This valve spring set has been developed to fit standard sized top caps, and cope with high rpm and high valve lifts without crushing of up to 0.570” without modifications, when fitted to a cylinder head that has standard or near standard valve spring heights. However, where possible, it is always advantageous to correct and match the valve spring heights (measured from the spring seat in the head to the underside of the spring retainer cap), as these will vary particularly where new valve seats are cut. The standard heights for pre-A+ heads are approximately 1.32” to 1.37” for small-bore types, 1.40” to 1.42” for large-bore types, and A+ heads 1.35” to 1.38” for small-bore types and 1.35”-1.37” for large-bore types. However, it must be stressed that these values are entirely dependant on the components used and machined condition of the head. Adjustments can be made by machining the spring seats, using shims of varying thickness or a mixture of both to achieve equalisation. Shims are available in 0.010”. 0.030” and 0.060” thickness.
At 1.40” fitted height, these springs will give a seat load of approximately 82.08-psi. 80-90- psi being preferred for super-sports road/track day type use, but dependant on valve lift. The aforementioned applies to valve lifts in the region of 0.400”. To calculate different loads for different height add/subtract 3.23-psi per 0.010” difference – for either seat or valve lift at the tip values. Set at the aforementioned seat pressure this will give a nominal at the valve pressure for the intended installation/use of approximately 200lb at 0.400” lift.
To calculate approximate seat load at 1.35” fitted length:
1.40”-1.35” = 0.050”
To calculate approximate load at the valve tip at any given valve lift - for example 0.500”:
0.500” divided by 0.010” = 50
Note: Valve lift value will obviously change with change in fitted height load, so make this calculation first. Rocker gear ratio will also alter over-all rate/load as seen by the cam/follower. To assess this, multiply valve tip load by actual rocker ratio – i.e. for 1.5 actual ratio with above 0.500” value – 1.5 x 243.58-psi = 365.37-psi.
It is ABSOLUTELY ESSENTIAL that the fitted height is NOT MORE than 1.42”. This will give a seat pressure of approximately 75-psi – the absolute minimum advised for fast road use, and where spring shuffle is to be avoided.