In my knowledge Garrett turbochargers have Dual Ball Bearings currently installed from factory and not journal bearings ?
Have you found a very old GT3076 with journal bearings on it ?
If you install a DBB Gt3076R you will a 15% faster spooling time and response on your setup.
Tests from Garrett have shown that ball-bearings have up to half of the power consumption of traditional bearings. The result is faster time to boost which translates into better driveability and acceleration.
Also you said about rpm line i see that you have installed Supertech valvetrain i don't know if you have also installed titanium retainers if so, you can move your limiter a little bit safely untill 8000rpm with stock cams and hydro lifters.
Now if you install cams install either IE cams or CAT cams. CAT 3658 seems to have a good all around powerband but stay away from 3652's as those are more top end higher rpms.
CAST manifolds are made of cast iron of course and are used for durability and ability to handle the heat cycles (heat up and down) over and over. These manifolds will most often outlast the car if they are made well. For best results, make sure the runners do not fire against each other and wastegate placement is close to the flange.
Tubular manifolds are made out of mild or stainless steel. When it comes to these types of manifolds, you often get what you pay for. A cheap eBay manifold will often crack within a short period of time after install and should never be used. In that case use only repitaple brands such as Full-Race or 034motorsports. The biggest benefits of these manifolds are that they flow far better and make a huge increase in power with a larger frame turbo (GT30+). But they do sacrifice a little low end power and increase lag a couple 100rpms.
For fuel pump 340lph is enough, i am currently using Bosch 044 fuel pump. There is a
problem with most aftermarket intake pumps, they often starve for gas when the tank is less than 1/4 tank. So its best and cheapest to just add an inline pump. Also keep in mind that after you get to around 500whp, you will also be forced to increase the size of the fuel line and also even do a surge tank so you don't starve for fuel.
The only thing that could stop you from having more than 400bhp easily are the injectors.
630cc: 430whp
750cc: 500whp
Use only high impedance, wide angle spray pattern injectors. If not your idle and fuel mixture will be bad. I would recommend Genesis or Siemens Deka.
RS4 MAF is enough for the horsepower you are willing to make. I have chosen Mafless tune due to less problems without a MAF generally. I am not saying that with MAF you will have problems. It's personal preference after a lot of trial and error.
The Motronic 7.x Series is at least 10 years ahead of it's time. You can also use a mafless tune if you have a wideband motor and a MAP sensor of course
You want have any issues with ABS/ASR/ESP or mileage and such if you choose a correct tuner.
I chose Unitronic Mafless tune after various tunes with MAF sensors gone bad or off. it's just one less expense to think about for me. Mike from Unitronic tuned my car.
You can expect to see big numbers with your setup if you get bigger injectors than 630cc more than 430whp i mean and if you install a large port Intake Manifold it will easy as pie.
PS: Also make sure your clutch can handle the power SPEC all the way for me for that amount of power. It handles brutal accelarations and high rpm top ends without even blushing so to speak
And also install a big FMIC that can handle that amount of hp and an oil cooler if you are brutal with your car.
