well i plan to do the 8-injector setup. ok so i plan to get 252cc and 415 accel injectors which puts me at 670cc injectors.
primary rail 252cc
secondary 415cc
so i was trying to use corbins formulas again, and if i input 350x0.525x10.5/4= 482.34
then i do 482.34/0.85=567.46
ok, so now i have a injector size of 567 which it says i can use, but i plan on running the 8-injector setup which equal 670cc total.
so this is all correct so far right?
what im trying to figure out is the rest, to find max fuel pressure and idle/static.
do i use the same "fuel pressure equation" to still find what fuel pressure to run this injector? i thought it was only if you use a smaller injector?
the fuel pressure equation is ((approximate injector size)sqaure times p rated)+ p manifold and for my setup this equals (567.46/667)sqaure that and times it by 43.5)+max boost which should give me max fuel pressure right?
also maybe i miss this but for max boost in this formula do you just enter any number? if not how do i figure it out?
thanks for the input
Michael 99gs
HRC Stage 2 @12psi
Stage 3 process begins gathering parts for rebuild
2GNT Member #32

http://www.dreamwater.net/purplebeast

>well i plan to do the 8-injector setup. ok so i plan to get
>252cc and 415 accel injectors which puts me at 670cc
>injectors.
>primary rail 252cc
>secondary 415cc
>so i was trying to use corbins formulas again, and if i input
>350x0.525x10.5/4= 482.34
>then i do 482.34/0.85=567.46
>ok, so now i have a injector size of 567 which it says i can
>use, but i plan on running the 8-injector setup which equal
>670cc total.
>so this is all correct so far right?

Yes.

>what im trying to figure out is the rest, to find max fuel
>pressure and idle/static.
>do i use the same "fuel pressure equation" to still find what
>fuel pressure to run this injector? i thought it was only if
>you use a smaller injector?

I'm not sure what the EIC can control, so I don't know this one. sorry.

>the fuel pressure equation is ((approximate injector
>size)sqaure times p rated)+ p manifold and for my setup this
>equals (567.46/667)sqaure that and times it by 43.5)+max boost
>which should give me max fuel pressure right?

Yes.

>also maybe i miss this but for max boost in this formula do
>you just enter any number?

To choose a boost level, you must match your chosen power. It appears as though you plan to run about 350 HP. This should equate to somewhere around 15psi. You might have a better guess than I do on that number, but from previous data on our cars, I think it should be in that ballpark.

99GS MT | Star Stage 2 | GC coilovers | HurriganeGS tie bars | Tokico Illuminas | 17x7 Enkei RS5 | Baer track brakes |+

thanks for the input.
anyone else care to share some light on me?
Michael 99gs
HRC Stage 2 @12psi
Stage 3 process begins gathering parts for rebuild
2GNT Member #32

http://www.dreamwater.net/purplebeast

You don't really need to do much calculating for the 8 injector setup. You use a 1:1 reg, so your max fuel pressure isn't very meaningful. Fuel pressure increasesin the same proportion as intake manifold pressure. So you have the same fuel capability at 1 psi as 15 psi.

You set your static fuel pressure to give you good driveability. If you use 252's then you'll have to set it below stock levels. I set my fuel pressure really low (30-something static and 26 psi under vacuum). That leaves me a little lean (~5%) right before the secondaries kick in. I think that makes for a good transition from 4 injector duty to 8. Once you find a fuel pressure that gives you good driveablilty, then you forget about the FPR. Every adjustment after that is electronic.

The main reasons to use the formulas with an 8 injector setup are to estimate a static pressure and to estimate a max power capability. Chances are, that you'll be running low fuel pressures, so you can assume the pump can handle it.

Keep in mind that as you adjust the static fuel pressure to get good driveabilty, you adjust the fuel pressure for both sets of injectors. If you drop your fuel pressure to make your primary 252's give you less fuel, then your secondary injectors will give proportionately less fuel too. For example:

If I'm running 34 psi of differential fuel pressure on (8) 252's, then each injector can supply 223 cc/min. Thats a capability of only 446 cc/min per cylinder. I'll have to upgrade my secondary injectors whenever I get a real engine.

Corbin

'95 ESI-T
HRC+FMIC+ETC...



Gimme fuel...Gimme fire...Gimme that which I desire

"If I'm running 34 psi of differential fuel pressure on (8) 252's, then each injector can supply 223 cc/min"

sounds dum, but how do we figure out what each injector can supply _____cc/min?
and to find differential fuel pressure do i just take max fuel pressure and mins it from max boost? if not how do i?

thanks
Michael 99gs
HRC Stage 2 @12psi
Stage 3 process begins gathering parts for rebuild
2GNT Member #32

http://www.dreamwater.net/purplebeast

>"If I'm running 34 psi of differential fuel pressure on (8)
>252's, then each injector can supply 223 cc/min"
>
>sounds dum, but how do we figure out what each injector can
>supply _____cc/min?

You only need to find out two major things really in terms of its relation to fuel injector sizing. One, what type of fuel capabilities you'll have at max boost, and two, what your fuel pressure will be at idle. For max boost, you merely add a primary rail and a secondary rail's fuel injector. (Ex. 235 + 440 = 675cc's) Therefore, with the above example, you have the capabilites for the fuel equations, of a fuel injector of 675cc's for figuring out the equation when basing that on 4 injectors. (Otherwise, you can use the same equation, add up the total injectors output and divide by eight(8), but don't worry about that)

Secondly, the only concern for idle is the same concerns of anyone else with 4 injectors. If you have anything smaller than 30#'s or so, you should be able to drop the fuel pressure to as low as necessary to get good fuel trims. That varies, but the whole advantage to the 8 injector setup is to avoid idle issues with larger injectors. I recommend something small. (~235-300 obviously)

>and to find differential fuel pressure do i just take max
>fuel pressure and mins it from max boost?

Again, don't worry about this. (as Corbin alluded to) Just use a 1:1 FPR after you have your static fuel pressure set. The EIC will control how much fuel you need. It's all computerized though through fixing your injector pulsewidth. No more mechanzed mayhem through altering fuel pressures!! yay!

>if not how do i?

You'll do ALL your tuning through the EIC fuel mapping device.

_____________________________________
Jason ESi-T

04' BMW 325Ci
91' Nissan 240SX
98' Eagle Talon ESi (sold)