User Tag List

Thanks Thanks:  0
Likes Likes:  0
Page 1 of 3 123 LastLast
Results 1 to 10 of 23

Thread: Size matters, os so i thought with exhausts

  1. #1
    Regular Member
    Join Date
    Jun 2009
    Location
    Mundesley, Norfolk
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Exclamation Size matters, os so i thought with exhausts

    I'm new to the site and to modding a diesel. I've had the petrol head stage and modded a few petrol cars. I've looked through a few posts about exhaust sizes and several people worried about back pressure on there turbo diesels. From my petrol days i re-call various tuners telling me on turbo'd cars that the turbo itself creats all the back pressure the car needs so oversized donb't matter - i'd have thought it would be the same on diesel - right or wrong ? ? ? ?

  2. #2
    Regular Member parsco's Avatar
    Join Date
    Sep 2008
    Location
    Cambridgeshire
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    Correct, diesels with a turbo on do not require back pressure to run effectively. You could have no exhaust on a diesel and if anything it would run better (just be really loud).
    Where as petrols use back pressure from the exhaust to run better

  3. #3
    Regular Member
    Join Date
    Jun 2009
    Location
    Mundesley, Norfolk
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    Thank you mate - knew it was right for petrol cars and assumed so for derv but with so many on this site not sure i needed to ask

  4. #4
    Regular Member Ste's Avatar
    Join Date
    Jul 2005
    Location
    ..... Driving the Jaguar XF
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    It's not really right for petrol either.

    Some exhausts 'extract' the exhaust gases by the inherent design causing a low pressure on the port when the exhaust valve is about to open - but this only works for specific engine speeds and harmonics.

    Engines are set up to run on the given back pressure, so removing it will make the engine run worse on it's current settings (usually) - but by changing those settings, better performance can be obtained. I would doubt that this is something you could do easily / cost effectively with modern engines and electronics. This is one reason why people change exhausts etc BEFORE an engine remap....

  5. #5
    Regular Member
    Join Date
    Jun 2006
    Location
    Kirkintilloch, Scotland
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    I'm a bit confused. (not a difficult thing to achieve with me).

    Does my car - a 2004 2.2 petrol auto direct estate - require some sort of balanced back pressure on the exhaust?

    The reason I ask is that I recently had a bespoke stainless steel exhaust fitted to the vehicle. I went for the bespoke system on the grounds of cost and my then belief that there was no need on the vehicle for some sort of balanced exhaust system and that the less the resistance offered by the system the better.

    Dave

  6. #6
    Regular Member
    Join Date
    Nov 2008
    Location
    Chester
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    Always thought the "Back Pressure" thing was a Fred in his shed term. My assumption would be that a massive exhaust on say a saxo (as an obvious example) would reduce power output as the exhaust velocity would drop massively meaning that exhaust gases aren't extracted effeciently and the engine has to pump a much larger mass of air. Also the reasons Ste mentions.

  7. #7
    Full Member Big Sig's Avatar
    Join Date
    Aug 2006
    Location
    Is a very naughty boy
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    The right back pressure helps keep the torque figure up IIRC
    Now I need a turbo to keep up!

  8. #8
    Regular Member john_k_sri's Avatar
    Join Date
    Oct 2006
    Location
    Waterloo, Liverpool
    Post Thanks / Like
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    1 Post(s)
    Tagged
    0 Thread(s)

    Default

    Am I right to assume that changing the exhaust for something, bigger louder or de-catted may not always get the desired results on a turbo petrol engine? I ask this because the main benefit from uprated exhausts has more to do with sound styling and aesthetics than with driveability or out-and-out performance.
    Last edited by john_k_sri; 4th June 2009 at 17:28. Reason: amendment

  9. #9
    Regular Member Ste's Avatar
    Join Date
    Jul 2005
    Location
    ..... Driving the Jaguar XF
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    0 Post(s)
    Tagged
    0 Thread(s)

    Default

    If you have the ability to utilise any reduction in back pressure from 'performance' or 'sport' exhausts, then you will get more power at the wheels as less power is used to push exhaust gases through the exhaust system (which takes energy from the engine, so reducing power at wheels)

  10. #10
    Regular Member rushy's Avatar
    Join Date
    Jul 2005
    Location
    Old School Vectra-C.Com. Residing in sunny Leeds.
    Post Thanks / Like
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)
    StatsVehicle Info
    Post Thanks / Like
    Mentioned
    2 Post(s)
    Tagged
    0 Thread(s)

    Default

    Quote Originally Posted by DaveG View Post
    I'm a bit confused. (not a difficult thing to achieve with me).

    Does my car - a 2004 2.2 petrol auto direct estate - require some sort of balanced back pressure on the exhaust?

    The reason I ask is that I recently had a bespoke stainless steel exhaust fitted to the vehicle. I went for the bespoke system on the grounds of cost and my then belief that there was no need on the vehicle for some sort of balanced exhaust system and that the less the resistance offered by the system the better.

    Dave
    Quote Originally Posted by Big Sig View Post
    The right back pressure helps keep the torque figure up IIRC
    If you have a twin fitted the larges bore size that really works for the 2.2 is 2.5 inch if I remember rightly, then at the Y the two pipes need to the be reduced in size. These small engined cars like 1.1 and so on really rely on back pressure thats why they have pea shooters fitted. Makes me laugh when they have big bore's fitted. Mega horsepower cars that run high revs all the time want as little as possible back pressure, hence why they run like a bag of spanners for regular road driving.

Page 1 of 3 123 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Wheel size and tyre size
    By DSmiddy in forum Vectra C / Signum Car Chat
    Replies: 15
    Last Post: 14th December 2011, 19:19
  2. vec b/c 2.2 exhausts
    By denzilbud in forum Vectra C / Signum Car Chat
    Replies: 2
    Last Post: 22nd July 2009, 11:40
  3. exhausts
    By billyyoung in forum Vectra C / Signum Car Chat
    Replies: 9
    Last Post: 11th November 2007, 20:34
  4. Exhausts
    By Steve-E in forum Vectra C / Signum Car Chat
    Replies: 2
    Last Post: 28th March 2006, 20:40
  5. new exhausts
    By Beavis in forum Vectra C / Signum Car Chat
    Replies: 10
    Last Post: 28th March 2006, 17:30

Visitors found this page by searching for:

Nobody landed on this page from a search engine, yet!

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •