Where to port next..

The problem with this port are many. For one, people just look at it and think.. that is a really bad push rod pinch for a 4v port..then find out it is not a 4v head. While the port is definitely odd it does seem to work.


Take for instance the BMW N52B25 inline 6 engine produced from 2004 to 2011 . It has all the modern trinkets, 4 valves per cylinder + VANOS and being a BMW is well engineered. Being an inline 6 it’s silky smooth too.

It produces 174 BHP/130KW from 2497cc or about 69 BHP/liter at 5800 rpm. and 92NM/liter torque from 3.5k to 5k.

Very similar figures are achievable from the little A-series with good mileage and good emissions . Had they bothered to rework the tooling so that the head was cast as it is ported (not exactly rocket science) it would have done so directly out of the box.

Well enough about why you have to just live with the fact that it looks odd but still works, and labour on to get it to work a bit better ; ) Even if standard rules do no apply.. if you look at the entire port as one piece.

I heard about flowballs.. do a google, it will reveal a hilarious video with a guy in a white coat.. As a professional white coat bearer I get acute multiple allegries, but that is mainly my personal problem. The basic premise is fine.. stick something in a port.. if it does not care.. there is no sense starting there. If it does not like it , you have found a part where air is flowing and that is a reasonable place to start removing metal.

Two thing I noticed.. the siamese section can be a bit larger I think. If i reduce the cross section only slightly (a 2mm layer of plasticine on the port floor) flow suffers quite badly. So the roof will be a bit reworked. And the upper corner after the pushrod pinch is very active. Downside is that it is very hard to reach.


the arrow indicicates the port where adding an obstruction, severely affect flow.
(done at 8mm lift)











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3 thoughts on “Where to port next..

  1. stumbled on your stuff! its very good! havnt read it all but i like it. best wishes peter in manchester (with a gtm rossa 1310cc single hif44 and 6.5 inch ram special pipe) find my rantings on gtmowners forum . .
    PS. it does seem that : 1 get more flow with a 30 degree backcut to the valve. 2. get more hi lift flow by removing the valve guide boss completely 3. determine where your peak torque is by varying the ram pipe length. obviously there is more to it than this but its good to have a three bullet point summary . . . 🙂

  2. ive just looked at the “where to port next” from september. really sorry if this is wrong or already covered elsewhere. i have the the vizard book but bought all the car tuning magazines in the 1990s. some interesting things were covered in the magazines but no-where else . what turned out to be important was what sort of inlet manifold you were using eg a 7 inch long weber manifold put the air into the ports in a different place than a good single su manifold. im pretty sure i remember reading that the single su manifold put the air in the bottom of the port. i would be REALLY interested to see if the restriction you identify is the same with 1 long weber manifold 2 no manifold just platicine radius and 3 minispares inlet manifold (or similar)

    • mowog says:

      thanks for the input

      It is interesting but I do not have a weber manifold to use. Testing it is quite involved as you have to build up a restiction using something like bondo (you have to remove it afterwards) because plasticine will most definitely not stay put at 28 inch depression !

      Personally i’m not s big fan of the weber noise ( Rare I know..).
      The differences between a manifold off and just a radius entry have I have tested a while back. There is quite a bit of flow loss. If this relates to power loss as well remains to be seen as AFAIKT the resonance behaviour of the whole system is very important as well (lets face it is port is a disaster in term of sensible and simple design).. but it just sounds so ..plucky.

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