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Re: Alternative to APC upgrade/tuning (long)
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Posted by JT (more from JT) on Mon, 29 Sep 2003 17:36:31 Share Post by Email
In Reply to: Alternative to APC upgrade/tuning (long), TurboDave, Sat, 27 Sep 2003 20:33:30
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If you are interrupting the "controlled" manifold pressure to the wastegate, then you are bypassing the APC module, preventing it from doing its job.

The APC works off of a pulse width modulated (PWM) low impedence signal via a BJTFET (transistor). APC boxes work better than a simple dawes type device because they hold the wastegate completely shut unless RPM/Boost require it to be open. Once a boost threshold is hit, the APC closes the solenoid, allowing the wastgate to open a proper amount required to maintain max boost. Some non-Dawes type devices on the market (i.e in-line pressure restrictors do not work well because they open the wastegate as a function of boost, meaning you will bleed off exhaust even at low boost levels. This means more required time to reach desired boost.

Many people run a "shortened" wastegate rod with no APC. This is definitely not as good as APC because the wastegate diaphragm uses a linear spring which opens as a linear function of boost. Again, causing more time for spoolup.

With a dawes type device you provide a leak path of boost to atmosphere (if not spliced back into the post AMM intake somehow. This would potentially cause the engine to run richer than wanted unless properly calibrated.

A PROPERLY modified APC box gives you the best performance out there purely on the principal of a PWM. Case closed.

posted by 68.248.1...

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