The local exhaust guy, Dave, wants to leave in the factory y.
He wants to cut off the left side and just cap it.
Then run duals back to two Flowmaster 50's and out behind each wheel.
He wants to do this because he said the factory y is stainless steel.
Not sure about this. Has anybody else ever see it done this way?

 

It can be done that way. This will leave an area of disturbed flow at that area. You shouldn't notice it, this is just a note for optimal flow engineering. It's better to cut the passenger's side pipe off just before the Y-intersection (as close as possible) and have that side's pipe expanded and CLAMPED on. This method gets rid of the substantial "S" in the pipe just behind the factory Y-intersection.

 

Max, I've got a '97 4.6, 4x4 s/cab with the 4R70W transmission and a Gibson 3" catback. Would I be correct in saying that I need a 2.5" into 3" y collector? What length should the y pipe be? Also, I've read about the 90 degree mandrel bent pipe you brought along for your install, what were the dimensions of this piece? If you happen to have the part number of the correct y-pipe handy, it would be appreciated. Thanks in advance.

 

The Flowmaster Y-pipe comes in one length; it's part number Y250300A; it's 2)2.5"in and 3"out. The 90 that I used is from J.C.Whitney P#81SY2953P; it's 10" both ways by 2.5" on each end. The 90 can then be shortened, swaged as necessary, and costs under $10. Both of these parts are aluminized steel; not stainless steel. The cheapest place to get the Y was www.racerpartswholesale.com

 

Thanks Max!

 

You're more than welcome. Good luck with the install.