[SCOBRAC]

Redlines are different for different reasons. Most redlines are determined by the practical application of physics. That, is if you go to fast for too far, things break. There is however a point most engines just don't make any more power no matter how fast they turn.

The question of how far how fast must be determined by you and your engine builder. I say by you because you spec'd the parts he installed and I say by him because he's got to warranty the thing if it breaks.

Most performance engines will rev well past the point we may usefully drive them. A well built small block (stroker or otherwise) may have a mechanical limit of over 8,000 rpm. It may only make useful power to 6,200 rpm depending on camshaft selection, duration, lifter choice etc.

You should know where this point is and know going past it is useless. If the point is sufficiently high enough to begin worrying about mechanical failure you may want to find it once (typically during dyno tuning) and set a livable value (say 80-85% of that number) and call that redline.

I know one 1966 427 Cobra owner that has the word "think" in Dymo label stuck to his tach. I know another with red paint marks on the glass of his. Both are examples of self imposed redline well below the mechanical ability of their machines.

If you must have a number and are not going to dyno tune the engine take it out after it is run in and wind it up in 3rd. Note the rpm where power begins to fall off. Take a couple hundred rpm off that and call it redline (this allows for the amount of time it took your brain to realize power was falling off).

If you get to a point power has not fallen off but you decide enough is too much call that redline. 80% of 8,000 is 6400 rpm