Quote:
Originally Posted by SPOHN
How much more time does it take on average to tune the car since the fuel pressure will be different from the get go with a return system.
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If you choose to not hook up the fuel pressure regulator vacuum/boost reference line, and set the fuel pressure to stock, then the tune will not be effected at that time.
Anything over 10psi and I would recommend using the vacuum reference to keep your fuel pressure differential high. That means: If you have 52psi rail pressure, and 10psi of boost, you are effectively operating at 42psi fuel pressure. If you were 20psi boost, you are at 32psi effective pressure. So, once you start going nuts on the boost, you want your fuel pressure to climb with boost. Over 10 psi, hook up the regulator vacuum reference to a boost only pressure source. This would be a charge pipe before the throttle bodies. The VVEL system causes swings in manifold vacuum that are not consistently linear with engine load. Therefore, the manifold vacuum is not a direct indication of engine load, and therefore we do not want the fuel pressure regulator reacting to it. We want it to see boost only with VVEL. I am sure it would still work fine, but it is theoretically incorrect.
You can, if you choose, use the boost reference at any boost level you want. If you were say, trying to get the most of some undersized injectors, then you need all the help you can get, that few psi of fuel pressure which help.