The banner above is an advertisment - if it asks you to download software, please ignore.
Site News - 7/1: Members: Log In to See Fewer Ads! | 5/28: SAAB Evolutions/TSN T-Shirts $14
[General | Members | C900 | 9000 | NG900 & OG93 | 93 | 95 | NG95 | 99 | Sonett | Vintage Models | Clubs | Other Cars | FAQs | Gifts | Member Photo Galleries | Member Directory | Classifieds | Manuals | *Buddy Registry | *Mileage Registry | Polls | What's New | Raffle | Photo of the Month | Sponsors]

NG900 & OG93 Bulletin Board
1994-2002 [Subscribe to Daily Digest]
(Search Author's Posts: e.g. Keyword:username)*Members Only

[Main NG900 & OG93 Bulletin Board | BBFAQ | Prev by Date | Next by Date | Post Followup ] Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Re: valve timing and engine speed. general question.
Like This Post: - Subscribe to Daily Digest for this Bulletin Board
Posted by Dean (more from Dean) on Mon, 27 Oct 2003 08:21:53 Share Post by Email
In Reply to: valve timing and engine speed. general question., gray man, Sun, 26 Oct 2003 17:10:12
Alert me when someone posts in this thread:
Members do not see ads below this line. - Help Keep This Site Online - Signup

Turbo generally have different considerations than N/A engines.

The intake maanifold needs to have a plenum to store compressed air and the runners are short. So you don't get long runners to enhance low end torque. When the exhaust valve opens, the air in the plenumn rushes through the short runner to charge the cylinder (like a discharging capacitor). It is forced, not sucked in. You get a broad torque band from the turbo charging, instead of a modest torque that is optimal a one RPM range.

The turbo's turbine needs to be near the cylinder head. So the exaust manifold is short. The lengths are too short to have any value for tuning, and on boost, at 15 PSI of boost the exhaust backpressure might be 30 PSI or more. So its so far away from N/A exhaust system tuning priciples that there is hardly anthing in common.

Also note that the high pressures in the exhaust manifold increase the density and velocity of the gases that flow through it. So this makes the smallish passages in the manifold not as nasty as it appears.

You want to lower intake and exhaust restrictions as this lowers the exhaust backpressure for any given level of boost. That increases power directly by reducing the back pressure that the pistons see during the exhaust stroke. And note that with these high back pressures, that the residual gas in the cumbustion chamber will expand and this reduces volumentic efficiency as well.

The best things that you can do to increase the VE is to get a low restriction filter, mod the air box, remove the turbo compressor disharge silencer and rework the TB and fit a Sports exhaust. A Viggen IC is the next logical step after that. Then there is increase boost.

Remember that the turbo boost is not made by the turbo for free. The pistons are transfering shaft HP to the exhaust gases to push it through the turbine at pressures of 30 PSI or more sometimes.

posted by 207.43.195...
Posts in this Thread:
Alert me when someone posts in this thread:
Members do not see ads below this line. - Help Keep This Site Online - Signup
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 - Members see fewer ads. - Latest Member Gallery Photos
E-Mail: (Optional)
Re-Enter E-Mail: (Confidential & Secure - Not revealed to other users!)
Note: Please check your spam folder for BB responses.

Subject:

Posting rules are simple - No for sale/wanted ads may be posted here - use the site classifieds.
You may not cross-post your message to multiple BBs.
Not permitted: political/religious topics and being disrespectful (personal attacks, insults, etc...).
 Site Members do not see any red text, inline ad links, bottom of page anchor ads, box ads, or anti-spam check.

Message: (please no for sale/wanted classifieds - post those in the Saabnet.com Classifieds)
Links are now automatically made active, no need for any special code (or use the Option Link field below) - don't put links in () or end with a '.'
To add inline images to your post, use [img]http://www.domain.com/img.jpg[endimg] (or use the Optional Image Link field below).

Links are now automatically made active, no need for any special code (or use the Option Link field below) - don't put links in () or end with a '.'
To add inline images to your post above, 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/)
Link Title: (Optional)
Optional Photo/Image Link: (e.g. http://www.saabnet.com/img.jpg)
Photo/Image to Upload: (Please be patient while file uploads)



StateOfNine.com
SaabClub.com
Jak Stoll Performance
M Car Covers
Ad Available

The content on this site may not be republished without permission. Copyright © 1988-2024 - The Saab Network - saabnet.com.
For usage guidelines, see the Mission & Privacy Notice.
[Contact | Site Map | Saabnet.com on Facebook | Saabnet.com on Twitter | Shop Amazon via TSN | Site Donations]

Random Saabnet.com Member Gallery Photos (Click Image)
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 | Run Club Menlo Park | ScreenBot


Site Members do not see red text instructions, bottom of the page anchor ads, or box ads.
Click here to see all the Site Membership Benefits!