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I had a 2.1 head on the work bench all winter. I gathered info from the internet, ChrisX, Kooch and Steve Y. and went at it with a dremel tool. This was my first attempt at modifying a head so it doesn't require a lot of expertise. If you are willing to take the time all it takes is a dremel tool and some cutting fluid. From my memory I did the following:
Intake and exhaust ports;
*Carved out the intake and exhaust port about 1/16.
*Polished the exhaust but not the intake.
*Gasket matched the intake ports but not the exhaust. (The step down on the exhaust is supposed to promote flow.)
Compression Chamber;
*Unshrouded all the valves. Very important--especially the intake valves. Anything closer than 3/16 should be trimmed back. You can tape a gasket to the head and etch the top with a sharp point to know your limits. Be very aggressive with this and your head will flow air quite nicely. * Carved out the head completely to the valve seat level and created a hemispheric bowl. You can do this and slap it on to a stock gasket (.050) and you will be at roughly 8.5:1. My volume was 48.6 cc on all the chambers after taking out a lot of material. I went with a .070 copper gasket because me head was at the short end of spec for height. The .070 raised it up to get the timing correct. Using plexiglass, water, scale, bike grease to seal the plexiglass to the head and tubing to volume match each compression chamber. I don't have the formula with me now but I ended up with a compression ratio of 8.1:1. *Into the shop for a good valve job. I love the results. Today I drove 300 miles in +25 C. with consistent boosts to 16 psi with no apc cutbacks. Acceleration (torque) feels stronger and detonation is non--exsistent. Don't worry about running lower compression ratio. I don't believe that it adds to turbo lag from my experience. Of course this is on a car with an external wastegate, viggen fmic and modified apc. Hope that helps.
posted by 64.12.101...
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