Is 47 For Fuel Pressure to high

red82gt · 05-29-2001, 07:23 PM

With those injectors you've got enough fuel for ~400 N/A horsepower!
You'd be better off with the 19 lb'ers. Since you've got the Bullet mass air meter I would knok the fuel pressure down to about 30 psi, even that will support ~320hp.

Here's my logic:
24lb inj. X8 inj.=192lbs
N/A cars need ~.5lbs of fuel/hp so: 192lbs/(0.5lbs/hp)=384 hp @40 psi fuel pressure.

to figure out the flow at 47 psi. take the square root of the new fuel pressure and divide it by the square root of the stock fuel pressure.
(47^1/2)/(40^1/2)=1.08
take this number and multiply it by the max number of hp at the stock pressure so
1.08X384hp=416hp! Your injectors won't be able to flow at capacity all the time so this much fuel pressure will still support 400hp.

So at 30psi: (30^1/2)/(40^1/2)=0.87
0.87X384hp=332hp.

In short, set it to 30 psi, anything more and you'll be wasting fuel!

------------------
GT-40 heads (ported, polished, + milled), B303 cam, 1.7rr's, JE pistons, Offy intake, Carter AFB 625cfm carb, Flowtech 1 5/8" shortys, Flowtech X-pipe, MAC Flowpath exhaust, MAC pulleys, 373's, subframes, Eibachs+Tokicos, B&M ripper, FMS Clutch, Zoom Quadrant+cable, 17" CSA Ultra rims, 235/45ZR17 Yokohama AVS S4's, MSD 6A ignition+coil, FMS 9mm wires, Carbed, Naturally Aspirated, and Nasty!

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05-29-2001, 07:23 PM	#4
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,514	With those injectors you've got enough fuel for ~400 N/A horsepower! You'd be better off with the 19 lb'ers. Since you've got the Bullet mass air meter I would knok the fuel pressure down to about 30 psi, even that will support ~320hp. Here's my logic: 24lb inj. X8 inj.=192lbs N/A cars need ~.5lbs of fuel/hp so: 192lbs/(0.5lbs/hp)=384 hp @40 psi fuel pressure. to figure out the flow at 47 psi. take the square root of the new fuel pressure and divide it by the square root of the stock fuel pressure. (47^1/2)/(40^1/2)=1.08 take this number and multiply it by the max number of hp at the stock pressure so 1.08X384hp=416hp! Your injectors won't be able to flow at capacity all the time so this much fuel pressure will still support 400hp. So at 30psi: (30^1/2)/(40^1/2)=0.87 0.87X384hp=332hp. In short, set it to 30 psi, anything more and you'll be wasting fuel! ------------------ GT-40 heads (ported, polished, + milled), B303 cam, 1.7rr's, JE pistons, Offy intake, Carter AFB 625cfm carb, Flowtech 1 5/8" shortys, Flowtech X-pipe, MAC Flowpath exhaust, MAC pulleys, 373's, subframes, Eibachs+Tokicos, B&M ripper, FMS Clutch, Zoom Quadrant+cable, 17" CSA Ultra rims, 235/45ZR17 Yokohama AVS S4's, MSD 6A ignition+coil, FMS 9mm wires, Carbed, Naturally Aspirated, and Nasty!