My feedback on the DIY Tymar. Hope it helps
I've got an obs, like you. I did the diy Tymar a couple weeks ago. My engine is all stock right now. I could feel a slight power improvement. You would probably feel more,because your running a chip. Nothing wrong with improving airflow.I'm running a turbo back Magnaflow exhaust,no cat.There is almost as much turbo noise coming from under the hood, as what I hear from the tailpipe. There is a throatier sound from under the hood too. I like it. I don't know about EGT temps, as I've bought gauges, but I haven't installed them yet. I didn't have access to a 4" exhaust 45', or a welder to make one. I bought a sch 40 pvc st 45', and a foot of 4" sch 40 pvc pipe. I only used about 4" of the pipe. The pvc OD is about 1/16" bigger than that of the steel exhaust pipe. I had to use a little dish soap as lube to insert the 45' into the filter. Likewise, to get the pipe into the intake boot. If you do it this way, be sure to use enough glue, when you glue the 45' to the pipe. When you insert the pipe into the 45', give it a twist to help it seal. Put glue on both pieces being glued. Wipe off any excess glue immediately. Looks better. Paint if wanted.