Cant figure why its overboosting after new turbo???

[Way2QWK]

This weekend I installed 42.5 lb injectors and a TA-49 turbo on my friends stock Buick. Install went good without a problem. We replaced stock stuff with,.....new turbo, wastegate(not HD accuator), GM boost line with "y" fitting, intercooler hoses. I set the wastegate rod to the longest setting and went for a test drive and the boost would go to a easy 18 psi (let off due to pump gas).

I have since swapped everything that has to do with boost control with new parts from my Buick. Here is what we did....

1. lengthend wastegate rod all the way out during all tests
2. changed new wastegate back to original stock....since changed back to new, thinking maybe old one was leaking...no luck
3. Checked new "y" fitting for correct size hole.....ok, put old boost line back on with "y" fitting, put known good "y" fitting from my car on no luck.
4. replaced wastegate solinoid with new delco....no luck
5 by-passed solinoid and "y" with vac line going from comp housing to wastegate.....no luck 10psi in 1st gear 18 in 2nd......
6. If we undo the wastegate from the puck the car will not make boost just like it should. If I slip the rod back set to the length that the flapper is barley open it still makes no less that 16 psi
7. Puck on downpipe is not stuck moves freely

After all this the only thing i can think of is the hole in the exhaust housing needs to be enlarged for the exhaust to bled out easier alowing less boost. But its just a stock motor with a little 49
But why cant we get boost down to say 10psi. We dont want a bleeder/grainger valve or a bandaid fix.
------------Current set-up on overboosting car

Stock original 15k motor
K&N with hard Maf pipe
stock intercooler
new adjustable wastegate
adjustable FPR
walbro 340 hotwired
009 inj
93 octane JL chip
THDP
precision 3000 stall
new TA-49

 

[Slow91z]

My car does the EXACT same thing...if you figure it out let me know...I enlarged the hole in the Y and now I tighten the actuator more to bring the boost back up to stock...I know this isn't what you were looking for, but this is the temp fix I am using till I can figure it out, I figure I can just get a new orfice from John's Performance After I get it fixed...It just screws into the y anyways so I have to enlarge the hole in the Y sooner or later to install the one John sells.

 

[Way2QWK]

I hope this is not something we have to live with. What is the point of a stock Buick that cant run on pump gas!!

 

[Slow91z]

Depending on timing and quality of fuel, say around 16-17 Pounds of boost.

 

[Mike Licht]

Sound to me like the wastegate hole in the turbo is too small. Compare it to the puck and see if it can be enlarged and still seal up
Mike

 

[Slow91z]

Hey Mike, I agree that that could be his problem, but I still have a stock turbo on mine??? I can't figure it out.

 

[Way2QWK]

thanks for the replys

The hole in the exhaust housing could be enlarged/ported A LOT, the puck from the THDP is huge. Does the 49 turbo flow that much more exhaust than the stock housing to cause this. I was just looking at pictures I took of both turbos next to each other on the bench and the wastegate holes on the housing look the same size. stock to new TA49

I still dont understand why this setup is yielding more boost than my car did with a 10 sec motor, 66mm turbo and stock wastegate solinoid, "y" fitting and HD accuator. No mods to exhaust housing needed and I could run as low as 5psi through the gears if I wanted to ???

 

[Dr. Jeckel]

My car had the exact same problem but it happened whenever I changed from a stock chip to an aftermarket one.
With the stock chip it would run steady 14psi with lots of KR but when I put in the RA 93 or thrasher 92 it wouldn't stop boosting. Replaced wastegate solenoid and tried everything. Finally just had to use a manual boost controller to do it. I'm not sure what EXACTLY controls the solenoid but for some reason it didn't work the same with the different chips as oppsed to stock. It doesn't seem to be a problem that alot face so it leads me to think it has to be something querky in the ecm and how reads other things to operate the solenoid.

 

[Slow91z]

Hmmm interesting...Mine does it with the stock chip, and it's much worse with a different chip, with a hypertech (don't like it anyway) it won't stop making boost and with my dynotech stage 5 boost jumps about 4-5 PSI...I dunno, I guess I'll just do it my way...It works.