To De-Smog or not to De-Smog...
You're right, but he didn't fab it, he bought it off "Mister Twister", who until very recently has been trying to substitute ... -- see threads
here and
here and (especially)
here.
Dan and Twister have been at it for a while. The basis of Dan's objections, as I understand it, has been a lack of empirical data to back up Twister's claims. FWIW, I do not support Twister's claims for this pipe, either.
I purchased it wanting something that would work with a larger pipe than the stock manifold would support. The Super 6 exhaust manifold that is supposedly able to mate up with a 2¼" pipe seems to be made of unobtanium in these parts, hence the purchase of Twister's piece.
In it's defense, I will say that it is well made and has proven durable for the 15,000 miles I have used it. In my own tests, removing all the variables I possibly could, I got 3 mpg better gas mileage on the highway and another 7 mph top speed. These were areas I wanted to improve. The changes were the installation of this pipe and a 2¼" exhaust system.
The car runs like crap when cold, but it did that with the stock manifold. I don't see any gain or loss in that regard. As for changes in exhaust flow, I couldn't tell you.
The entire point of the whole EGR thing is that to eliminate it, you have to isolate the intake from the exhaust system and make sure a vacuum loss is not created in so doing. The choice to do this is the reader's.
IMO, EGR shot drivability of the internal combustion engine in the head. It has not been until fuel injection and closed-loop computer controlled emissions systems were implemented, that EGR has been able to do the job it was intended to do with minimal adverse impact on drivability.