well, you did ask for advice - and you didn't provide any information about what your build was. I assumed you were referring to a stock block max RPM. If you work the s*** out of the engine, the sky is the limit really. Most of us tend to top out at around 7200rpm anything else requires extreme work.
You have 3 enemies here. One is the head and manifolds - the stock equipment simply doesn't flow enough to take advantage of the extra RPM. You've already stated that you have solved this problem so thats fine.
Enemy number 2 is the bottom end. Specifically the fact that our engines are undersquare with short rods and a long stroke. this is actually not a terrible thing for a boosted engine as the resulting piston dwell at the top of the cycle is friendly to big boost applications due to a reduction in the motor's propensity to knock - more boost with more aggressive timing is possible. However this is the absolute enemy of RPM. The forces at play due to the poor rod ratio result in some rather wild piston acceleration numbers - and because of F = MA this puts a huge amount of stress on the engine. At north of 7400 rpm the engine will literally tear itself apart, forged rods or not. The heavier your rotating assembly the worse this becomes..and your rotating assembly will be heavier if you have a forged bottom end. Longer connecting rods and pistons with a wrist pin set higher to accommodate the longer rods will reduce the piston acceleration for the same piston speed (which is a function of stroke) and allow you to run a higher RPM but the engine will lose some of its resilience against knocking. The real question here is if you are boosting will you make more power by being able to run higher boost or will you make more with less boost and more RPM. I suspect the answer will be the former. If your heart is set on high RPM, install shield was running a rather extreme rod ratio for our motors (of about 1.6 or 1.7 i think?) with custom built billet aluminum rods to reduce the mass of the rotating assembly. To date, nobody has gotten close to his RPM numbers and if you talk to him the car was a bit of a headache to live with, with an insanely peaky power curve.
the 3rd enemy is fuel burn speed. It is possible at extreme RPM to have a piston speed which will literally outrun the flame front of the fuel which will act like a brick wall against raising the RPM further. You need to work out what the instantaneous speed of the piston at about 30 degrees after top of the stroke (most of the force exerted on the piston occurs within about 30 degrees after ignition of the fuel) - if within that 30 degrees your piston speed exceeds the burn speed of the fuel then fuel is your limiting factor. You can get around this with different fuels that burn faster, or longer rods to reduce the rate at which the pistons accelerate.
If you head over to the NA tech forum, race to 200hp thread (link in my sig) and search for stuff I wrote, theres a spreadsheet there which details a bunch of "stuff" specifically around getting lots of RPM out of the motor. Some of the maths may be off and I make no guarentees. Its really just a collection of best guesses and rules of thumb equations, but it should give you an idea of what you are up against. its also got some manifold design equations which might be helpful.
Good luck...post up your results once you're done.
