Custom Exhaust Size For Stacks

[KHeine]

Well, I'm still in the midst of bombing my 89 Cummins. Of course, the list of things I want to do keeps growing as I work. Here's my issue (with a little background): I went with Pier's HX35 Turbo with the 16 housing. I also added an intercooler, and I've mostly been doing a lot of custom diamond plate work. I am custom building a 4" stainless steel exhaust. It is currently 4" right from the turbo back, no muffler. Now I decided I definitely want stacks. I was looking at some nice 5" ones. In order to stay within my extremely limited budget and to work around the custom built bed on the truck, I'm custom building the setup. I was originally going to go with 4" pipe between the stacks and then adapt to the 5" stacks before I come up through the bed, since I can do this in stainless DIRT CHEAP! My question is, will this create too much backpressure and affect my EGT's? Or will it even out since I did 4" all the way to the turbo and have no muffler? I custom built a tranny crossmember which allowed me to run the pipe pretty much straight back from the downpipe, so there really are no bends past the downpipe. Do I need to go with 5"? Any help is greatly appreciated! Oh yeah, I'm also cranking up the fuel and evetually putting in some POD's. The intercooler is from an '05. I shortened it a little and modified the radiator support to fit it, so it is very large with 3" inlet all the way into the intake. Thanks in advance!