So I took the downpipe off to investigate my overboosting problem as discussed in this thread: http://www.miataturbo.net/forum/showthread.php?t=24951. Maybe somone would like to give me some opinions here.
Exhibit one is a video of how far the wastgate opens with the downpipe and without (Ignore the ghetto rod end. Paul made it for me when mine got lost at his place when driving with the wastegate wired open):
Here is a pic of where the flapper is hitting the inside of the downpipe:
I don't see how I could take much off those areas because it'll weaken the weld I imagine, and the wall of that pipe is not that thick. It does hang up on the inside of the downpipe when you move the wastegate by hand.
Here is a pic of the wastgate port. If you look at the shiny rim of the port and the darker rim at the edge of the flapper it appears it is already ported but tell me if I'm mistaken.
Also it appears that I had a slight exhaust leak on the wastgate tube. I can't imagine that that would cause my overboosting though, right?
Finally, required cat pic. My friend's cat loves hanging out in and on the car.
Well the wastegate port definitely looks like it has been ported, but that doesn't complete the job. The way porting an internal gate was explained to me also involved removing some material from inside the turbine housing in a straight line leading up to the port in order to give the flow a smoother and less turbulent path out. I've been searching the net for a write up I found a while back that shows how to do it, but have come up with nothing now.
How is that not a problem? I have to have the wastegate adjusted so that it's slightly cracked open at idle to not hit overboost protection really early. So I'm loosing spool down low and I'm still hitting overboost protection before redline. It'll get to about 13.7psi and cut out at ~6800rpm or lower. And that's with EBC off.
I'm not sure if it's related, but STI's have a similar weird problem when you go to a catless downpipe in the winter, even with the rest of the exhaust system stock. If you pin the wastegate open, it never makes enough power to make enough exhaust flow to creep, but if you wait too long and start opening the wastegate near the boost limit it'll overboost and hit fuel cut. The solution on those is to start ramping up the wastegate duty cycle earlier in the ECU. I'm not sure why that works, but it seems to FWIW.
There is a "trough" leading from the turbine entry to the port. I did happen to notice that before the turbo was installed. So it seems the wastegate was ported correctly. Cripes....
You cannot tell from the photos if it has been ported. I need a photo of the bolt holes more to the right. And also of the other turbine flange. Chances are if there is a "trough" in the turbine inlet flange, it is ported.
It will not hurt to take a grinder to the inside of the downpipe. Just don't grind off too much.