Why Return Fuel Setup on High Horsepower

[texwill]

and after seven pages there is smoke coming out of my ears but I learned.

[ritfordprobe]

I can sum it up really easily:

You don't need a return system really, if you go to a standalone. The reason being, you can control the injectors at all rpm's and kPa's, so you can have HUGE injectors and have the pulse width be very low at idle, so the car idles right, and then crank them open at high rpm, so even with the lower fuel pressure due to boost, you can still flow enough fuel through huge injectors.

You can not do this with the stock pcm, because if you just throw huge injectors on, your car won't idle. You can't even cheat huge injectors with an AFC, becasue it won't let you pull enough fuel out.

Solution, get a return line. Its the only way for big injectors on the stock computer, and its the better way for big injectors on a standalone, because you don't have to run them as hard. The light at the end of the awesome return line tunnel is that if you dump the fuel back into the canister (the spoolboy mod), it also makes sure the canister is always full of fuel, and keeps the pump happy. Return systems = yay.

--mark

[teufelhounden91]

BOOM SUCKA!!!!

[gottasrt4]

IMO, this's gotta be one of the most informative threads I've read....I gotta admit, I did notice that when I installed my walbro.....accelleration was MUCH smoother!!! I'm still runn'n stock turbo and stock injejctors, but push'n somewhere 'round 280whp / 320wtq with support'n mods (I had two HUGE exhaust leaks that I've fixed since my last dyno).

now, I'm pretty new to bOOsted cars my damn self, so since this thread's answered it's original question and then some, I wanna introduce another: what does the FPR do?? now, it would seem obvious by it's name, but after learn'n that the fuel pump opens via voltage sent from the ECU, I'm not too sure. but my guess is that the FPR tells the fuel pump how much to push.....how close am I!?

also, would this turn out to be a good supporting mod, kinda like the walbro and return line?? thanks!!!!

[nutz]

ok, a fpr will alow you to adjust the fuel pressure, the computer will control the pulse with of the injectors (they are either open or closed for a period of MS) by turning down the stock fuel pressure (58 psi) this allows you to put a larger injector in and still have the tune be very close to stock, NOW with a rising rate fpr it will add 1 psi of fuel pressure for every psi of boost, this will alow you to take advantage of your now larger injectors and run a richer mix in boost (allowing you to run more boost). this works well for what it was intended for (converting N/A cars to forced induction) what it does not account for is the extreame rich mix in boost that a forced induction car will experiance under boost, to cope with this you will need a fuel computer (afc neo or similar) to pull pulse width from the from the computer at the lower boost levels.

the mechanical reason for a fpr/rl is to ballance out changes in pressure that occure when the injectors are held open for long periods of time for short intervuls (most cars a dampener will work but turbo/super charged cars use very large injectors)this quick opening of the injectors will make the fuel pressure to drop and intern lean out the engine under load (that spells boom). also it will cool off you pump for life span and make it run quieter (thas why you see em on luxery cars).

[nutz]

Quote: Originally Posted by gottasrt4

IMO, this's gotta be one of the most informative threads I've read....I gotta admit, I did notice that when I installed my walbro.....accelleration was MUCH smoother!!! I'm still runn'n stock turbo and stock injejctors, but push'n somewhere 'round 280whp / 320wtq with support'n mods (I had two HUGE exhaust leaks that I've fixed since my last dyno).

now, I'm pretty new to bOOsted cars my damn self, so since this thread's answered it's original question and then some, I wanna introduce another: what does the FPR do?? now, it would seem obvious by it's name, but after learn'n that the fuel pump opens via voltage sent from the ECU, I'm not too sure. but my guess is that the FPR tells the fuel pump how much to push.....how close am I!?

also, would this turn out to be a good supporting mod, kinda like the walbro and return line?? thanks!!!!

the fpr limits the pressure to a static rate, this allows the "tuner" to know how long to open the injector for to get the approprite amount of fuel in the combustion chamber (for correct A/F ratio) this makes tuning a somewhat simple task for the "tuner". without a fpr it would be imposible to tune a car



pulse with x fuel pressure x injector flow rate= the amount of fuel entering the engine
]

the fuel pump is always pumping at 100% (yes their are a couple of exceptions)

the injectors are either 100% open or 100% closed, the mesurment of fuel is from how long they are kept open "pulse with"

a fuel pressure regulator stabilises the fuel pressure, if the psi drops it will compensate by raising the pressure untill it reaches the set limit, and vise versa

a return line allows your pump to push more volume and keep it on demand, this "almost" eliminates any pressure variations at the injector by shortening the distance of supply "this makes the tank closer"


a 1:1 fpr or "rising rate" FPR raises the fuel pressure for every psi of boost it raises, this will compensate "partialy" for boost (this is not a tuning device and has pit falls for turbo cars)

[gottasrt4]

niiiiiiiiiiiiice, it will never cease to amaze me what knowledge can accomplish!!!

WOW, I never knew the injectors had such a static flow rate!!! I just assumed they'd be dynamic...same with the fuel pump.....iiiiiiiinteresting!!!!

but that leads to another question....that kinda makes it sound like you need the AFC if you're gonna put an aftermarket FPR in your car, would that be correct?? wait, that wouldn't be right, would it?! stage 3 comes with a new FPR........so could you install it without risk of running pig rich during boost?? or is THAT what you need the AFC for...so you don't run pig rich DURING boost!?

WOW, gotta love that LEARN'N feel'n!!!

[nutz]

Quote: Originally Posted by gottasrt4

niiiiiiiiiiiiice, it will never cease to amaze me what knowledge can accomplish!!!

WOW, I never knew the injectors had such a static flow rate!!! I just assumed they'd be dynamic...same with the fuel pump.....iiiiiiiinteresting!!!!

but that leads to another question....that kinda makes it sound like you need the AFC if you're gonna put an aftermarket FPR in your car, would that be correct?? wait, that wouldn't be right, would it?! stage 3 comes with a new FPR........so could you install it without risk of running pig rich during boost?? or is THAT what you need the AFC for...so you don't run pig rich DURING boost!?

WOW, gotta love that LEARN'N feel'n!!!

stage 3 is a completely tuned set up, PW and pressure is calculated into the tune

using a FPR/RL and AFC is used to compensate for what the stock (stg1/2/3) computer can not compensate for...taking it to the next level

in most cases a fuel computer (can only pull fuel) should be fine with larger injectors for more boost, the RL is used when the FPR can not compensate for fluctuations in FP (this usualy will lean out the motor under heavy load) that happen for a short period when going WOT.

[gottasrt4]

niiiiiiiiiiiiiiiiiice - I'm goin' for 300whp on the stock turbo this summer, so I'll DEFINITELY include those!!! thanks!!!