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Coenraad said:
There is a fuel pressure regulator on the injector bank between the two rows of cylinders on a 2,5 V6. It looks like a round little device on the lower left side where the fuel line enters.

The middle of this regulator is dented in. Some people say you can dent this in some more to boost the file line pressure so that it pushes more through the injectors. Is this true, and is there a downside to this ??
I suppose it could be true. In simplest terms, the pressure regulator is a two-chamber device. The two chambers are separated by an elastomer diaphram. One chamber is the fuel chamber. It has an inlet, an outlet and a bypass or return line controlled by a valve on the end of the diaphram. The bottom chamber is the vacuum and spring chamber.

When no or little vacuum is applied to this chamber (e.g. WOT), the diaphram has both 1-atm of air pressure and the spring to push it upward, which closes the bypass valve and forces all the fuel entering from the pump to exit to the fuel rail, increasing rail pressure and volume.

When the bottom chamber is evacuated (e.g. at idle), the diaphram falls due to fuel pressure and opens the bypass line, allowing fuel to return back to the fuel tank through the return lines. This reduces the rail pressure.

By deforming the bottom chamber, you might "pre-load" this spring more, causing a nominal increase in fuel pressure. Personally, I'd probably recommend an aftermarket adjustable regulator instead of deforming the OEM one. Once you've bent that chamber in, you can't really unbend it again to reduce the F/P if you go too far or experience driveability issues etc.

Secondly, can a clogged petrol filter make a preformance difference ??
Depending on how clogged it is, sure. It'd have to be pretty badly clogged, but it could happen.
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