Looking for a bit of info

[COBOWTIE]

I am looking for so info from people that have over 650 rwhp cars. I value all opinions I am looking for more solid proven info. Having said that Here is what I am looking for.

First I figure I need a bigger Throttle body than the stock 90 mm KB website says they have a 110mm but not in prodution yet so they wont sell one to me. So any info on the S&B 102mm would be helpful. I have looked around here but I dont have lots of time to go through a bunch of threads.

Second Valve spring rates and what people are using.

Issue I am running into is I had my l99 with a KB 2.8 at 10psi making 575 rwhp 597 rwtq. I recently just installed a LSX 376 did nothing to the heads cam or springs just wnated for the forged and lower compression. Upped the boost to 18psi top side and the car still only made 570 and one 580. strangly enough the power never changed between 10 degrees of total timing and 18? Knock sensors are no going off.

So I am thinking that there is a airflow limitation. Yes I have checked and checked again fuel flow, pressure and injector plenty of fuel.

The car has an automatic I have done everything I know to disable any torque modulation no results with it on or off.

Having said that what does everyone think. There is a consensus that the valves are hanging open with that much boost but I thought I would see if anyone has any other ideas that are mechanically sound.