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beepbeep beepbeep is offline
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Join Date: Jun 2001
Location: Sweden
Posts: 5,565
First of all: I don't think you shouldn't hear detonation at 0.9 bar in otherwise healthy 930, at least not if using quality fuel.

Second: the reason that boost went up after muffler install is that backpressure after turbo is lessened. Exhaust gases will take the path of least resistance. If backpressure going into turbo is high, more gases will try to escape trough wastegate and you'll need harder spring. Is backpressure is lower, bigger portion of gases will go trough turbo and boost will go up unless spring tension on wastegate is lowered. This is the case with simple non-EBC installation where plenum pressure actuates the wastegate directly. As long as spring-pressure in wastegate is preset to give lower boost than you want to acheve with EBC, things are OK. This is called "base boost". EBC will only allow you to get boost higher than base boost. It cannot reduce the boost below basic spring-tension boost.

In your case, I suspect you are using OEM 0.7 bar boost spring with EBC set for 0.8 bar. This worked before and EBC only had to vent enough air from singnal line going to wastegate to achieve extra 0.1 bar.

Once you installed free flowing exhaust, I suspect your base boost went up to 0.9 bar. Thus, your 0.8 bar EBC configuration is overriden by spring tension and EBC is out of the loop and just hanging on for a ride. It cannot control the boost anymore unless you ask it to boost more than (you new) base boost.

To test for this, disconnect EBC completly and run the wastegate directly from plenum. Note the boost. That boost will be your base boost and you EBC will only be able to raise it, not lower it. If your base boost is 0.9 bar, you will need to install softer spring in the wastegate in order to restore EBC authority over boost.

I suggest using base boost that is at least 0.2 bar lower than target EBC boost, otherwise EBC won't be able to control boost in stable manner.

With other words, pick a spring that gives you 0.6 bar of base boost if you want EBC to hold 0.8 bar of boost and higher.

Is my explanation too complicated?

Regards,
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Last edited by beepbeep; 06-23-2008 at 02:49 PM..
Old 06-23-2008, 02:47 PM
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