Aps 3.5"

Hi all,
I've been searching for a good exhaust for my SZ49. Currently I have a 3" non-name brand downpipe with a 2.5" taper, then donut gasket, then 3" cat-back with 4" axle back section right before the muffler. It seems the turbulence from all the diameter variance could hurt performance quite bit. So I thought about buying a divorced wastegate 3.5" turbo-back from APS. It seems to be quality but the divorced wastegate design worries me that I might see boost creep because the wastegate flapper might not open fully because of the splitter in the downpipe (most caeses of creep are on the VF39 with slightly raised edge on the wastegate hole, not sure how different on the SZ49). I also have a helix 3" downpipe sitting in the garage and really debating if i should just slap that on and call it a day. Any thoughts?


As a counter point to the divorced wastgate leads to boost creep argument, I have 2.5” divorced wastgate downpipes on my 300zx TT and it seems to never have any boost creep at all. As matter of face the divoced wastgate leads to two separate pipes and rejoins 10-12” inches after the turbo. The turbo spools faster have more torque and power delivery comes on more linearly. It also seems Audi S4 and Porsche Turbo also have this same design from the factory. I know they are different engines and setups and whatnot, but it seems the theory of divorced wastegate generates more power is a fact.

So any insights on the subject would be nice, to either pick 1 of the following options
1. use Helix downpipe to have 3” back to the axle back and becomes 4”(not sure how bad this would be to have different diamters)
2. buy a used APS 3.5” and which is about $500-600 extra over option 1, and run the risk of boost creep

thanks for reading,
sincerely,

 

You won't have to worry about boost creep with a SZ49.
Those are great turbo's.

I wouldn't worry about going to a 3.5" exhaust.
+1 on what Alex says, use what you've got with a good axle-back.

 

Helix downpipe and Invidia catback or Invidia TB FTW!! :banana:

 

i made good numbers with my blitz cat back and a hi flow cat... the blitz does taper some where it meets the downpipe... not sure if it tapers all the way down to 2.5 inches though... leads me to believe that the real restriction is somewhere else

 

I had some issues with my APS 3" causing the boost to creep but I think that on a larger turbo you shouldnt have as much of a problem.
Put the helix on and see how you like it, I doubt the 4" muffler is truly 4" all the way through. I'm also skeptical of how much the turbulence back there would even hurt the overall flow since the exhaust has slowed down a good bit as it cools towards the back of the car.

 

+1
This is my setup and i love it. Not to loud not to quite

 

thank you all for the advice, I really thought the divorced wastegate design + 3.5" all the way back would add some power (more interested in the torque)...but it seems using the helix downpipe is more "economically sound" <--ya, can't you tell I'm at the MGT buidling @ Tech square

 

i work in the centergy building... u can hear me every thursday