sitnlo62 wrote:
The installed height, length of a valve spring should be determined once you have decided on the poundage you want the valve to be at when it is on the seat.
For example if you want 85 pounds on the seat you have to determine at what length the spring produces 85 pounds.
Keeping in mind that when the valve is at full lift the pressure will be a lot higher and it becomes a bit of a juggling act to determine the comparison between on the seat pressures and full lift pressures.
It is like having to rob peter to pay paul.
For example if you set it up with 85pounds on the seat it may only produce 175 pounds at full lift which may not be enough so it may be necessary to set it at 95 on the seat which will increase the pressure at full lift. (PLEASE NOTE THESE FIGURES ARE FOR EXPLANATION ONLY)
The Cam shaft designer should be able to tell you what pressures work best with his particular cam.
To achieve these lengths and measurements a Valve Spring tester must be used and accurate measurements must be taken of the spring lengths for the pressure readings.
This is a fairly long and drawn out process and can take some time.
Personally I never rely on what pressures a spring manufacturer claims of their springs, simply because they are never totally accurate.
One word of advice on spring pressures on mini engines.
Never use more pressure than is necessary, it leads to premature wear of valve train components and Robs horsepower.
Dave
Yep, I found out the expensive way that too much Spring pressure leads to broken valve. If using hi compression springs use race quality valves at around $45 per valve, gets expensive real quick.
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