boost and fuel

[Guest]

hay guys, got a version 7 sti. im putting on a 2 1/2 inch downpipe and 3 inch exhaust after that. also running a k+n panel filter. im going to split the rails, run a sard rising rate fuel reg and walbro fuel pump. apart from adjustys etc everything else is standard. what i need to know is how much pressure should i run on the reg and what would i be able to turn the boost up too whilst keeping everything 'safe'. any help much appreciated. cheers.

[xsvpwr]

if you are putting a 2 1/2 inch down pipe on, whats the point in making the rest of the exhaust 3 inches?

[Pappu1]

43-44psi static pressure at idle with vac hose off

thats whats been done on most cars running stock ecu map

if u got link or something else then whatever ur tuner wants to set to as will be mapped accordingly

[czar loc]

So All Subaru Fuel regs work at same pressure? just asking cos i want to do a split setup but have four differrent sets of rails + Regs

[Wiretap]

All Subaru regs run the same pressure but you should use a matching pair because they don't all flow the same.

Also, don't use rising rate regs, they mess up the fuelling. Use a standard linear regulator or even a factory one as I do.

[Guest]

to the exhaust part, its just what i have lying around. question is why not use it? and whats the performance difference between a linear and rising rate fuel reg?

[Wiretap]

 XQU5ME said:

to the exhaust part, its just what i have lying around. question is why not use it? and whats the performance difference between a linear and rising rate fuel reg?

There is no 'performance difference' between the regulators. A linear regulator will raise the fuel pressure 1psi for every 1psi of manifold pressure increase. This keeps the fuel pressure constant relative to manifold pressure, ensuring consistent fuel delivery. A rising rate regulator will, say at 0psi of boost, raise it 1psi for that 1psi increase to 1psi-boost. But at 10psi-boost to 11psi-boost it might raise it 3psi... This will not work with your factory ECU even with a re-tune

[Guest]

mine is 1.7:1 what problems does that cause? running rich?

Tomei, sard and aem do 1:1 and chinese ones are on tm also...

[Wiretap]

 evowrx said:

recommendations on fuel reg? it doesnt say on sards site what the rising rate is on theres.

mine is 1.7:1 what problems does that cause? running rich?

Running lean in vacuum and rich on boost assuming you set it up with the vacuum line disconnected.

My recommendations for FPR are either a factory one, or any reputable brand aftermarket one which is 1:1 rate.

[WRXONP]

1.7:1 thats crazy

to explain a little easier

if static pressure is set to 45 (nice easy number)

with 20 psi boost on a 1:1 reg you will have 65 psi fuel pressure on WOT

with your 1.7:1 reg you will be running a crazy 79 psi fuel pressure - that shit cray

[Guest]

yea boss i did the math too just wondered what it would be doing.

i thought it was 1:1 i just did some research after i read this. ive always run sard which are 1:1. ive put one on my growing shopping list.

[WRXONP]

yea - allot of people sell linear rate regs (1:1) on trademe listed as rising rate - because they think that since fuel pressure goes up it must be rising rate - just a marketing scheme really

not sure why or who would actually want a rising rate reg -

[Marky]

Probably made sense once upon a time before cheap s-afc's or reflashes came along, if you're turboing your honda or n/a whatever it would have been a cheap way to get a bunch of fuel dumped in on boost to try and avoid it blowing up

Least that's the logic I imagine was used

Strikes me as about as intelligent as chucking a one-way valve on the fpr vacuum hose as a cheap way to lean off something which is too rich on boost

[WRXONP]

LOL - that reminds me

i was flicking through a fast fours one day a fair while back and it was the top 10 tuning tips

i clearly remember one was "we reccomend fitting a one way valve onto the FPR line on RB20 and RB25dets as they run too rich and the one way valve will stop this"

i was like WHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAT