Divorced wastegate downpipe port shroud fouling the wastegate?
 

We borrowed a downpipe from a friend who has his car out of commission for a while (some odd delusions on getting debt free by eliminating fun from his life for a few years:facepalm:). Anyway, his is an old BEGI kit on a 1.6. He has a gt2860. Before he put his car up on jackstands semi-permanently, he had been having a problem where his turbo would build boost super slow, and if you stayed in it long enough, overboost badly. We have a GT2560, and when we borrowed the downpipe from him, we had roughly the same problem. Still fairly quick to spool compared to his, but easily overboosted.

We determined that the port shroud on the BEGI divorced downpipe down tube was fouling the wastegate flapper door. What's up with this? This is the old BEGI downpipe setup, that is interchangeable with our original Flyin' Miata FMII kit DP. Was it designed around a thick turbo to DP gasket? Not for these turbos? Intended to have the port shroud clearanced as part of the install?

Any insight?

sounds like the flapper is stuck.

make sure it moves freely and easily

it moved freely and easily on both turbos. there was no problem on our car with our turbo with our flapper with our down pipe. we switched to his downpipe with our everything else, and the problem moved from his car to ours. We clearanced the wastegate port shroud, and the problem went away. It is not a stuck flapper.

I think Scott's turbo is just too big for his 1.6, that is why it's slow to build boost (at least that is what it felt like when I drove it on the cank that time). The overboosting is another story.

I haven't seen this downpipe, but does the wastegate flapper open ALL THE WAY? Some downpipes have enough play in the mounting bolt holes so that the flapper will hit part-way sometimes, but then when you re-install it, it will open just fine.

What size is your exhaust? some people with 2560s report problems where the internal wastegate is just too small when they have high-flowing 3" exhausts. I have been lucky enough to not have that problem, but porting the wastegate seems to help people who do.

2860 isnt big for a 1.6L, unless it has a huge turbine A/R.

And it didn't spool THAT slowly, if I remember right. It was annoyinly slow for autocross, but about how I would expect a turbo of that size to spool on a 1.6. That was a couple years ago since I last drove it, though, so I could be remembering wrong. I would say it had full boost around 4k in 4th gear?

full boost around 4k in 4th gear after going WOT at 3k, but full boost at 4500 or so after going WOT at 4k. at least that is my recollection. It has been a long time since I drove it too.

.64 I think.

Andrew says you could feel it in the actuator, and with the bolts loosened, you could hear/feel/see the physical interference. He messed with clocking/adjusting laterally with no luck, then clearanced the shroud a bit and it fixed the problem 100%.

The exhaust is currently 2.5" DP with the divorced wastegate tube (around 1") and then into a 3" cat, and out of the 3" cat into a custom made aluminum adapter (~1/4" thick) transition to a 2.5" exhaust. Hey, it was the day before the race....we got it running with no leaks!