TCI boost Valves replace stock in all 700r4 & 200 4r applications. The boost valve increases clamping forces generated by higher line pressure. The 890-374301 is best suited for applications stock to 450hp. The 890-374401 is best for applications exceeding 450hp (best when used with the low rev. boost valve 890-374410), and the low rev. boost valve will bolster line pressure to allow you to get the added line pressure needed when making that BIG horsepower.