platinum00

i need to swap in my 550cc injectors but im not getting tunned on these till next week.

im thinking i can do this to get me by

run them at 30psi instead of 43.5 psi. should be close enough

30/43.5 = .689655 , square root of that = .830455 x 550 = 456.8cc

these number are all rounded.

anyway. will i hurt the injectors if i run them at a lower rail pressure.

platinum.

Cyphear

No you should be fine with that setup. You might need to play around a little bit with the fuel pressure since different size injectors have different outputs at different duty cycles. If anything you will need to give it a little more fuel pressure than 30. Why dont you run (450/550)43.5 psi anyway? which would be 36 psi. I'd run 36 psi and see what happens, and increase fuel pressure if necessary.

platinum00

43.5 is what most injectors ar tested at.

that's why i did the correction from there.

platinum.

Cyphear

No what im saying is why dont you do the math 450/550*43.5 = 36 psi. so why would you do 30 psi. Do you understand my math/logic? i dont understand yours. (i'm not saying its wrong, i just dont get it. Why would you take the square root of 30/43.5? then multiply that by 550?

platinum00

i understand what your sayin now'

i just used the formula on rc injectors website

look at example 1 @ http://www.rceng.com/technical.htm

let me know if i should still do it your way

it makes sense both way to me.

platinum.

kpt4321

I can't tell you what pressure to run them at, becaue I don't know what pressure you are at now. You can't use 43.5 psi as your basis, because that might not be what pressure you are at now.

You need to set it up so that the square root of (new pressure/current pressure) is equal to about 0.82.

If you want, post up the new numbers (or even better, PM me) and I can check them for you before you drive the car, to be safe.

kpt4321

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cyphear &raquo;</TD></TR><TR><TD CLASS="quote">No what im saying is why dont you do the math 450/550*43.5 = 36 psi. so why would you do 30 psi. Do you understand my math/logic? i dont understand yours. (i'm not saying its wrong, i just dont get it. Why would you take the square root of 30/43.5? then multiply that by 550?</TD></TR></TABLE>

You have to take the square root, because flow isn't proportional directly to the ratio of the pressures. It's just a property of physics.

platinum00

im running at 43.5 rail pressure right now.

platinum.

kpt4321

Ok. If you are running a base pressure of 43.5 psi, then ~30 psi is what you want to run.

Cyphear

Awesome, keep us updated how it works. I think your way is probably right. but like i said in my first post, you might need to bump it up a little over 30 if it doesn't run because of the "slow" open charactheristics of larger injectors.

platinum00

thanks for the info.

i should be doing this early next week, if not sunday..

ill pst up the results.

platinum.

platinum00

FYI,

i forgot to let you guys know.

this worked great. car ran as it did with 450's



thanks for the input

platinum.

n1_ek

can i do this with 550cc and adjustable FPR and Walbro 255lph?

Cyphear

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ryan819 &raquo;</TD></TR><TR><TD CLASS="quote">can i do this with 550cc and adjustable FPR and Walbro 255lph?</TD></TR></TABLE>

from what to 550's?

Thanks for the update plantinum00.

0xenocron

Wont the decrease in rail pressure promote less than optimal atomization characteristics?

That would worry me