# Fuel injector flow rate formula help... **URL:** \ **Category:** Shift518 Automotive\ **Created:** [November 29, 2011, 1:58pm UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525 "2011-11-29T13:58:22Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![KrazyKid](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/krazykid/32/6371_2.png) [@KrazyKid](https://forums.speedlife.net/u/KrazyKid)\ **Post date:** [November 29, 2011, 1:58pm UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/1 "2011-11-29T13:58:22Z")
I have been working on making an excel sheet to calculate injector flow rates, to get an adequate size design for a surge tank. I found this guys thread… [http://forums.nasioc.com/forums/showpost.php?p=21443184&postcount=20](http://forums.nasioc.com/forums/showpost.php?p=21443184&postcount=20) and if you pump his numbers into the calculator RC Fuel injectors site (with the formulas which I used in my excel sheet) they dont match. The part about adding 10Psi to his 270cc injectors to be exact. he says they are now “332.79cc’s”, yet RC’s site & math say its only 299.76CC. Infact to hit his flow rate assumption it needs 22psi more pressure as per RC’s site. Now he is taking the flow at base pressure and finding how many CC’s it flows at 1psi. Taking that number and multiplying it by the pressure increase to get the “additional flow” from that pressure increase. OR 270CC @ 43psi = 6.279CC per 1psi then 6.279CC \* 10 = 62.79CC more flow from the injector or **332.79CC total** BUT as per RC Injectors math its nowhere near that. (I assume it takes in account it cant be a static 1:1 ratio) [http://www.rceng.com/technical.aspx](http://www.rceng.com/technical.aspx) 50/43=1.162, then the square root of 1.162 = 1.110, then that X the old flow rate (270) or the new injector flow rate of **299.76CC total.** Based on RC’s figures: 299.76cc / 50 psi = 5.995 CC per PSI 270cc / 43 psi = 6.279 CC per PSI /\ not a 1:1 ratio PSI:CC like that first guy assumed. So who is right? :pop I assume since the orifice at the end of the injector doesn’t change, it throws off the theory. ---
**Author:** ![jdaniels](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jdaniels/32/6399_2.png) [@jdaniels](https://forums.speedlife.net/u/jdaniels)\ **Post date:** [November 29, 2011, 2:15pm UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/2 "2011-11-29T14:15:58Z")
**{Square Root (New base pressure/Old base pressure)} x Old Flow rate = New flow rate** ---
**Author:** ![jdaniels](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/jdaniels/32/6399_2.png) [@jdaniels](https://forums.speedlife.net/u/jdaniels)\ **Post date:** [November 29, 2011, 2:19pm UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/3 "2011-11-29T14:19:05Z")
Oh, and he’s wrong. ---
**Author:** ![Alpine](https://avatars.discourse-cdn.com/v4/letter/a/4da419/32.png) [@Alpine](https://forums.speedlife.net/u/Alpine)\ **Post date:** [November 29, 2011, 2:23pm UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/4 "2011-11-29T14:23:05Z")
_Looks for spreadsheet_ _Unable to locate spreadsheet_ _Trolls thread anyway_ ---
**Author:** ![KrazyKid](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/krazykid/32/6371_2.png) [@KrazyKid](https://forums.speedlife.net/u/KrazyKid)\ **Post date:** [November 30, 2011, 6:45am UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/5 "2011-11-30T06:45:28Z")
thanks JD. I thought that was the right one and that’s what I was using on my excel sheet. See attached for sheet. download and change .txt to xlsx :number1 ---
**Author:** ![Johawk](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/johawk/32/6284_2.png) [@Johawk](https://forums.speedlife.net/u/Johawk)\ **Post date:** [December 5, 2011, 8:20am UTC](https://forums.speedlife.net/t/fuel-injector-flow-rate-formula-help/261525/6 "2011-12-05T08:20:02Z")
JD is the man when it comes to injector flow rates. I PM him direct! LoL