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Discussion Starter #41
Stock catback is only a 15 hp restriction at 600hp, probably not it.

Also you should be able to hit full boost in 2nd gear easy. I hit 95% of my setpoint in 1st, 3rd is absurd to be checking on the street.
That's good to know. I don't know why it held better boost then. I'm just going to eliminate the turbo as a possible cause by throwing on some 15g's. I'm going to send these 13g's out too to get them checked. I originally bought them from Carl McEwen back in 2004.
 

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Invest in bigger turbines. That's where all the power is. Your just bandaiding an restriction by putting a bigger compressor wheel on and leaving the turbine alone
 

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Discussion Starter #43
I will throw on the 15s but regardless, even a small 13g should hold at least 15 to redline.
 

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Discussion Starter #47
Another update guys. I dropped the exhaust from where it connects to the mufflers and I held boost till redline. It was the stock exhaust causing a restriction.
 

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Do you have Cats/Precats? If so get rid of them. They fetch a nice price in the scrap yard and that is all they are good for.
 

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Discussion Starter #49
My precats are gutted and I have an aftermarket downpipe which replaces the cat. Either the stock exhaust isn't designed to hold more than 13 to redline or mine has a major restriction.
 

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Very odd. I bet it felt like a rocket.
 

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Discussion Starter #51
Very odd. I bet it felt like a rocket.
Yeah it spooled up faster and spiked more. I had to turn my boost controller down. I felt like I would hit a wall before above 5k now it just keeps pulling. I need to get an exhaust now. I heard the ebay ones that copied the tannabe design are good. I just want something that doesn't have drone. I can get a used borla for a good price but I heard they have a lot of drone.
 

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I wonder what is wrong with your stock catback? There certainly isnt a restriction that would choke up the turbos in a well functioning stock catback.

The Ebay unit is pretty nice. Decently loud. I cannot remmeber if it drones or not, someone will chime in, half the board has it, lol
 

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Discussion Starter #53
Ok, I ordered the ebay one. I wonder what it is too because it has a lot of flow and the sport/tour switch works. Can it be a weak turbo causing too much back pressure?
 

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Ok, I ordered the ebay one. I wonder what it is too because it has a lot of flow and the sport/tour switch works. Can it be a weak turbo causing too much back pressure?
The exhaust valve is probably stuck. Just because the switch works does not mean the valve works. The motor will turn but the line will just go slack and the valve does not move.

I read that a exhaust valve stuck in tour mode can cause you to lose like 1.5 seconds in the 1/4 on a stock car so I can imagine it adds a lot of restriction.


You can easily check if its in sport or tour by starting the car and then check if exhuast is pouring equally out of the 2 exhaust sides, if it is only going out the diver side it is in sport mode. If it is going out of both it is in tour mode.
 

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Discussion Starter #55
The exhaust valve functions properly. The reason I didn't remove the stock cat back was to retain the tour function to eliminate drone.
 

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Discussion Starter #56 (Edited)
Well another update. I installed the exhaust and now i'm getting boost creep again. I turned off my boost controller and it creeps up to 14.3 by redline. I'm guessing the back pressure that was caused from my stock exhaust was forcing the wastegates open. Looks like i'm gonna be adjusting pre tension for the 10th time :-/

Another thing I noticed is that i'm running leaner at WOT. I used to be around 11.3-11.5 now it's at 12. Can the new exhaust cause this?
 

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ok, so your initial problem was your 13g's not holding boost to redline with an aftermarket downpipe and gutted precats. So you removed the stock muffler and now it holds boost to redline, so your initial problem is solved?

Now, after fixing the initial problem, your new problem is that boost is always (or sometimes?) creeping past your boost limit. You think you never had this problem before because the previously restrictive exhaust was allowing the wastegate to open.

I'm not sure about that last thinking, it would seem to me that a less restrictive exhaust would allow the wastegate to open more easily, but I'd like to hear what others have to say. I'm curious because I'm getting boost creep with my 9b and I'm checking my rear wastegate this weekend, my front wastegate seems to operate as it should, though it was also suggested that I need to check my "preload", perhaps preload needs to be checked after any exhaust system change...
http://www.3si.org/forum/f35/overboost-issue-i-need-some-guidance-779042/
 

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Discussion Starter #58
Yeah, now that I think about it, it doesn't make sense but then again nothing seems to make sense about my car. I'm pretty sure my problem is too much preload, I'm going to adjust it again tomorrow. Here's a good article about boost creep. https://forums.nasioc.com/forums/showthread.php?t=477715
 

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Discussion Starter #59
Actually I figured out what happened. With less back pressure due to a more efficient exhaust you increase the flow capacity. As a result you decrease the pressure on the wastegate valve causing it to stay closed and boost to creep. Solution is to decrease pretension or put a lighter spring.
 

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good boost creep video here


After watching videos, I learned that the reason why boost creep happens, AFTER making your exhaust flow more, is because exhaust is now flowing so much more freely through the compressor path that the exhaust gas doesn't need to go through the more restrictive wastegate path even if your wastegate is wide open.
So, porting the wastegate path, to make it flow very freely, is the best solution to address this OR convert to external wastegates.
 
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