Exhaust back pressure - Page 2





Page 2 of 2 FirstFirst 1 2
Results 21 to 35 of 35
  1. #21
    Join Date
    May 2009
    Location
    Hillcrest, Malaysia
    Age
    63
    Posts
    18,855
    Thanked: 6464

    Default Re: Exhaust back pressure

    Quote Originally Posted by grips View Post
    Very true.

    One must remember that tech developed by racers and performance divisions have found their way into production engines.

    It is still amazing to see what companies like Cosworth have achieved 40 to 50 years ago.

    The basics of performance have however not changed over the many years. You need to fill the camber as quickly as possible with the largest volume of air/fuel it can take. Then you need to get rid off that as quickly as possible.

    So in the end it does not matter if it is a carburetor or injection it is about the time and volume of the fill.

    Modern tech is just way easier to control and can make split second adjustments.
    The difference is that the modern cars, start easily, idle nicely, pull from cold, are reliable, fuel efficient and pull throughout the powerband AND have a high output. Things like the Cosworth only achieved ONE of those parameters.
    Cheers

    ZS5KAD
    3 V8's
    NA TwinTurbo SuperCharger
    A V6 and an inline 4

    The frogs are starting to notice that the water is getting warm but it is already too hot to do anything about it.....

  2. The Following User Says Thank You to Fluffy For This Useful Post:


  3. #22
    Join Date
    Dec 2009
    Location
    Centurion
    Age
    47
    Posts
    1,156
    Thanked: 37

    Default Re: Exhaust back pressure

    "Here is an analogy...a garden hose without a spray nozzle on it. If you let the water just run unrestricted out of the hose it flows out limply at a rather slow rate. However, if you take your finger and cover part of the opening, the water will spray out at a much much faster rate."

    when I read this I realised the author of the doc does not really understand flow rates at all......
    JT

  4. #23
    Join Date
    Nov 2007
    Location
    Kathu
    Age
    59
    Posts
    9,311
    Thanked: 2839

    Default Re: Exhaust back pressure

    Quote Originally Posted by jelo View Post
    the big issue with old school fixed cam timing and stuck manifold lengths was you ALWAYS had a power band effect : a torque cam and tuned headers and inlet manifold would give say peak torque @ 1,500rpm. This engine would NEVER rev.

    Similarly, that Cosworth had to have its clutch slipped so that it could pull away. NOTHING under probably 4,500rpm?
    That was the reason for split duration cams. When you ever come to Kathu I will give you a ride in one of my v8`s.

    I can put foot from 1500rpm in till 7000rpm. I do not want to start the old school vs new tech fight all over again.

    New tech is the future and that is not arguable.

    If I am allowed to compare a modern Lexus 1UZ vvti with one of my olds school v8`s. The old school v8 will kill it from 1500rpm to 7000. Yes I can slam 7000 with the aid the roller cams and balanced rotating assy. I know it is not fair to compare 5.0l vs 4.0l. But then the 4.0l have all that modern tech.

    What about a forum challenge. You can build a modern normal aspirated v8 of 5.0l (You can stroke a Lexus to 5.0l)and I will build and old school v8. Then we put them on a engine dyno. We restrict the budget for the built to R100 000.00
    and start out with stock engines.
    It is not what you buy its what you build.

  5. #24
    Join Date
    Dec 2014
    Location
    Durban
    Age
    40
    Posts
    379
    Thanked: 191

    Default Re: Exhaust back pressure

    Quote Originally Posted by Woestynbrak View Post
    In my time most school lighties with their 2 stroke 50's found out the hard way that a 2 stroke exhaust is tuned to the engine and messing around with it will not help in their quest to increase top end from 83,2 km/h to an all time 50cc record of 84,1 km/h.

    It is basically the same principle that applies to tuned intake manifolds where the pulses are used to enhance the induction process.
    haha, i was one of those...
    "I am a hypocrite but i try not to be..."

  6. #25
    Join Date
    Nov 2007
    Location
    Kathu
    Age
    59
    Posts
    9,311
    Thanked: 2839

    Default Re: Exhaust back pressure

    Quote Originally Posted by Fluffy View Post
    The difference is that the modern cars, start easily, idle nicely, pull from cold, are reliable, fuel efficient and pull throughout the powerband AND have a high output. Things like the Cosworth only achieved ONE of those parameters.
    Fluffy I agree with all said. My thing is that some people make off all old engines as powerless hard starting unreliable stuff.
    One of the Ford Couriers in my business have been running flawless for more than 400 000km with a carburetor and start with the touch of the key.

    Yes old school stuff are dated new tech is way better, but the principal of how an engine works stays the same. Only the controls en design have changed.
    It is not what you buy its what you build.

  7. #26
    Join Date
    Dec 2013
    Location
    -
    Posts
    902
    Thanked: 17

    Default Re: Exhaust back pressure

    Quote Originally Posted by JTK_CPT View Post


    when I read this I realised the author of the doc does not really understand flow rates at all......
    Quite a number of technical inaccuracies in the article.

  8. #27
    Join Date
    Dec 2009
    Location
    Centurion
    Age
    47
    Posts
    1,156
    Thanked: 37

    Default Re: Exhaust back pressure

    Quote Originally Posted by jarnojvv View Post
    Quite a number of technical inaccuracies in the article.
    probably. I stopped at that statement as I realised I would be wasting my time reading further...
    JT

  9. #28
    Join Date
    Nov 2007
    Location
    Kathu
    Age
    59
    Posts
    9,311
    Thanked: 2839

    Default Re: Exhaust back pressure

    Quote Originally Posted by JTK_CPT View Post
    "Here is an analogy...a garden hose without a spray nozzle on it. If you let the water just run unrestricted out of the hose it flows out limply at a rather slow rate. However, if you take your finger and cover part of the opening, the water will spray out at a much much faster rate."

    when I read this I realised the author of the doc does not really understand flow rates at all......
    You only start to understand flow rates once you start to built performance engines.
    It is not what you buy its what you build.

  10. #29
    Join Date
    Apr 2009
    Location
    Bellville
    Age
    61
    Posts
    11,632
    Thanked: 727

    Default Re: Exhaust back pressure

    Quote Originally Posted by grips View Post
    You only start to understand flow rates once you start to built performance engines.
    ....................... or work in irrigation. The same basic principles apply, whether its gas or fluid.

  11. #30
    Join Date
    Nov 2007
    Location
    Kathu
    Age
    59
    Posts
    9,311
    Thanked: 2839

    Default Re: Exhaust back pressure

    Quote Originally Posted by ThysleRoux View Post
    ....................... or work in irrigation. The same basic principles apply, whether its gas or fluid.
    Dankie Thys party mense het nog nooit met iets gewerk nie.
    It is not what you buy its what you build.

  12. #31
    Join Date
    Mar 2008
    Location
    De Wildt
    Age
    57
    Posts
    37,450
    Thanked: 13611

    Default Re: Exhaust back pressure

    Quote Originally Posted by grips View Post
    That was the reason for split duration cams. When you ever come to Kathu I will give you a ride in one of my v8`s.

    I can put foot from 1500rpm in till 7000rpm. I do not want to start the old school vs new tech fight all over again.

    New tech is the future and that is not arguable.

    If I am allowed to compare a modern Lexus 1UZ vvti with one of my olds school v8`s. The old school v8 will kill it from 1500rpm to 7000. Yes I can slam 7000 with the aid the roller cams and balanced rotating assy. I know it is not fair to compare 5.0l vs 4.0l. But then the 4.0l have all that modern tech.

    What about a forum challenge. You can build a modern normal aspirated v8 of 5.0l (You can stroke a Lexus to 5.0l)and I will build and old school v8. Then we put them on a engine dyno. We restrict the budget for the built to R100 000.00
    and start out with stock engines.
    you misunderstand: I'm not knocking old school

    I'm pointing out why the manufacturers went with all the new tech

    it's how they manage to get a 1000cc 3-pot engine to be driveable in most conditions.
    2012 Jeep Sahara Unlimited 3.6 V6
    Percivamus

  13. #32
    Join Date
    Nov 2007
    Location
    Kathu
    Age
    59
    Posts
    9,311
    Thanked: 2839

    Default Re: Exhaust back pressure

    Quote Originally Posted by jelo View Post
    you misunderstand: I'm not knocking old school

    I'm pointing out why the manufacturers went with all the new tech

    it's how they manage to get a 1000cc 3-pot engine to be driveable in most conditions.
    Jelo thing is new tech is amazing. Yes engine design comes along way. Like you and Fluffy says new tech has smooth out the ride.

    I have build and re-build lots of engines, have seen high tech engines open saw the inner`s of older one`s even more.

    Before we lost the plot on this thread it is about the myth of flow and back pressure. As pointed out the article in the OP`s post is interesting and as pointed out not 100% accurate.

    The moral of the story is mods to the breathing system of an engine can only be determined with the aid of a proper flow bench. As you also pointed out there is not much room for improvement on a modern high tech engine.

    In person I believe the performance market with go faster goodies make use of the uninformed to promote their products.
    If a guy start to tell me about his 20kw increase on a normal aspirated engine by chip tuning and free flow systems..............
    well I say wow!!!!!!!!!!!!!!!!!
    Last edited by grips; 2016/09/27 at 12:00 PM.
    It is not what you buy its what you build.

  14. The Following User Says Thank You to grips For This Useful Post:


  15. #33
    Join Date
    Mar 2008
    Location
    De Wildt
    Age
    57
    Posts
    37,450
    Thanked: 13611

    Default Re: Exhaust back pressure

    Quote Originally Posted by grips View Post

    Before we lost the plot on this thread it is about the myth of flow and back pressure. As pointed out the article in the OP`s post is interesting and as pointed out not 100% accurate.

    The moral of the story is mods to the breathing system of an engine can only be determined with the aid of a proper flow bench. As you also pointed out there is not much room for improvement on a modern high tech engine.

    In person I believe the performance market with go faster goodies make use of the uninformed to promote their products.
    If a guy start to tell me about his 20kw increase on a normal aspirated engine by chip tuning and free flow systems..............
    well I say wow!!!!!!!!!!!!!!!!!
    agree on all points
    2012 Jeep Sahara Unlimited 3.6 V6
    Percivamus

  16. #34
    Join Date
    Feb 2015
    Location
    Cape Town / Seattle
    Age
    42
    Posts
    196
    Thanked: 28

    Default Re: Exhaust back pressure

    Quote Originally Posted by Fluffy View Post
    Exactly why they invented dual stage carburetors,

    First stage, small venturi, good engine response, smooth etc. Add second stage with larger venturi, max power at high revs and WOT.
    Yup - just like my Rochester Quadrajet in the US.. smaller ports def = more low down torque.. chevy guys in the states have commented feeling theye lost a bit of torque going from 2 1/4" to 2.5" -

    Its not actually a matter of back pressure but more of velocity, smaller tubes = more velocity up to a point. Most street cars need smaaler intake runners, smaller venturis, not over ported heads and not too big exhaust, collector and headers to really nail the sotp feeling -

    Most production cars can most certainly be improved, with all the epa regs these days alot of performance is usually left on the table.. im sure 90% of cars would totally benefit from a custom exhaust system - which makes me think of doing the same now actually haha
    Last edited by CamaroMan; 2016/11/02 at 07:05 PM.

  17. #35
    Join Date
    Dec 2008
    Location
    Richards Bay
    Age
    48
    Posts
    407
    Thanked: 28

    Default Re: Exhaust back pressure

    Just my 2c towards Grip. I agree with him 110%. Old school would do 500 000km with no breakdowns. Some of the new tech #### (excuse my french) cannot even make 100 000km and they are buggerd.

    New tech, new problems.
    Racing guys get 1000hp from a little 1994 Honda 4 cyl and they last. Not many of the new tech can do that. I had new tech, and gave up on them. Computers, cam belts etc dont last.

    Cheers
    Fazda

Page 2 of 2 FirstFirst 1 2

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
  •