Sonnax GM/Chevy 4T65E Sonnax Line Pressure Booster Kit Sonnax hydraulic line pressure booster kits contain stronger pressure regulator springs and large ratio boost valves designed to work together to provide progressive pressure increases as driving conditions become more demanding. Sonnax pressure regulator springs are approximately 10% stronger than OE and more conservative in impact than other aftermarket kit springs. Large ratio boost valves provide higher pressure incrementally and when it is needed the most. The combination of these springs and valves in a Sonnax kit gives you the best of both worlds: a modest pressure increase at the low end, with a high-end pressure that is equal to or greater than that of other aftermarket kit springs. Achieve shorter shifts and increased torque capacity without creating low-speed harshness Improved band and clutch holding capacity for increased durability Progressive pressure increase as driving conditions become more demanding All the benefits of increased line pressure without overloading the pump at idle Simple and affordable drop-in solution with no special tools or reaming required