I am getting close to building my truck for my s475 1.32 turbo build.
I have a question to the down pipe design. How far back should I go with 5"??

I thought about a elbow out then make a long transiston to 4". Then down the back of the truck. Let me know what y'all do and think

 

Why step down if your alrdy going 5 inch go 5 all the back.

 

That's a huge freakin pipe. Making me think twice about running a bw. What if you run a short section of 5" with a cut out that you can uncork for track duty and y it into 3" or so the rest of the way back.

 

I step them down right after the outlet to 4" No need to try and squeeze an overly huge down pipe when 4" will easily flow for well over 1000hp.

 

i remember reading somewhere that about 18" of 5" was needed before transitioning to 4" but im not sure if that was a load of crap or not. it came from a very reputable source tho which makes me wonder.

 

5" just matches the casting.
No need for it on that turbo.

 

The 1.32 ar housing has a 96mm turbine so that's a 3.75" wheel. 4" is all the down pipe you need for that wheel.

 

I ran a 5" pipe, and if I had to do it again I would just use a 4", same power really. Spool may be a little better on the 5" but thats it.

Dumping out the fender made it spool 2x as fast, but still didnt help overall power.