These cams, especially the 5R, were designed to the outer limits of the valvetrain geometry. On this family of Mitsubishi head designs there is a limitation of how much valve lift we can achieve while maintaining good rocker arm to valve tip contact and stability.

Having proper valve stem height is REQUIRED in order to use the 5R cam. This is not an option.

If you have an OEM head that you KNOW FOR A FACT has never had a valve grind, does not have aftermarket valves, you are OK. If you have had a valve grind, or have aftermarket valves, checking stem height and correcting to factory spec is REQUIRED.

Being slightly higher (up to .010") than spec is generally OK, the high lift designs favor a stem height slightly higher over one that is slightly lower, but if the stem heights are too high HLA travel and proper operation is seriously compromised.

When the roller is on the cams base circle (valve closed) we recommend the HLA can be further compressed a MINIMUM of .060". This allows for the thermal growth in the length of the valve, especially the exhaust valve. If this clearance is too small, lowering the valve stem height is necessary by grinding off a small amount of the stem tip. You cannot just go to town on the stems- there is a limit to how much you can grind off before the rocker to retainer clearance becomes a problem, we recommend NO MORE than .010" come off in most cases.

If the stem height is too low, the rocker arm to stem contact goes off center at full lift, and rapid stem/rocker and valve guide wear occurs, if not total high RPM carnage.

The current production rocker arm has a slightly longer pad and is recommended.

If your rocker arms are galled or worn flat in the center of the valve contact pad, throw them away and get new ones. Most people NEVER check these. Do so.

If your valve guides have been replaced, you need to make sure the guide height has not been increased over factory spec, otherwise valve seal damage or guide to retainer contact can occur.

It is amazing how many otherwise reputable machine shops, with high dollar Serdi, Sunnen, Newen valve seat cutting machines CANNOT GET THESE SIMPLE SPECIFICATIONS CORRECT. Do not trust them, make them provide you with measurements of stem height and valve guide height.

For very high RPM applications we recommend using the early DSM style HLA's (they have a smaller diameter plunger) and reducing oil pressure to the HLA oil galley by using the early JDM oil regulator or a restricted orifice in the oil distribution block. These two items reduce HLA pump up effects.

Notes about EVO valvetrains-

Due to the very tall aluminum retainers used by the factory, valve lift with the factory retainers is limited to ~.445" max otherwise the valve seal will be damaged by contact with the bottom of the retainer. If you have had valve guides replaced, be sure they were installed to the correct protrusion specification. 119 ( EVO8) and 145 (EVO9) series EXHAUST cams are the same, only the intakes vary due to the special core required for the MIVEC system.

TECH TIP: Spring upgrade required, will not work with factory retainers. Must check for coil bind. 11K RPM capable with good springs. Further increase in upper RPM power. Intended for use with 65+ lb/min turbos. Works well with header equipped engines. Not intended for use with factory pistons. While most aftermarket pistons allow for adequate piston to valve clearance, checking clearance is highly recommended, especially with oversize valves. Choppy idle, not recommended for factory ECU's or any ECU that you cannot disable O2 feedback at idle. Recommend increasing idle RPM to ~1200RPM. 

Fits: Mitsubishi Lancer Evolution VIII 2003-2005