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Source of boost pressure for electronic boost control


Paul Moran
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I've just installed a larger turbo on my EJ20 and am worried that running the electric boost control feed from inside the intake (after the throttle body) will not allow the waste gate to open while under boost if I take my foot off the gas. 


I currently have a hose directly from the turbo outlet to the waste gate to run off the default 5lb spring, but want to reincorporate the EBC as soon as possible.


What should I use for the source of the boost control?  Pressure before or after the throttle body?  Does it make a difference because as soon the LinkPlus sees vacuum from the MAP tied in after the throttle body it would stop cycling the EBC, right?


Is it safer to just add a by-pass/blow off valve before the throttle body?

Paul...

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Let me clarify my concern... If the EBC pressure source is the intake manifold after the throttle body, I'm worried the following sequence will occur:


1. at 15 lbs of boost, the throttle is slammed shut

2. The LinkPlus sees MAP vacuum and stops cycling the boost controller

3. The waste gate closes

4. The engine continues to spin, causing the turbo to build a lot of pressure between the turbo and the throttle body.

5. The throttle body butterfly bends under the pressure...


Paul...

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This is the exact reason why blow-off valves were invented.  If the throttle is slammed shut, a large rush of air will build up against the throttle plate, then bounce bake and smash into the turbo.  If you are lucky it will all just bounce around until it dissipates, but if you are unlucky it will damage the compressor wheel...  It doesn't really matter what the EBC is doing as when the throttle shuts, there will be too little exhaust flow to keep generating boost anyways.  Put a good blow off valve somewhere before the throttle body (usually placed after the intercooler).  When the throttle is hut, the pressure differential (vacuum on one side from the manifold and pressure on the other in the intake pipe) will cause the valve to open immediately and dump all that air that is building up against the throttle plate.  Will also help to reduce the amount your turbo slows down during gear changes...

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Thanks, Ashley - you've confirmed that there isn't a good solution except a blow off valve.  I'll keep the boost down until I can install one. 

Is there a preference for the source of the boost pressure to run into the EBT - just outside the turbo outlet or from inside the manifold after the throttle body?

Thanks! Paul...

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I always though that the plenum was a good spot, after all thats where you want to keep the boost pressure constant, but this can cause additional delays in the control loop and create boost spikes (which should be able to be tuned out with EBC).  But some say the turbo outlet, is better!  Just depends what actually works best...

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