BLUE TII

iTrader: (9)

So I sent my BNR Stage 4 stock turbo back to Bryan to get the "P" trim exhaust wheel clipped again as I felt it was choking the engine out unclipped.

I put my STOCK turbo in the turbo housing that is among other mods bored for T04 "P" trim exhaust wheel. There is more than 1/4" clearance all the way around the exhaust wheel, but I bolted on my external wastegate just for good measure.

I was quite surprised when the turbo still boosted fairly well- almost as well as my BNR turbo. 1-3 psi by 2,000 rpm and full wastegate boost (7.5 psi) at 3,500 rpm.

Boost starts dropping pretty hard ~4,500 rpm and the wastegate shuts again. I don't know if that is because the stock turbo can't flow enough to boost the big streetported motor or if there just isn't enough exhaust energy to spin the compressor fast enough to maintain boost.

Anyways, just an interesting experience. Exhaust wheel to housing clearance doesn't appear to be a big deal with the rotaries.

RacerXtreme7

iTrader: (2)

I'd say that due to the small internal passages (even though you bored the scrolls out larger AND bored it for a P-trim) along with your street port makes enough energy that it spools up then as your asking for more boost (or at least trying to maintain boost at higher flow) those big *** gaps aren't allowing enough work to be done by the exhaust gases to maintain boost pressure compounded by the nice flowing engine you built and the tiny stock compressor. To sum it up, what you said lol except the last line....... Clearance in any turbine is important especially when your really asking it to do work (READ: maintain boost at higher RPM's).

The stock turbine really has some tiny *** inlet/scrolls. Don't let looking at it fool you. The mating surface of the turbine isn't perpendicular to the inlet/valute runners. So measuring the actual inlet footprint does not give a accurate volume / area / runner diameter. Stuff it with clay, then pull it out and cut the clay perpendicular and you'll see just how small I'm talking about.

Love your car and the work you do.

~Mike..............

Turblown

iTrader: (12)

Sounds like the compressor can't keep up, that or its the tuning.

Would be interesting to try just a P trim turbine upgrade on a stock turbo.

BLUE TII

iTrader: (9)

The stock turbine really has some tiny *** inlet/scrolls. Don't let looking at it fool you.

Yep, the stock inlet/scrolls are tiny for high velocity. I do still have stock valute runner after the wastegate passages and leading to the larger scroll slots.

The mating surface of the turbine isn't perpendicular to the inlet/valute runners. So measuring the actual inlet footprint does not give a accurate volume / area / runner diameter. Stuff it with clay, then pull it out and cut the clay perpendicular and you'll see just how small I'm talking about.

Since you were kind enough to compliment my work I will bore you with some details. Don't know if you saw the latest pics of the turbo in my engine rebuild thread, but I did address the issue of stock inlet not being perpendicular, or the dreaded cheated radius bend

I ported the stock manifold so it is only ~11% decrease in volume at the outlet and worked in a flat roof with actual radius leading to the turbo housing while putting a bowl in the bottom of the manifold leading up to the turbo housing. I ported the turbo housing to match continuing the top and bottom radii and kept the larger runner volume up to the wastegate orfices and then pinned them for good alignment.

Thanks for the reply! It just blew my mind it still had so much boost response and Bryan @BNR seemed quite surprised as well so I thought I would "share" :P