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...

[wortdog]

Or, you could just go here and play around to your heart's content:

http://www.rceng.com/technical.htm#WORKSHEET

0.62 is WAAAY conservative for race gas IMHO. According to all of the worksheets, running my 6 38lb/hr injectors at 46 psi and 100% duty cycle with an assumed crank HP of around 450 (from a 112 mph trap speed in a 3800lb car) results in a BSFC of .52 or so. Its actually probably more around 0.51, as I'm not running my injectors at static quite yet. The wideband shows between 12.5:1 and 12.8:1 AFR on the run.

Also, the part about taking the square root of the fuel pressure doesn't make any sense. The whole point of the fuel pressure rising with boost is to maintain a set pressure differential (in this case, 43.5 psi, which is what most injectors are rated at) across the injector, such that opening the injector for a given pulsewidth will always result in the same amount of fuel flowing across the injector. If you want to change your base fuel pressure, you can divide the square roots of the pressures and multiply that times the injector flow to get your flow at the new pressure, like so:

Sqr(45psi) * 450cc / Sqr(43.5psi) = 457.69 cc