Originally posted by BustedLX
The reason an engines red line is set at a certian value is because that is the limit the engine will safely and reliably operate.
When you over rev an engine the engine can spin itself, run away, etc. there are many different terms but basicly it's when the interia of the moving parts acutally carries the engine past it's own power.
The reason the springs are changed first is because they are the first to fail. At high RPM they can drag and at that speed the pistons can litterly hit the valves. So buy putting higher tension springs the valves will seat faster, getting them out of the way so the engine can rev higher.
There is always a limit but I have seen a completely built engine built by JUN that reved to 13K. Pretty Impressive.
Good explaination bro. Couldn't have said it better myself.