Premise for this - Saabnet.com Bulletin Board


[General | Members | C900 | 9000 | NG900 & OG93 | 93 | 95 | NG95 | 99 | Sonett | Vintage Models | Performance | Detail | Clubs & SOC | Other Cars | Books Movies & Music | Chat | FAQs | Gifts | Member Photo Galleries | Member Directory | Classifieds | Service/Mechs | Manuals | *Buddy Registry | *Mileage Registry | Polls | What's New | Raffle | Photo of the Month | Sponsors]

Performance Bulletin Board
Search:
(Search Author's Posts: e.g. Keyword:Author)*Members Only


[Main Performance Bulletin Board | Post Followup | BBFAQ ] [ Prev by Date ] [ Next by Date ] Member Login / Signup [Most Recently Edited Saabnet.com Photo Galleries]
Premise for this
Posted by thetallguy [Email] (#1698) [Profile/Gallery] (more from thetallguy) on Wed, 25 Feb 2015 07:07:46

In Reply to: Re: Anyone running the GFB #T9301 Diverter Valve?, Simon S, Sun, 22 Feb 2015 10:32:38
Alert me when someone posts in this thread:

Both control valves (Bosch and GFB) remain closed on boost by using boost pressure to hold the valve shut. Pressure remains equal on both sides of the valve as long as the throttle butterfly is open. Once the throttle snaps shut on a deceleration event or gear shift, pressure in the intake drops below atmosphere and the sprung seal opens; the seal broken by the pressure differential.This is why the Bosch begins to vent before you might suspect based on the boost gauge. The premise that modern turbos spool more quickly and therefore maintaining the pressure in the intake/intercooler is "better" than maintaining turbine speed appears suspect. If one is using a higher performance turbocharger which is generally characterized by a larger compressor wheel (more weight), pumping more air volume (more weight), with more associated "lag" at a elevated pressure (higher than stock),then maintaining turbine speed would appear, in my opinion , to remain a viable concern. Regaining lost rotational speed takes time! This is "probably" best addressed by quick venting. Quick venting allows the turbine to maintain its speed and avoid a "stall". Decelerating a turbo quickly is hard on the turbine shaft and increases lag time. The amount of time to re-spool is based upon the weight of the rotating assembly,bearing frictional losses, the target pressure one needs to achieve the desired acceleration, the exhaust gas heat available at that specific moment in time, exhaust gas pressure, and the initial turbine wheel speed.In the case of the GFB, the compressor wheel would also be fighting the alleged elevated intake pressure although equalization would happen so quickly that it would count for almost nothing. From what I've read, maintaining the compressor spool speed/energy results in the least amount of "lag" between most boosting events. Those using a larger turbo or elevated boost levels on a stock system probably still have the same problems associated with an "older" design. Quick venting is best accomplished (on Bosch) by using the least amount of spring tension possible and the sealing diaphragm's "pull" as the pressure differential drops . The limiting factor, as I recall, being a need for the valve to resist the vacuum on deceleration (hooting). It's possible the GFB design negates a need to resist vacuum; that, however, is not the sales pitch here. So the answer is...it depends: on stock turbo VS higher performance turbo and the actual boosting event in question. By GFB's own admission the turbine's speed on re-spool is lower. This is not a good thing!The risk of deceleration of the turbine could be a problem. Also not good. If the GFB's design allowed less spring tension or no spring tension on deceleration then that, in my opinion, would be "more better". The Bosch unit is very very good in all design aspects to insure fast venting. Just no CNC goodness. IMO.

It would be nice if you could maintain pressure in the intake AND preserve turbine speed...the search continues. Possibly why the newer modern turbo come with the recirculating valve built into the compressor housing.I see this function coming under computer control in the future...possibly already available on Jags; perhaps someone has some info on this.

->Posting last edited on Wed, 25 Feb 2015 07:30:03.
Posts in this Thread:
Alert me when someone posts in this thread:

Post a Followup

No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.

Name: Member Login / Signup [Most Recently Edited Saabnet.com Photo Galleries]
E-Mail: (Optional)
Re-Enter E-Mail: (Confidential & Secure - Not revealed to other users!)
Note: Please check your spam folder for BB responses.
If you use GMail, follow these instructions from Google so that they appear in your regular inbox.

Subject:

Posting rules are simple - No for sale/wanted ads or live auctions may be here - use the classifieds.
You may not cross-post your message to multiple BBs.
Personal attacks, insults, or flaming are not allowed.
Site Members do not see any red text, inline ad links, skyscraper ads, box ads, nor anti-spam check.

Message: (please no for sale/wanted classifieds - post those in the TSN Classifieds)
To add inline links to your post, use [link]http://www.domain.com/[endlink] or use the Optional fields below.
To add inline images to your post, use [img]http://www.domain.com/img.jpg[endimg] or use the Optional Image Link field below.


Optional Link: (e.g. http://www.saabnet.com/)
To promote your own Saab site here, you must have a link back to The Saab Network.
Link Title: (Optional)
Optional Image Link: (e.g. http://www.saabnet.com/img.jpg)





The content on this site may not be republished without permission. Copyright © 1988-2018 - The Saab Network - saabnet.com.
For usage guidelines, see the Saabnet.com Mission and Purpose Page.
[Contact | Site Map | Saabnet.com on Facebook | Saabnet.com on Twitter | Shop Amazon via TSN | Site Donations]

This is a moderated bulletin board - Posting is a privilege, not a right. Unsolicited commercial postings are not allowed (no Spam). Please, no For Sale or Wanted postings, SERIOUSLY. Classifieds are to be listed in The Saab Network Classifieds pages. This is a problem solving forum for over 250,000 Saab owners, so expect to see problems discussed here even though our cars are generally very reliable. This is not an anything goes type of forum. Saabnet.com has been a moderated forum since 1988. For usage guidelines, see the Saabnet.com Mission and Purpose Page. Please remember that you are not anonymous. Site Contact | Site Donations | Other Sites by SP - Poverty2Prosperity.org
Your address is: 54.198.103.13 - Using CCBot/2.0 (https://commoncrawl.org/faq/) - Logged.

Site Members do not see red text instructions, skyscraper, nor box ads.
Click here to see all the Site Membership Benefits!