Best BT for 500 hp?

[SpeedRebirth]

Originally Posted by EmPeEs6 I run a common 3" cb...

I have the same catback and it's only 3" until it divides at the rear axles. Where they become like 2.1" each. See pic below. It also has a 2.5" flange to DP, unless you welded on a bigger one.
My plan is to replace the flange with a true 3" since my DP is 3". That will lessen turbulence and whatever small restriction it causes. Now that I have a forged engine and BT I will also consider a exhaust cutout somewhere between the DP and axleback just to see how big of a restriction our catback really is, but that won't happen until im fully tuned.

As a test you could always disconnect the catback from your DP to see how it reacts

[EmPeEs6]

I don't think that this reduction in diameter at the splitted end is that much of a restriction for the Ray/Simons cb, but I'm curious what you will find out...

Meanwhile I regret that I didn't take some combination of BT + suitable exhaust manifold/downpipe like the ones from EFR or PT...I'm sure that these flow significant more air and thus generate more top end power.
On the other hand, running such a combination I would have needed port injection, which I didn't want to install so far, and now I'm thinking of getting at least a CP-E manifold and maybe installing some GTX compressor wheel as I did on the S3 before and which had a positive effect on power output.

My aim is to get at least 380 awhp with just wmi (on ~50% meth) and almost no power drop above 6k.

[EmPeEs6]

Update: The S4 isn't as "bad" as I temporarily thought, i.e. it generates massive boost/load from 3.5k on and also has much potential up top (see also: Problem with boost control on BNR S4 setup).
I will post another VD graph as soon as I optimized my current tune, but I probably will be stuck to 380 awhp (max).