Engine Porting

  1. Saxperience Forum Bum Joined: Dec 2008 Pontefract Posts: 4007 2010 E92 320i MSport
    #1
    Dont worry, i'm not about to go hunting in the shed for my Dremel!

    I've just been reading up on the subject and something has become quite apparent to me. When I fitted my Janspeed manifold the holes into the pipe work were round, whereas the port exits on the head are a rounded square shape, now from what I understand this is not a good thing as the holes on the janspeed manifold are narrower than the head ones, but slightly higher.

    1.) Why would Janspeed design it like this?
    2.) What would be the best bits to remove when port matching?
  2. Saxperience Forum Bum Joined: Dec 2008 Pontefract Posts: 4007 2010 E92 320i MSport
    #2
    Anybody got any clues yet?
  3. Saxperience Post Whore Joined: Mar 2007 Yorkshire Posts: 5415 Saxo
    #3
    1.) Mass produced, dont care.
    2.) You'd need to ask someone with the equipment to flow test heads, then they can tell you if the oval going to a circle to match the mani would be bad or good.

    I have a GMC, Ricky-P matched this up for me without any probs as the holes were oval - maybe a bit cheaper to sell on the janspeed and get a GMC. But the GMCs a 4-1 so it shifts power upwards.

    Ive been told time and time again that the flow of gas is a very very complicated subject to be treated with respect, so its something i ask the experts on.
  4. Saxperience Forum Bum Joined: Dec 2008 Pontefract Posts: 4007 2010 E92 320i MSport
    #4
    Cheers Ste, i've just bloody fitted the manifold too, it wasnt something I thought about until after. Could have sold it brand new.

    BTW, I think your car looks fucking mint.
  5. Infrequent Poster Joined: Oct 2008 Posts: 152 MK2 vtr saxo in silver
    #5
    whether you alter the shape of the head or the shape of the manifold would depens on the CSA of the port (cross sectional area) you dont want a joint with say 150mm*2 of csa and a pipe with 125mm*2 csa (i just made figures up by the way.)
  6. Saxperience Addict Joined: Jul 2005 Solihull / Bournemouth Posts: 14233 2015 Lapiz Blue Golf R
    #6
    From Reading a few tuning books they say that by having the manifold tube slightly bigger, with a step from exhaust port to manifold port adds bhp - something to do with helping scavange the exhaust gases.

    I'll dig it out Sunday evening and post here about it.
  7. Saxperience Post Whore Joined: Mar 2007 Yorkshire Posts: 5415 Saxo
    #7
    Quote:
    Originally Posted by raunchz View Post
    From Reading a few tuning books they say that by having the manifold tube slightly bigger, with a step from exhaust port to manifold port adds bhp - something to do with helping scavange the exhaust gases.

    I'll dig it out Sunday evening and post here about it.
    On my GMC the end plate that holds the manifold to the engine and the primraies that are welded to it - they are slightly bigger than the end plate. So, would having the exhaust matched to the head and the slight stagger between the manifolds plate and pipes give the desired gain like it says in the book.

    Or would having two staggers, the head and the manifolds plate be better?.

    Think i might nip to borders and get some books