Welcome to the North American Subaru Impreza Owners Club Tuesday May 5, 2015
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
Here you can view your subscribed threads, work with private messages and edit your profile and preferences Home Registration is free! Visit the NASIOC Store NASIOC Rules Search Find other members Frequently Asked Questions Calendar Archive NASIOC Upgrade Garage Logout
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.
Reply
 
Thread Tools Display Modes
Old 10-09-2004, 11:53 PM   #1
kiltjim
Scooby Newbie
 
Member#: 60002
Join Date: Apr 2004
Location: PA, USA
Vehicle:
2000 Impreza OBS
Running at OC'ed 900MHz

Default Controlling intake diameter?

I want to have some more power while cruising around town, but I also want to maintain my gas mileage on the open highway.

I've removed my intakes as an experiment (left the filter on, though) and I've seen a slight increase in volume at FOT, and it seems like my scooby is a little more responsive. This could just be the placebo effect though. However, I have definetly seen a decrease in gas mileage though.

Is this right?

If it is...I was thinking about mounting a servo driven valve on the intake hose (after I put it back on). That way, I could run with a full open intake in town, and on the highway I could run it slightly closed to keep my GPM.

Am I crazy? Am I supposed to reset my ECU everytime I change the intake diameter to realize any change?

If I'm a dumb ass, please let the comments fly....
* Registered users of the site do not see these ads.
kiltjim is offline   Reply With Quote
Old 10-10-2004, 12:36 AM   #2
LetItSnow
Scooby Specialist
 
Member#: 38222
Join Date: Jun 2003
Chapter/Region: Tri-State
Location: Cicero, NY
Vehicle:
'10 &'12 Foresters
another Miata convert

Default

There are several variable length intakes as stock equipment right now... Porsche and Cadillac are using them, at the very least. What you would be doing would not be far different, except that yours would vary much less often (the production ones are RPM based).

It would be an interesting project, at least. With a little more research, you could probably figure out the optimum intake runner for the RPM you typically run on the highway
LetItSnow is offline   Reply With Quote
Old 10-10-2004, 10:15 AM   #3
orndog
Scooby Specialist
 
Member#: 34670
Join Date: Mar 2003
Chapter/Region: South East
Location: Atlanta
Vehicle:
2013 No gears!
Saltine American

Default

Go with a proper CAI. I would think your feelings of power increase would be due to 2 things, one being the reduced restriction but the other being the increased sound. Reduced mileage will also be due to 2 things, you hitting the gas more and the car inhaling hot air from the engine bay.
orndog is offline   Reply With Quote
Old 10-10-2004, 10:23 AM   #4
kiltjim
Scooby Newbie
 
Member#: 60002
Join Date: Apr 2004
Location: PA, USA
Vehicle:
2000 Impreza OBS
Running at OC'ed 900MHz

Default

Quote:
Originally Posted by orndog
Reduced mileage will also be due to 2 things, you hitting the gas more and the car inhaling hot air from the engine bay.
See, that's what I was thinking. Until I did a completely unbiased test, and drove about 6 hours across state. When I figured out my gas mileage, it had dropped from 36 MPG (my original, when I bought the car, same trip) to 26 MPG (with the open intake).

I guess it could be from the hot air. So, I was thinking I would get the Cobb CAI, like I originally planned, but put the valve into the middle of it, and see what would happen. This way, I won't be sucking hot air, and I will be able to control intake availability. I just hope I can figure a way to do it without destroying the CAI.
kiltjim is offline   Reply With Quote
Old 10-10-2004, 12:28 PM   #5
nySulli
Scooby Specialist
 
Member#: 32617
Join Date: Feb 2003
Chapter/Region: Tri-State
Location: NY
Vehicle:
2008 STi
DGM

Default

well inhaling hot air shouldn't effect your gas mileage, but that much of a difference i have a hard time accepting is from just taking off the intake, i've heard of people losing 2-4 mpg with a cobb intake, but not 10

but i like the idea, what about just making 2 split pipes, with a y-fitting, and putting a valve or gate mechanism that you can open and close remotely, or some type of servo works as well in just the 1 side, leaving the other section unaltered, actually you could use both of the holes on the right of the engine bay to get cold air for each pipe individually
nySulli is offline   Reply With Quote
Old 10-10-2004, 05:14 PM   #6
RS_to_WRX_swap
Scooby Specialist
 
Member#: 40337
Join Date: Jul 2003
Chapter/Region: BAIC
Location: Bay Area
Vehicle:
95 L Coupe Swapped
99 Outback

Default

I have tried stock (2.5in), 2.5 in straight pipe, and 3in straight pipe with a modified air box. i think you would be most pleased with my "version #1" intake (2.5in straight pipe with stock air box), see link. I have my old one i need to get rid of. First person at my door with a 6pack gets it.

You must reset the ECU after any engine mod thats affects the breathing of the motor. This way it only takes about a tank of gas for your gas mileage to become reavent, and to gauge power gains. When i went to 3 inch intake piping it took the car a LONG time to learn the low rpms when the the throttle was stabed. But after a full tank of gas i could say the car lost NO low end, and now the last 2k rpm before redline the car all out screams.

More info on my intakes, old and new here: http://forums.nasioc.com/forums/showthread.php?t=604352

Last edited by RS_to_WRX_swap; 10-10-2004 at 05:23 PM.
RS_to_WRX_swap is offline   Reply With Quote
Old 10-11-2004, 04:52 AM   #7
RyansJDMgc8
Scooby Newbie
 
Member#: 65462
Join Date: Jul 2004
Location: Riverside CA USA
Vehicle:
01' 2.5RS
Silver/Carbon Fiber

Default

I used to drive a 1973 Chevy Nova with a fully built 396. I got about 6 MPG. Now that I have my Subaru, I dont even care about gas prices!
RyansJDMgc8 is offline   Reply With Quote
Old 10-11-2004, 11:28 AM   #8
kiltjim
Scooby Newbie
 
Member#: 60002
Join Date: Apr 2004
Location: PA, USA
Vehicle:
2000 Impreza OBS
Running at OC'ed 900MHz

Default

I know I'm still getting better gas mileage than alot of cars out there. But I want my 36 MPG back! I guess if I'm not going to do any harm to the engine, I could always just try it, when I have access to my garage. I'll keep you all posted on the outcome, if you're interested.
kiltjim 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Hks cpu controlled variable diameter exhaust system kenlee General Community 1 07-02-2008 01:22 AM
Intake diameter WRX06 Newbies & FAQs 1 08-02-2005 12:34 AM
What is the stock intake diameter? TexRex2002 Factory 2.0L Turbo Powertrain (EJ Series Factory 2.0L Turbo) 13 09-16-2003 06:30 PM
Intake diameter vs throttle body diameter Kevin Thomas Normally Aspirated Powertrain 0 03-03-2002 07:46 PM
Intake diameter and airflow question Kevin Thomas Normally Aspirated Powertrain 4 11-19-2001 06:13 AM


All times are GMT -4. The time now is 09:05 PM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2015, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2015 Axivo Inc.
Copyright ©1999 - 2014, North American Subaru Impreza Owners Club, Inc.