Monday, Mar 26, 2007 at 21:42
Hi Leroy,
You have put forward some good valid questions. I’ve seen too many people block their EGR off, but fail to do the necessary mods to the turbo control system and eventually fall into the overboosting scenario.
If the EGR is blocked, then boost should be reduced and this is very simple and easy to do. If you don’t have a boost gauge installed, then 1/3 to ½ a turn on the boost limiting screw should do the trick.
After doing that you’ll still notice (if you have a gauge) that boost will drop away, even if you apply more throttle, because the system is trying to supply EGR. This is why I have bypassed the VNC control solenoid valve and fitted a manual boost controller so that the turbo works more like a conventional one. (
http://users.bigpond.net.au/conody/Images/Boost Control.jpg )
This system allows me to adjust the maximum boost that I want to run and I can adjust the rate at which it spools up with the in dash needle valve boost controller. It eliminates those high boost spikes and boost reacts only to load and throttle input. It’s a far safer system, but doesn’t allow for EGR and emission control. I have also removed my cat converter and run a 2 ¾” dump and 3” flow through exhaust. With this setup, my EGT’s rarely exceed 300c post turbo.
Another thing to note is that my maximum power is made at 16psi of boost. Over 16psi it made no more power, so why does Nissan run them at over 20psi? I would suspect that it’s for emissions, because it wouldn’t be doing the motor any favors.
To answer your other question “if the boost decreases to allow more EGR flow and it's blocked what happens?” You simply loose power.
Chaz
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