Mk1 Focus RS - Zetec Blacktop + ST170 AREA6 Up-rated Valve Spring Set
Turbocharged and performance engines require more of a valve spring. The pressure within the intake valve is Boost pressure, and this acts upon the valve head, significantly reducing the valves ‘seat pressure’ as the boost is trying to push the valve open. The same impact occurs on the exhaust valve head. Whilst Ford provided the Focus RS with a mildly uprated spring set to suit the turbocharged application, these become ineffective after 20psi boost, and will allow misfires once RPM’s exceed 5500rpm
The Area-Six valve springs are a direct fit to all black-top engines, including the ST170. They provide an additional 25-35lbs extra seating pressure over factory Focus RS valve springs, whilst allowing an additional 3.9mm of valve lift for high lift naturally aspirated applications.