Inside the 455 Super Duty
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To retain constant port cross-sectional area, any point seen as a restriction on standard heads was removed on the SD-455 head for maximum port flow and velocity. Most notably, the port at the pushrod bulge was widened far enough that the guide broke into the port wall and a tube was used to prevent leaks. A close look at the adjacent port roof reveals the valve cover bolt hole that has broken into the port roof. View Related Article
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