Learned something today that some of will most likely know others may not.

Been Monday morning quarterbacking my engine now that it’s finished and running. Been concerned that I don’t have enough valve spring for my camshaft. Manufacturers give a range for closed and open valve spring pressure depending on the type of cam you have. So did a little research and I learned that you can’t take the open pressure for face value. You need to calculate open pressure by multiplying the spring rate by the valve lift then adding the seat pressure.

So, I have a set of Howard valve springs that have the following specs:

Closed Pressure:
 135 @ 1.750
Open Pressure:
 285 @ 1.250
Rate:
 300
Max Lift:
 .625

However, the open pressure for these springs is based on a valve lift of .500 - .500x300+135= 285lbs (valve lift x spring rate + closed pressure)

If your cam had .600 lift the open pressure actually increases to 315lbs. Obviously higher than the 285lbs advertised.

So comparing this to another one of their valve springs:

Closed Pressure:
 145 @ 1.750
Open Pressure:
 315 @ 1.150
Rate:
 283
Max Lift:
 .665

With just looking at the open and close pressures, one would assume this is a stiffer spring; however, the spring rate is only 283.

So if we do the same formula .500x283+145 = the springs open pressure is 286.5lbs. Well below the 315 advertised rate.

You would need .600 lift to get to the advertised spring rate.

So moral of story, look at valve spring rate, camshaft lift and closed pressure to determine your open pressure.


https://calculator.academy/valve-spr...te-calculator/