I just did some calculations on injector size and the flow rate of the walbro 255hp fuel pump. my results are cause for alarm. i hope i'm wrong.

it seems to be common practice to get a 12:1 fmu and raise fuel pressure as high as 110 psi in hopes of increasing flow through the stock injectors. this would work fine if the fuel pump had the same flow rate at all pressures, but it doesn't. as you increase the fuel pressure, the pump flows less GPH (gallons per hour).

the walbro 255hp is capable of the following flow rates:

80 psi: 43 GPH, 2714 cc/min
90 psi: 35 GPH, 2209 cc/min
100 psi: 27 GPH, 1704 cc/min
110 psi: 15 GPH, 946 cc/min

15 GPH converts to 946 cc/min.
that breaks down to only 236 cc/min for each injector!

theoretically, your stock 234cc/min injectors should flow 374cc/min at 110 psi. this number seems to be severly limited by the fuel pumps ability to keep up the flow at that pressure.

this data suggests that we should not expect the walbro 255hp to produce sufficient flow at incredible pressures. if you do, you will run lean and we all know what that means. i would think 90 psi is a reasonable MAXIMUM fuel pressure. that pressure would be capable of feeding 4 injectors at 568 cc/min each. this is enough to support about 285-290 hp. lower fuel pressures would also reduce the risk of injector lock-up. 70-80 psi would be an even better pressure range to operate in.

the trick is choosing the right size injector to flow enough without needing extremely high fuel pressures, yet be small enough to either sneak by the stock ECU or be managable by a S-AFC. I know injectors are a little pricey, but after reading this, do you still want to run your stock injectors at 100 psi or higher?

http://www.rceng.com/

http://www.vfaq.com/pump-Walbros.html