Street performance, restricted oval track, and marine performance upgrade. Mid-range to 6,500 RPM. Best for 383-434 cubic inch engines. Dart PRO1 23° 200cc Platinum series heads offer increased air flow at high valve lift for large displacement engines. Long wearing Bronze valve guides, screw-in studs, multi-angle intake seats with hardened, radiused exhaust seats are standard. Best of all, our precision cast ports produce outstanding airflow without time consuming porting.