OVERSIZE VALVES
A bit more prodding into evo compatibility on my part has turned up evo valve similaritys
Evo Inlet Valve
- Diameter = 34mm
-Length = 110mm
-Stem diameter = 6.6mm
Evo Exhaust Valve
-Diameter = 30.5mm
-Length = 110mm
-Stem diameter = 6.6mm
followed by 6A13TT valve measurements
6A13TT Inlet Valve
- Diameter = 33mm
-Length = 104.8mm
-Stem diameter = 6mm
6A13TT Exhaust Valve
-Diameter = 28.2mm
-Length = 104.8mm
-Stem diameter = 6mm
This Possibly means 6A13TT heads can take evo or aftermarket evo titanium or billet valves with a re work of the valve seat and chainging the valve guides to accept the bigger valve stem of the 4G63T valves.
the inlet evo valve fits easily within the standard 6A13TT valve seat so only a regrind of the valve seat and valve guides would be needed on the inlet side. however on the exhaust side it is a tighter fit but I think it is possible in the limits of the stock valve seat. I Still have to take the head into a cylinder head specalist to get their opinion on the matter.
If We can use evo valve guides with evo valves. that means we can use aftermarket evo dual valve springs. dual valve springs require their own special retainer and due to our engines having the 4G93T valve stem size, we cannot use 4G63T retainers on our standard valves. Main reason for pushing to use evo stuff is easy aftermarket support to easily make the heads safer to rev higher without valve float aswell as making the heads breath better throughout the rev range, helping with Volumetric Efficency therefore more power
there is also aproxx 5mm difference in length between 4G63T and 6A13TT valves, however this should be taken up by the lash adjuster, especially if used in conjunction with a cam regrind as the cam regrind makes the base circle of the cam lobe smaller to get larger lift from the cam. see here ----http://www.clubvr4.com/forum/showthread.php?60575-EOI-Aftermarket-cam-grinds-and-Valve-spring-group-buy&p=675147#post675147
Pictures of valves compared next to eachother are featured in the above linked thread.