injector size Options

[xian 1g]

Hey,
I apologize for the plaque of questions cluttering the board, but its relatively hard to do a search while I'm driving and read an extensive write up... something about keeping the eyes on the road is atleast better than driving with no hands.


anyways...

what size injectors should i run with a fp3065? rewired supra fuel pump. fmic, etc....

eric, you mentioned something about the supra being maxed out with 750's at 43psi? Looking to hit tens.

thanks in advance...

[zach]

First what is your desired flywheel hp?
and at what psi of boost will this be attained at.
are you batch firing of sequential.
take total hp multiply by the brake specific fuel comsumption of your motor. ( most claim o.62 on 2 liter turbo. an divide that by the number of injectors to be used times the max duty cycle, that will get you lbs/hr for injector. multply this number to by 10.5 to convert to cc's

example: 500hp x .62 =310. divide by 4x.80 =96.875lbs/hr
and maximum 80% injector duty multiply by 10.5 to get cc's wich would equate to 1017 cc injector at 43.5 psi
this injector is way to big, because you will not be making max hp at only 43.5 psi instead...

the more boost the more fuel
example 25 psi of boost, then fpr 1psi boost = 1 more psi of fuel.
you will now be running 68.5 psi fuel pressure

I love math (remember this 80% duty cycle, it should not be breached or possible failure of injector could result)

since you will be using 68.5 psi instead or the 43.5 psi, you take 68.5 and divide by 43.5 to get 1.5747
you then take the square root of this number, which would be 1.25487 and multiply this by the original injector fuel flow of 1017cc of fuel and you would be pushing 1276 cc's of fuel into this beast.
which is way to much fuel.. so lets go backwards and take away 25 psi by dividing our 1017 cc by 1.25487 and we would then get 810 cc's


so size 810cc's @43.5 psi is what is required to support our 500hp motor runing 25lbls of boost and 68.5 psi of fuel pressure.

now... batch or sequential?
by the numbers 810 will work for both sequential an batch
sequential...810 at the minimum, throw in a set of 1000cc injectors, tune your aem ems, call it a day.
batch... you can probably get a way with a little smaller ie. 750s with out a hint of a lean condition problem. but i would get the 800 + injectors just to be safe

next question.

do you have enough fuel pump.
in our example you need a pump that will support 310lbs/hr of fuel at almost 70psi
make sure its there.