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I'm going to soon be doing a DIY port and polish on a good used 86 8V n/a head with low mileage to replace my existing 8V turbo head with high mileage and considerable corrosion damage. The sa-motorsports.com website was very helpful with the basics of this mod. I'm not looking for huge performance gains by doing this mod. Rather, I'm just doing it for the practical replacement of a bad head, the experience, some fun (yes, fun) as well as the extra performance edge gain to go along with the other performance and maintenance edge gains I've so far done (IC install, cool air induction, two below bumper oil coolers - one for the turbo oil feed line, thorough intake system vac/boost leak overhaul, distrib vac advance unit mod for ping killing added retard during boost, boost controlled warm-up/fuel pressure regulator) to this car.
What I'm interested in knowing from those of you who have had this done to your car is what you've noticed. Any DIY experiences? Those who've had it done by a shop, did you see the extent of the metal removed - a before and after comparison? I'm particularly interested in anything relative to the internal surface edge of the valve seats on the intake side. On my 8V there's a considerable lip along the bottom (within the valve bowl region before the combustion chamber) surface of the valve seat. It's a natural obstruction in terms of air flow going into the chamber. Porting philosophy says to remove such edges by smoothing and tapering if at all possible. If done properly, this would make sense and in no way effects the all important valve seat surface. In theory.
Then there's the exhaust side porting. Again relative to an 8V T design, anyone having done a port job - is it a good idea to enlarge the exhaust ports? Reason I ask is because the website listed above talks about a natural surface dam "step" from small to large when going from the head to the exhaust manifold. That step is designed to reduce back flow pressure. So why enlarge the exhaust side port exits at all if that's the case? Perhaps polishing the interior surfaces of the head exhaust ports is all that's necessary. Or if enlarging the exhaust ports, also enlarge the manifold ports so as to acquire that step. Something tells me that incorrectly porting the exhaust side of the head on these cars could lead to unexpected boost related issues, like a dip or spike in the boost curve. But then again - more air in and out is good!
Comments, insights and expert advice are welcome!
posted by 198.81.18...
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