User Tag List

+ Reply to Thread
Results 1 to 18 of 18

Thread: Twin weber manifolds

  1. #1
    Bodger

    Join Date
    Jul 2015
    Location
    shropshire
    Posts
    168
    Thanks
    26
    Thanked 6 Times in 4 Posts

    Twin weber manifolds

    Hi are there any advantages between short or long twin side draught inlet manifolds?
    Cheers

  2. #2
    Racer

    Join Date
    Mar 2010
    Location
    Edinburgh
    Age
    41
    Posts
    3,504
    Thanks
    53
    Thanked 220 Times in 216 Posts

    Re: Twin weber manifolds

    Longer the better, usually inner wing clearance is what limits things

  3. #3
    Bodger

    Join Date
    Jul 2015
    Location
    shropshire
    Posts
    168
    Thanks
    26
    Thanked 6 Times in 4 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by Erikmex View Post
    Longer the better, usually inner wing clearance is what limits things
    Thanks m8 was not sure if people had short because of like you said iner wing clearance in mk 2 escort.why is longer better? Cheers

  4. #4
    Racer

    Join Date
    May 2012
    Location
    Camberley, Surrey
    Posts
    2,220
    Thanks
    3
    Thanked 196 Times in 196 Posts

    Re: Twin weber manifolds

    Longer inlet runners generally improve torque - sometimes significantly in injected set-ups!

  5. #5
    Racer

    Join Date
    Mar 2010
    Location
    Edinburgh
    Age
    41
    Posts
    3,504
    Thanks
    53
    Thanked 220 Times in 216 Posts

    Re: Twin weber manifolds

    It’s all to do with pressure waves, if you imagine the inlet flow on an induction stroke flowing through an open inlet valve, when that valve closes the flow through the runner dead heads sending a pressure wave in the opposite direction, when the cylinder then comes onto its next induction stroke that pressure wave inside the runner has more energy and a higher gas speed in a longer inlet tract vs a shorter , so when the valve opens again it assists cylinder filling, there’s more to it than that but in short.

  6. #6
    Bodger

    Join Date
    Jul 2015
    Location
    shropshire
    Posts
    168
    Thanks
    26
    Thanked 6 Times in 4 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by Erikmex View Post
    Itís all to do with pressure waves, if you imagine the inlet flow on an induction stroke flowing through an open inlet valve, when that valve closes the flow through the runner dead heads sending a pressure wave in the opposite direction, when the cylinder then comes onto its next induction stroke that pressure wave inside the runner has more energy and a higher gas speed in a longer inlet tract vs a shorter , so when the valve opens again it assists cylinder filling, thereís more to it than that but in short.
    Thanks guys v informative

  7. #7
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    52
    Posts
    23,724
    Thanks
    233
    Thanked 1,907 Times in 1,786 Posts

    Re: Twin weber manifolds

    there is also a ram air effect, air has interia like everything else, so once you have a long column of air moving it doesnt want to stop so tends to carry on filling the cylinder even when the engine is actually pushing the air back out again or even sometimes a slight supercharging effect

  8. #8
    Bodger

    Join Date
    Jul 2015
    Location
    shropshire
    Posts
    168
    Thanks
    26
    Thanked 6 Times in 4 Posts

    Re: Twin weber manifolds

    Does that mean longer trumpets are better as well

  9. #9
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    52
    Posts
    23,724
    Thanks
    233
    Thanked 1,907 Times in 1,786 Posts

    Re: Twin weber manifolds

    yes, as far as the engine is concerned it just sees length of inlet, long manifold short trumpet, short trumpet long manifold will perform the same, there is always the odd exception, but in the vast majority of cases long is good, and on older 2 valve per cylinder engines ive never seen an instance where you can go too long and still fit the induction system to the car. i say that as i did once try some 1 metre long trumpets they were too long for the very top of the rev range, but the midrange was something else altogether

  10. #10
    Racer

    Join Date
    May 2012
    Location
    Camberley, Surrey
    Posts
    2,220
    Thanks
    3
    Thanked 196 Times in 196 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by Graham View Post
    i did once try some 1 metre long trumpets they were too long for the very top of the rev range, but the midrange was something else altogether
    That I would have liked to see LOL!

  11. #11
    Spanner Monkey

    Join Date
    Jan 2016
    Location
    Hull
    Posts
    221
    Thanks
    2
    Thanked 17 Times in 17 Posts

    Re: Twin weber manifolds

    What would a 90 degree bend in the trumpet effect have to get more length ?

  12. #12
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    52
    Posts
    23,724
    Thanks
    233
    Thanked 1,907 Times in 1,786 Posts

    Re: Twin weber manifolds

    Problem with a 90 bend is air doesnt like going round corners, so you'd probably be worse off

  13. The Following User Says Thank You to Graham For This Useful Post:


  14. #13
    Bodger

    Join Date
    Jul 2015
    Location
    shropshire
    Posts
    168
    Thanks
    26
    Thanked 6 Times in 4 Posts

    Re: Twin weber manifolds

    So the longer trumpet is benefitial so what about longer filters does this have same effect

  15. #14
    Racer

    Join Date
    Mar 2010
    Location
    Edinburgh
    Age
    41
    Posts
    3,504
    Thanks
    53
    Thanked 220 Times in 216 Posts

    Re: Twin weber manifolds

    I learned the lesson when I was 8 on my first bike, a 2Stroke 50cc Italjet. When we got it it was flat as a pancake until high revs. My dad made around 5 different length trumpets for various conditions ie. deep mud, hardpack etc. The smaller dia longer ones had best low end to mid. And the shorter larger dia ones have more top end
    Last edited by Erikmex; 05-10-2018 at 18:39.

  16. #15
    Racer

    Join Date
    Mar 2010
    Location
    Edinburgh
    Age
    41
    Posts
    3,504
    Thanks
    53
    Thanked 220 Times in 216 Posts

    Re: Twin weber manifolds

    No because filter are open, they don’t increase gas speed

  17. #16
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    52
    Posts
    23,724
    Thanks
    233
    Thanked 1,907 Times in 1,786 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by Painter an View Post
    So the longer trumpet is benefitial so what about longer filters does this have same effect
    no, because the filter doesnt form part of the actual inlet tract

  18. #17
    Racer

    Join Date
    May 2012
    Location
    Camberley, Surrey
    Posts
    2,220
    Thanks
    3
    Thanked 196 Times in 196 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by Graham View Post
    Problem with a 90 bend is air doesnt like going round corners, so you'd probably be worse off
    Depends on how you bend them - VW have some interesting,curved inlet tracts and plenums - not sharp 90's but long sweeping 180 turns that I believe are over 300mm long

  19. #18
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    52
    Posts
    23,724
    Thanks
    233
    Thanked 1,907 Times in 1,786 Posts

    Re: Twin weber manifolds

    Quote Originally Posted by katana View Post
    Depends on how you bend them - VW have some interesting,curved inlet tracts and plenums - not sharp 90's but long sweeping 180 turns that I believe are over 300mm long
    i agree, but your not going to get anything like that fitted to and x/f in an escort

+ Reply to Thread

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