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Head porting..what to avoid.. 120-130

posted by  amazon69 on  Sat May 24 10:26 CST 2008
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last visit: Tue Aug 21 14:46 CST 2012
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Hello all,
I've got a big valve head (standard,44mm inlet etc) on the bench, from an early 70's 200 series,non injection, and I want to clean it up, polish the ports, improve the flow etc..but I vaguely remember reading that grinding out these heads has to be carefully done so as not to actually have a detrimental effect on performance..
What do I need to avoid in there, and what should I aim for? I am not going to go mad, just smooth out a bit, sort the rough castings etc..I am as much interested in smoothness and economy as power. I have done it on a few heads before, mainly minis, and once on a b20a head, and there was always an improvement..what's so different about these volvo heads that I must avoid?
Thanks all for your help..always appreciated.
best,
Dave White








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    Head porting..what to avoid.. 120-130

    posted by  someone claiming to be B20Paul. on  Sun May 25 17:44 CST 2008 [RELATED]

    Click here for some fuzzy pics.

    This exhaust port flows 133cfm@28"H20 with 35mm B20E valves. This is as much as a standard B18 inlet.

    Take no metal away from the LSR between the seat & guide. Take metal away on the roof the other (outside) of the guide. Use as large as possible radius on the SSR.

    Get hardened (stelite) seats installed before you start porting, standard angles are good, I'd try a 15 degree cut on the exhaust only: 15/30/45/60

    Just 3 angles on the inlet with a 30 degree top cut on the valve.







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    Head porting..what to avoid.. 120-130

    posted by  122_Canadian on  Sun May 25 06:32 CST 2008
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    last visit: Tue Oct 20 07:51 CST 2009
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    Dave,

    E-mail me off list if you'd like some photo's. One of our local volvo guys had a vast collection photos of B20 heads that had been ported. Most are Swedish and range from mild to wild. Rhys's description, by the way, is a spot on description of my B20 VPD head.

    Craig

    craig_coburn at hotmail dot com








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    Head porting..what to avoid.. 120-130

    posted by  Rhys on  Sat May 24 13:53 CST 2008
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    last visit: Tue Nov 20 10:22 CST 2012
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    There is nothing different. The best, most effective route is to blend the valve pockets (bowls) to achieve a smooth transition from the "as cast" port. Do a rough three-angle valve grind first, and then blend the bowl into the lower 60 degree cut. Remove any other casting flash, and don't be concerned with hogging out the runners. Just get a good smooth profile from the square port to the round valve seat area. I also back-cut the intake valves - I move the intake valve seat contact point higher on the valve face, and then put a 30 degree back cut on the valve to ease the transition from the neck to the face.
    This way you achieve 80% of the improvement for 20% of the time.








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      Head porting..what to avoid.. 120-130

      posted by  amazon69 on  Sun May 25 02:06 CST 2008
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      last visit: Tue Aug 21 14:46 CST 2012
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      Thanks Rhys, all sounds simple enough. Why is it then that I have read that it is possible to do more
      harm than good? Just like it is on any head, or something volvo specific? It all looks pretty standard in there to me..

      atb,
      Dave








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        Head porting..what to avoid.. 120-130

        posted by  Rhys on  Sun May 25 09:34 CST 2008
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        last visit: Tue Nov 20 10:22 CST 2012
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        It's not Volvo specific to my knowledge. If there is a spot to stay away from it is the "short side radius", which is the floor of the port on both intake and exhaust. That profile should be blended at the valve seat, but the radius must not be flattened at all. That may be the area that gives rise to the horrible predictions of lower performance.







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