Which Turbo should i go with!? HELP! 18G?

The true idea behind AFPR is keeping the fuel pressure steady during off-boost conditions and raising it in 1:1 ratio (= 1 psi of fuel pressure per 1 psi of boost) during on-boost conditions - which means that the FPR needs to have adequate flow capabilities if it's supposed to work with large fuel pumps. The stock FPR (even if combined with the CommandFlo) suffers from very small orifice that is not able to provide enough flow to channel the excess of unused fuel back to the fuel tank in sufficient manner, which leads to overruning the FPR during off-boost and further difficulties with tuning since the fuel pressure constantly fluctuates with the voltage supplied to the fuel pump during accessories use.
As for the reduction or increase of fuel pressure, it's a bit more complicated and that's where the S-AFC comes to play, since most aftermarket injectors are rated and designed to work with 43.5 psi, while the stock base fuel pressure of 1G M/T DSMs is 36.3 psi.
In a perfect world, the fuel curve would be shaped very close to stock with minor adjustments improving throttle responce while the S-AFC settings very close to 0 across the board. While moving the entire fuel curve up and down is achieved by increasing or reducing the fuel pressure, people with big fuel pumps have no choice but compensate for the lack of AFPR by their S-AFC settings that end up looking like an ass (going from -20% at low RPM to 0 at high RPM) which consequently leads to knock issues after every shift since the timing curve is severely affected.
AFPR simply allows tighter S-AFC settings while moving them close to 0 to avoid excessive timing advance and consequent knock issues at lower RPM.

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In my opinion, running any bigger-than-stock fuel pump without AFPR is a half-assed fuel system modification that may cauise problems when it comes to tuning.
http://www.dsmtalk.com/forums/showt...0818#post950818
Some people claim that one can successfully run the Walbro 190 without AFPR. Then their IPW maps are stretched to hell due to their S-AFC settings jumping across 20% across the board just to compensate for a fuel pressure curve that looks like an ass and changes any time one turns his headlights or turn signals on. Then they slap on a set of 660cc's and run the bitch at -30% S-AFC settings with timing that looks like it came straight from Chevy 350 while they wonder where the "phantom knock" came from.

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One can see people running their S-AFCs at -20% to maintain an acceptable A/F ratio while the IPW table, timing and fuel pressure curves look like an ass and the car knocks like a bitch (and they blame it on "phantom knock"). Maintaining a proper fuel pressure and timing curves are the key to any successful tuning - which is impossible to achieve without AFPR if bigger than stock fuel pump and fuel injectors are utilized.

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AFPR is extremely useful for two things: 1) provide efficient fuel return and 2) move the entire fuel curve up and down as needed in order to keep the timing under control when large injectors and S-AFC are used. For example, if the stock fuel curve was "perfect", one would have all RPM point settings exactly the same and their percentage set just bellow the threshold of fuel cut (on the negative side of the S-AFC) while adjusting the actual A/F ratio only by altering the fuel pressure with the AFPR. That's actually a good idea of initial setting - as opossed to establishing the base fuel pressure first.

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K_Mans_TSI said:

better times through more accurate/better tuning.

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K_Mans_TSI said:

they all just claim they have cams

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