Welcome to the North American Subaru Impreza Owners Club Sunday January 21, 2018
Home Forums WikiNASIOC Products Store Modifications Upgrade Garage
Go Back   NASIOC > NASIOC Technical > Engine Management & Tuning

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 04-21-2005, 09:59 PM   #1
Scooby Specialist
Member#: 75122
Join Date: Nov 2004
Chapter/Region: SCIC
Location: Im in a glass case of emotion
2005 Impreza WRX
Crystal Gray

Default How would you tune the VF39?

Just curious. I was looking at the Base map for the Stage2.5 COBB with the VF34. Im planning to get a 39 and modify the 34 map with the StreetTuner. Now, I know that there is more lag with the 39 but it does push more CFM's later. Just curious on how you would tune the vf39. Im not asking for super specifics, just curious on different theories. Understanding the characteristics of the VF39, how much boost would you run? Timing advance? Fuel ratio's and also theories. Im not looking for the ultimate tune or anything and I dont want this thread to turn into a "this theory is better than that one." Just looking to learn a bit more on different tuning methods. If you feel that your tuning secrets are too valuable to share then thats fine as well, just dont say, "my tune is better but Im not gonna tell you how its better."

Thanks a bunch


Here are the mods im working with.
STi "Pink" injectors
Walbro Fuel Pump
Perrin Light weight Pulley (Stock Size)
Helix CATTED Downpipe (3")
Stock Intermediate Pipe (2.5")
Stock USDM STi Axleback (2.5")
IC Hoses
California Piss pump 91 octane
* Registered users of the site do not see these ads.
darksands is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 04-21-2005, 11:39 PM   #2
Scooby Specialist
Member#: 56321
Join Date: Mar 2004
Chapter/Region: NESIC
Location: Hopkinton, MA
2006 Honda El Camino


Here's my $.02- I'm no pro by any means. I'm not responsible for anything

So here's what I would do- I'd start with the 2.5 map. It's already got turbo dynamics for the vf34 and the fueling should be close. Since the vf39 is going to run slightly less volume than the vf34, I'm guessing you are just going to run rich if anything.

From there, I'd work on getting boost right. Playing with the turbo dynamics has consumed much of my time, but maybe you'll have more luck. Try doing pulls in different gears to make sure that you aren't overboosting or spiking. Start with a conservative boost level and get things in good shape. Then start adding boost until you don't feel any benefit (eventually, the turbo is going to get out of it's effeciency range and you'll be blowing hot air, taking away power). If you have a road dyno, it would be helpful here. Make sure to keep an eye on IDCs, EGTs and KC/IT. You don't want your injectors to go static, your EGTs to go too high and you want to watch for the ECU pulling timing.

Next, I'd work on AFRs. I'd start by slowly pulling out fuel to see if it yields more power. You'll need to keep an eye on EGTs too. If you generally don't do pulls in higher gears, you can probably run the car a little leaner. EGTs won't have a chance to climb as much during pulls in lower gears, whereas the extended periods you'll see high loads in higher gears will cause them to climb, making you susceptible to det.

Then, I'd add in timing in places where it yields more power. After a certain point, you will not see additional power from additional timing (once you are past minimum best timing). If you continue to advance past that, you'll det. Again keep an eye on EGTS. Also, you might need to correct your boost a little bit since higher heat means higher velocity of exhaust gasses, which means your boost might increase a bit.

Yeah....and of course this all seems a lot simpler in theory than it is in practice. I think the biggest suggestion I can offer is to make small changes and make sure things are progressing the way you intend them to. Sometimes changes have effects that you may not have thought of.

Again, I could be 100% wrong, so anyone feel free to correct me. I'm just trying to share I'm actually pretty curious to see how the vf39 does on a 2.0L engine.

Also, I believe the stock maps are made for real 93 gas, so you might want to pull a few degrees of timing off to give yourself some headroom. Seems like the ECU will protect the car to some degree- as long as the changes are small. If you go and set your timing to 40 degrees across the board, then there's not much it can do.


Last edited by crazymikie; 04-21-2005 at 11:41 PM. Reason: Stupid CA Gas
crazymikie 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

Similar Threads
Thread Thread Starter Forum Replies Last Post
If you were Norv Turner, how would you play the Patriots Corn-Picker Off-Topic 77 01-18-2008 08:44 PM
Those who saw Dawn of the Dead: How would you rig the buses? Snoopy Off-Topic 43 11-21-2007 02:08 PM
How would you solve the awkward problems of the Tribeca? Diabolical1 CC Tribeca Forum 24 08-22-2005 02:38 PM
How would you describe the difference in handling of the USDM STi and the BMW 330i? Zoso General Community 4 01-04-2004 08:01 PM

All times are GMT -4. The time now is 07:28 AM.

Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2018 Axivo Inc.
Copyright ©1999 - 2017, North American Subaru Impreza Owners Club, Inc.