Welcome to the North American Subaru Impreza Owners Club Thursday March 28, 2024
Home Forums Images WikiNASIOC Products Store Modifications Upgrade Garage
NASIOC
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.







* As an Amazon Associate I earn from qualifying purchases. 
* Registered users of the site do not see these ads. 
Reply
 
Thread Tools Display Modes
Old 06-12-2022, 09:19 AM   #1
fasteddie313
Scooby Newbie
 
Member#: 530321
Join Date: Jun 2022
Default Boost taper why?

To my logic an engine is most likely to get det/knock at peak torque and lower RPM, less likely at RPM higher than peak torque, correct?

What’s the point of all this boost taper then? Is their a reason this is done so much on Subarus?
An excuse for the poor boost control of internal waste gates and boost reference bleeding boost control method? (Crap boost control method imo)

Or is it usually because people are running too small of turbos that will overspeed if they try to hold boost to redline? Like stock turbos, so you can max the turbo out all the way from down low to up top, but have to taper the boost down up top to not go over the turbos limits?

What’s up with this?


I just spent a lot of time experimenting and set up a new MBC boost control setup and I’m coming right up to about 14-15 psi at spool and tapering UP to about 18 psi by redline..

No spike at first boost at all.. No boost creep.. No FLUTTER!
Solid steady hard boost like boost should be..

In ALL GEARS! “Not enough load in low gears to blah blah blah” nope..
Less load in low gears, and faster rate of change, so your fancy EBC has different effects in different gears, I imagine unless you want to tune boost for every gear, which would take hours..

Yes I do want Part Throttle Full Boost.. I’m used to it, it’s what I like, it’s how a turbo should feel (to me)..
I DO NOT want some computer trying to give me half boost if my TPS is only at 50% or whatever.. Because it feels unnatural, it takes time for it to up the boost again when increasing TPS, and is just another tuning variable that could mess up with way too much variable to account for..

VF48 turbo on an EJ205..
This should not be over the turbos limits I do not believe.. 18psi at redline..

Am I missing something?
* Registered users of the site do not see these ads.
fasteddie313 is offline   Reply With Quote
Sponsored Links
* Registered users of the site do not see these ads.
Old 06-12-2022, 11:01 AM   #2
benflynn
Scooby Specialist
 
Member#: 515308
Join Date: Jun 2020
Default

Cause the turbo won’t flow enough air as the rpm go up.
benflynn is offline   Reply With Quote
Old 06-12-2022, 07:24 PM   #3
K3rm1tth3fr0g
Scooby Specialist
 
Member#: 508105
Join Date: Nov 2019
Chapter/Region: NWIC
Location: Greater Seattle Area
Vehicle:
Link G4X flex tuned
02' EJ205 20G 6MT wagon

Default

It's mostly because the turbos that come on the WRX/STi are so small. Even the vf48 is a pretty small turbo despite it being pretty sluggish on a 2.0L - it just isn't efficient at 6.5K RPM @ 20 psi.

My 20G-XTR carries 24 psi to redline on my stock USDM 205 using a 3 port.

And part throttle full boost is objectively dumb

Last edited by K3rm1tth3fr0g; 06-13-2022 at 09:00 PM.
K3rm1tth3fr0g 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 08:20 AM.


Powered by vBulletin® Version 3.7.0
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Powered by Searchlight © 2024 Axivo Inc.
Copyright ©1999 - 2019, North American Subaru Impreza Owners Club, Inc.

As an Amazon Associate I earn from qualifying purchases.

When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission
Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.