What are the ways to change A/F ratios?

[Vovan]

?

[BOOSTD]

Change the voltage that the ECU sees coming from the air flow meter. Apexi make alot of Air flow converters

[Vovan]

that's one... is there a stock fuel pressure regulator? can it (pressure) be adjusted?

[Steve]

Best way to do that is a fuel pressure reg. Can be had for under $200AUD from greenline for a nismo item.

this is a pretty bodgey fix, as you may need the fuel up top, or under full boost. But, unless you can tune the car, you will get the extra fuel across the board, so run very rich which can cause major problems in itself.

I have heard of people 'adjusting' the stock fuel pressure regulator with a pair of pliers, which isnt ideal, but you still need to tune the car to the new fuel pressure

It also appears that upgrading to a larger fuel pump will cause mixtures to run a bit richer, as a few guys here have noticed when upgrading. Not sure why though, as in theory the fuel press reg should not be allowing this.

[Vovan]

where is the stock fuel regulator located?

[Steve]

At the front of the fuel rail.