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Re: Head porting
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Posted by john williams [Email] (#1982) [Profile/Gallery] (more from john williams) on Sat, 13 Jan 2007 13:43:53 Share Post by Email
In Reply to: Head porting, John '96 Aero, Fri, 12 Jan 2007 15:11:42
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That is a tuff question to answer, the bang for the buck is not that high, maybe 20bhp for a ported/polished head, but if you have a larger turbo and tuned ecu, the gains may be more.

The thing that I noticed most on my port/polished head was the smooth power transistion from no boost to boost, it is much more of a smooth transition and the turbo comes on a little earlier.

I rebuilt my head about 6 months ago and spent around 18 hours porting and polishing the head. Get your machine shop to remove all the valves and such, then port match the exhaust and intake to the manifold gaskets. Next, get a good porting kit with multiple sanding drums and open up and polish the exhaust side to a mirror finish, you can also knife edge the dividers in the port, you will know what I mean when you look in the port. I left the shape of the intake alone and just smoothed the sharp edges up that disturb airflow. The last step took the longest, but may be responsible for most of the gains and that is the 16 valve bowls. You want to get in there and smooth out all the sharp edges from casting and flow it into the head. I opened them up some and then smoothed them out to flow nicely into the combustion chamber with nice smooth flow, no sharp edges!

Once you get the head intake and exhaust manifolds port matched and all the bowls flowed, put some old or bad valves in the combustion chamber and polish the combustion chamber only to a mirror finish, stay away from the edges as they help the head gasket seal. This will aid in carbon build up and keep detonation down and allow for more boost for a longer period of time :-) Remember to keep the intake side fairly ruff, like 80-120 grit for fuel atomization, but you want the exhaust side like a mirror, as smooth as you can get with polishing wheels. This too will aid in carbon build up and help with flow and more boost because of less detonation because of carbon build up...

I also had my machine shop do a 3angle valve grind to flow the valve seat area into the ported/polished bowls. He wanted me to install new valve springs for high rpm performance, but I declined for money reasons. We did replace all the valve stem seals though, they are cheap, maybe 1.50 each.


Its a lot of work and now I know why they want 1000-1500 bucks to do it professionaly. With my car it helped a lot with spool-up since I run a gt3071. I also ported/polished the turbo housings and exhaust manifold.
I was looking at my dyno sheets the other day and it looks like I spool-up around 300rpm later than my big T28 and for the extra 60whp and 40wtrq, it was worth it for me :-) Good Luck, John

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