Four-valve heads are certainly "cool", but comparing to modified 2-valve config, they exhibit a certain flaw - low speed torque is never impressive.
The key to making low speed torque is two-fold:
a) how much charge is trapped at valve closure and
b) how effectively the charge is burned."
Replacing 4V head charge "tumble" with the "swirl" motion presents itself as a key element of the successful (re)design.
To get details of this revolutionary PolyQuad head design, read this article:
Polyquad Article - MotorTech Magazine
If anyone wants a PQ head modified (be it for any multi-valve head), then Ultra Pro Machining in the USA http://www.ultrapromachining.net/About.html
(704-392-9955), who does so many cup car heads, or Austec Racing in the UK http://www.austec.co.uk/Cylinder-head-Modifications.asp
(01293 531080), are up to speed on this. DD required, DIY always encouraged, LOL.
WIPO Patent Application WO/2001/016469
The present invention seeks to provide, inter alia, further methods to generate swirl and reduce cross flow in spark ignition internal combustion engines having two inlet and two exhaust valves per cylinder head, without the use of additional moving parts. According to one aspect of the present invention there is provided an internal combustion engine comprising a cylinder head having formed therein first and second intake valves and one or more exhaust valves, the intake valves being disposed on one side of the cylinder head and the exhaust valve or valves being disposed on an opposite side of the cylinder head, characterized in that the engine is adapted so as to admit a greater flow of combustion charge through the first intake valve as compared to the second intake valve, the differential flow between the two intake valves imparting a swirl to the combustion charge as it enters the combustion chamber, the swirl direction generally corresponding to circumferential charge flow in the combustion chamber from the first intake valve, past the exhaust valve or valves and thence to the second intake valve.