What is Redline rpm of 13b 4 port with REPU rotors
 

What's the redline rpm for 13b 4 port with the heavy 11.5lb REPU rotors? Stock REPU internals with the exception of a streetport, 90psi oil, fancy Moroso oil pan. Aluminum RB flywheel if that matters.

Talking to myself here:
stock apex seals = 8,500rpm maximum
stock waterpump pulley + RB crank pulley = water caviates @ 7,200rpms. But it can take a quick burst up to higher revs occasionaly.
Rotating assembly not re-balanced or clearanced for high rpm usage, this would be a limiting factor.

So what's the redline?

And why would you want to go over 8,500 exactly? check the power curve before you get all bent over higher taching.

Want to see how far redline is *under* 8500rpms. Heavy rotors for REPU, remember....

If I wanna tach, my 12a built to live up to 10,4000rpms.

You pretty much got it. The stock iron seals don't "like" being over about 6200, so really 6200-8500 should be short-duration running, unless you don't mind the housings getting hammered.

Note stock redline was 6500.

The factory balance really isn't *that* much of an issue for the kind of running I think you plan on doing. It's not your limiting factor.