Welcome to the North American Subaru Impreza Owners Club Tuesday July 25, 2017
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC Technical > Normally Aspirated Powertrain

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. 
Thread Tools Display Modes
Old 02-22-2001, 10:39 PM   #1
Scooby Newbie
Member#: 4411
Join Date: Feb 2001
Location: Appleton, WI
2001 Impreza 2.5 RS

Thumbs up 2.5" tubing for intakes (solution possibly)

I am new to the board so obviously I havent read everything you guys have been talking about on the subject of intakes. Reading all of the current talk on intakes makes me think of two things that have made the WeaponR, JC Sports not work so well under 3500 rpms.

1) Tubing was too short to even create velocity.
2) 3" tubing was used in these intakes not helping air velocity also.

My question is, what do you guys think about an intake that eliminated the stock air box, was 2.5" in diameter in tubing size, and sat right behind the front left headlight??

Ya it would still suck in cold air, but the two issues I had addressed that may be affecting good air scaveging could be solved. If this has already been tested or proven wrong, feel free to imform me. I always want to learn something new. Just thought I'd throw this one out there!

* Registered users of the site do not see these ads.
impRSa01 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 02-22-2001, 11:02 PM   #2
Scooby Specialist
Member#: 3097
Join Date: Nov 2000
Chapter/Region: NWIC
Location: www.rs25.com Beaverton, OR
2013 Ford Focus ST
Performance Blue


Larry Ganz (www.imprezars.com) has already done a cold air intake in the 2.5" and 3". Here's the 2.5" (on my car ):
<IMG SRC="http://www.i-club.com/ubb-files/image_uploads/GanzFlow.jpg" border=0>
Here's the 3" on Larry's site:
<IMG SRC="http://www.imprezars.com/images/version5/rev5intakeenginebayclose.jpg" border=0>
Great intake, by the way! His retains the stock airbox, preserving the low-end torque, and you can't beat the price!

edit: P.S.- Welcome to the club!

[This message has been edited by HondaH8er (edited February 22, 2001).]
HondaH8er is offline   Reply With Quote
Old 02-22-2001, 11:15 PM   #3

Member#: 922
Join Date: Feb 2000
Chapter/Region: MWSOC
Location: Schaumburg, IL
16 WRX (white)
04 FXT (red)


It's not the velocity that is the concern. Velocity really changes the high end of the powerband more then anything, while the pressure drop is what kills the low end.

With the stock intake plenum you have a small reserve of air that is pulled from first, so you get enough air to run the engine well down low without dropping the pressure too much in the intake plenum causing it to have to pull air harder through the tubing, creating torque. When it does have to pull harder (tube intakes) you get much better high end with a loss of low end because the engine has to put so much effort towards getting air in the first place.

What kinda intake is a good trade off? Larry's is ok. Mine is pretty good too - http://8complex.mwic.org/intake/
8Complex is offline   Reply With Quote
Old 02-22-2001, 11:38 PM   #4
Scooby Newbie
Member#: 4411
Join Date: Feb 2001
Location: Appleton, WI
2001 Impreza 2.5 RS



I get what you are saying about the engine having to work harder, but isn't that where the velocity comes into play. Think from my point of view. Either way, the air has got to first start to go into your intake no matter what setup you have. If the engine is sucking it in always, why would air be left around in the intake for under 3500 rpm situations.

Isn't the intake just like the exhaust. I know for the exhaust, that the best exhaust has the lowest amount of backpressure possible without losing it completely. Why would velocity matter for the intake when if the tubing is smaller it will get to the engine faster for low rpm cycles. And I don't mean so small that the engine has to over work to get the air in like you were mentioning. Just a tube size that is practical, yet aftermarket in design.

Thanks for all the help 8Complex.

P.S- I checked out your design. Looks like an N/A intercooler. Wonder if you would see more gains with an aluminum N/A intercooler setup?
impRSa01 is offline   Reply With Quote
Old 02-23-2001, 05:17 AM   #5
Scooby Specialist
Member#: 3139
Join Date: Dec 2000
Chapter/Region: RMIC
Location: SLC Utah
2001 Dodge Pikumup
& 08 Triumph Speed Triple


Cobb Tuning uses what looks like less than 3" pipeing on his intake. Maybe for the reason of keeping velocity higher.
<IMG SRC="http://www.cobbtuning.com/images/ct-cai2.jpg" border=0>
judging by the fact that the reducer is right after the filter, and the piping is about the same size as the throttle body, it seems around 2.5". Just an educated guess though.

scoobiejosh is offline   Reply With Quote

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 07:36 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.