how much will my stock catback keep my boost down to?
 

Well I have had my turbo rebuilt. Have had all my vac lines redone. The most boost I can get is like 10psi with my boost controller maxed out. Could this be from my stock catback? If not what else do I look for? I have a full 3" TID and 3" DP from the turbo to the stock catback. WG is ported fairly heavily but a new flapper in on it so it covers the entire hole.

Just curious. When you say stock cat-back, are they the factory "Y" pipe and mufflers, or aftermarket pieces. The factory mufflers flow quite well.

Its a complete stock catback: y-pipe, piping and mufflers.

Well, I'd say that's about right. Read some past posts, and most are seeing 10/11 psi, just as yourself with similar equipment. I'm sure no expert in this area. Read some of the posts and you'll see some running 13/15 with quite a few mods.

But this is with a boost controller though.

I would have to say it is not your stock catback that is keeping boost levels down right now.

On my '87 TII when the only mods were - hugely ported WG, 2.5" downpipe/presilencer, FCD, walbro and rewire and TID mod

Boost would creep to 14psi near redline in 5th.

The compressor upgrade you have should increase max achievable boost/boost creep since you have upgraded compressor side flow and NOT increased exhaust turbine side flow.

Or have you increased exhaust turbine flow? Is your exhaust turbine clipped? Damaged?

What is your intake restriction situation. On my previously mentioned set-up there was ZERO boost creep w/ out the TID mod.

EDIT- Oh, did you set-up your AF ratio on a wideband? Really excessively rich AF will KILL boost.

Well my turbine wheel was damaged so I had it rebuilt and had a stage 3 turbine wheels put on. That is just what the shop did yesterday. My car is not tuned right now. Just have 720 secondaries and a walbro pump basically. I'm going to have it dyno tuned when I get it back though.

A HA!

Stage 3 exhaust turbine probably means it is a T3 stage III exhaust turbine (very close to stock TII diameter, but a more free flowing "trim".

You do need a more free flowing catback to take advantage of the more free flowing exhaust turbine. On the upside, once you have the exhaust system that can support the increased turbo exhaust flow you will have MUCH better high rpm power.

You might want to be careful how free flow you go on your catback. I have a T4 "O" trim wheel clipped 15 degrees (2 to 3 stages in flow above the T3 stage III trim) in my DUAL wastegate '89 hybrid and my 3.5" turbo back exhaust causes boost creep past 20psi by 4,000rpm.

Well I am not positive what turbine wheel it is really. All I know is they had to machine the turbine housing to get it in there and before I had a p-trim turbine wheel. I wish I had boost creep(kind of). Guess I'll have to get a catback soon.

THere is no way you had a 'Ptrim' turbine wheel in your stock TII exhaust housing. The P trim wheel is larger than the O trim that BLUETII is using. Add to that the fact that you now have a smaller exhaust wheel than that and it would be impossible to reuse your turbine housing for a T3 wheel if it had already been machined for a larger T4 wheel.

Daniel

Well I got my car back and boost will go up as much as I want. I still have no idea what turbine wheel I had or actually have now.

This might help w/ exhaust side comparisons.

MODEL PART NO. PRICE TRIM EXDUCER DIA. MAJOR DIA.
T3 20279 $ 218.00 STANDARD 1.898" 2.319"
30361 196.00 STAGE II 2.122" 2.559"
30310 196.00 STAGE III 2.229" 2.559"

T4 20301 218.00 N 2.071" 2.922"
STD SHAFT 20302 218.00 O 2.296" 2.922"
STD SHAFT 20303 218.00 P 2.544" 2.922"

T4 20460 402.00 O 2.296" 2.922"
BIG SHAFT 20333 313.00 P 2.544" 2.922"
BIG SHAFT 20366 492.00 Q 2.693" 3.111"


As you can see the major diameter is the same on the "O" and "P" trims but the "P" trim exducer is much bigger. W/ the "P" trim the stock exhaust housing would have to be bored hugely where the Exducer resides and taper back down to the stock-ish diameter to mate w/ the downpipe.

EDIT-
glad your turbo is working for you now!