Ramp speed....
Valve "lash" is a recommended setting of the cam manufacturer based on ramp speed... Some cams are slower than others and require less clearance to maintain the designed duration of the camshaft... Others are fast, and require more. An old school idea says that loose lash gives you more bottom end, and tighter lash gives you top end, and additional RPMs. (not a lot, but some).... A mere .002 tighter MAY give you 200 RPM up top by increasing the duration of the "valve event". The lift isn't changed enough to matter.... The .018-.028 settings mentioned are certainly close enough to run with just about any solid grind, and from there some close monitoring and a little experimentation will allow you dial it right in to your application..... If it's a monster down low and noses over up top, try tightening in .002 increments until you balance out your performance for the best of both worlds.... I set valves cold, and if I need to check hot I'm only looking for consistency throughout the valve train...Which will also tell me where, (.xxx), my cold setting is when hot.... IMO, the best thing you can do for a solid cam application is a quality stud girdle to keep things where YOU put them.....
Ray
)eek
