When specifying springs we accommodate the possible maximum revs the engine may be using whilst minimising power loss through springs which may be too heavy. This is a careful balance. Too light and we could have valve float, too heavy and we could lose hard won power operating the valves.
Where required we have valves custom made to our specifications. We also use the very best 3rd party suppliers where they reach our standards for quality. Again we stand by our choice of 3rd party suppliers, they must have 100% integrity for engineering excellence.