S4 Twin Scroll BNR Stage 3.
 

Should I keep the Twin Scroll setup on the S4 if going to a BNR stage 3.

Car will be used as a full street trim emissions legal and weekend Time Attack. I would like spool up and the torque.

Anybody have experience with or without twin scroll?

Thanks,

I was going to go Stage 4 but don't want the lag. There was enough lag on my To4B turbonetics turbo.

I have the twin scroll and BNR stage 3. Still laggy, but pulls hard once boost kick in.

GO TWIN SCROLL!! i found it much faster smoother Spool than the a similar sized turbo i was using that NOT twin scroll..

What is your boost pattern like? Gonna run water injection. Run more boost maybe go stage 2?

The fact of the matter is that twin scroll works. Remove the twin scroll and you will experience lag from hell. I have the equivalent of a BNR stage 3 and my S4 manifold came with the twin scroll removed. I did have an S5 manifold and turbine housing, but it's a messed up story as to why I don't have that any more. Going from the S5 to S4 without twin scroll is a HUGE difference in lag.

Also, from my experiences, S4 and S5 feel like there is no difference in lag. Some will say the S5 is quicker to spool, but I've personally never noticed a difference. In all likeliness, Mazda went to the S5's divided design because it offered the same or better spool characteristics without the extra mechanical linkages and leak points.

The good thing about the s4 turbo is the bnr rebuilds actually make bigger wastegates. The s5 wastegate can only be ported. I guess that's only a problem if you can't get the boost under control.

I like my s5 though and did not have any problems with a to4b and clipped turbine wheel

My boost comes on late 4000rpm or so. I run water inj. post intercooler. I run about 10-11 psi of boost and water come on at 5psi. Boost holds steady to redline. Laggy as hell. my stock turbo would break the tires loose at the beginning of 2nd gear, now they don't break loose until the top of 2nd gear. old HP 200, new HP 272.

I have only driven my car without twin scroll since I do not have the solenoid to properly activate twin scroll on my Megasquirt (work in progress...). My current externally gated manifold has the flapper removed. I see full boost around 4000 RPM. It is pretty laggy and that is my only complaint.

The twin scroll is NOT a big deal to leave intact. Even if you rip out all the stock "crap" you can put in a simple RPM switch and use an old solenoid. With a standalone, it's easier still. Solenoids are everywhere. I did this with my E6k and it was a piece of cake. It works! There is no reason not to use it with the old S4 style manifold & turbo.