Simply put, these are the best U20 production valves you can buy.  Top Quality USA CNC  production manufactured.  
 
 
Improved head design for better flow than obsolete Manley and  older Nissan OEM valves.  Swirl polished one-piece stainless valves with undercut stems.
 
Precision USA production machining surpasses the quality of all other U-20 Valves.  Far superior  in every way to overpriced=high profit  Manley valves from DatsunParts. 
 
Don't believe Dean's  webpage nonsense - his simply don't compare and he knows it....  
We never use  Chinese valve components!
 
This is a set of 8. 
 
Money back if you don't agree these are superb - better than Datsunparts!  We quarantee you'll be pleased!