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ddgonzal wrote:
naukkis, I hear what you're saying about using these heads in a high-compression engine ... but not sure why these wouldn't make a good low/mid compression engine. Some of us would prefer a 8.5/9.0:1 engine for the street rather than racing. At this compression using these "anti-smog" heads, our least expensive gasoline doesn't ping (use a 180 degree thermostat).
Yeah, it won't ping but either it won't produce power and also has bad fuel economy.
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Can you elaborate on why the open chamber is bad?
Because it's ruined head design just for emissions.
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The valves in all A14 heads are inclined, making it a wedge-head (?) except for the large volume below the valves, which as you point out can be milled off. It's still open chamber though, if I understand correctly open chamber means the area around the valves is more flat and "open". The open-chamber design I thought was good for airflow, and using popup pistons to raise compression was superior to closed chamber.
No, closed chamber just means that chamber is closed eg some part of chamber is at same level as head sealing and upcoming piston closes the chamber so it becomes smaller rapidly. That squish area is the reason for wedge-head and when tuning you want to make piston to come as close as possible to those squish-areas( and make those squish-areas as large as possible without sacrifacing flow). That open-chamber head makes just opposite, real anti-tuning to engine and that so stupid that you have to wonder why Nissan ever made those.
Here's some link.
http://www.chevyhiperformance.com/techarticles/94138/