle:
2003 WRX Flex Fuel
EJ205 TD04L FMIC SD

Default

depending on what your air straightener is doing and where, it can have a dramatic difference in MAF scaling across the whole table.
jon7009 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 07:24 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2017 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.