Valve Spring Pressure & Coil Bind Check
Open pressure from seat pressure and spring rate, and how close the spring comes to stacking solid at peak lift.
| Open pressure at max lift | 322.5 | lb |
| Seat pressure | 130.0 | lb |
| Spring height at max lift | 1.250 | in |
| Clearance to coil bind | 0.150 | in |
| Maximum lift with 0.060" left | 0.640 | in |
- open pressure = seat pressure + (spring rate × valve lift)
- clearance to bind = installed height − valve lift − coil bind height
- Most builders want 0.060" or more remaining at peak lift.
When you need it
After any cam change, whenever you increase lift with a rocker swap, and as a periodic check on springs that have been in service.
Coil bind is not the only clearance
Sixty thou of remaining travel at maximum lift is the usual minimum before coil bind. A spring that stacks solid takes the retainer, the pushrod, the rocker and sometimes the valve with it.
This calculator covers bind. You still need to check retainer-to-seal and retainer-to-guide-boss clearance, which wants around the same sixty thou, and piston-to-valve clearance separately. A spring that clears bind comfortably can still crush a valve seal.
Springs fade
Seat pressure drops with heat and cycles, and it drops fastest in the first few hours. A spring that has lost fifteen or twenty percent of its seat pressure will float the valves well below the RPM it used to hold.
Check pressure on a tester at every valve job rather than trusting the part number. If you are chasing a high-RPM misfire that is not ignition, tired springs are near the top of the list.