Ni5mo180SX

Ok, two scenario. Which one would flow the most fuel on an 88 T2.


A) 550cc injectors x 4 using Walbro 255 fuel pump and adj. FPR set at 40psi which is when the Walbro flows 255lph.

B) 550cc x 2 and 680ccx2 using a Walbro 255 at stock fuel pressure.

Let me know your opinions. Thanks.

maxcooper

The pump doesn't matter as long as it can maintain the regulator pressure at maximum injector flow.

550x4 at 40 psi and 100% duty cycle = 2110 cc/min

550/680 at 100% duty cycle will need to be at this pressure to match that flow = 32 psi

I would guess that the stock pressure is higher than 32 psi (probably more like 37 psi), so the 550/680 setup will flow more.

Here's a web page I made to play with the values:
http://208.55.168.23/rx7/how-to/fuel_system/calcs.html

-Max

Scott 89t2

stock is higher then 40 under boost....

maxcooper

The thing that matters for injector flow is what I call the effective pressure, which is fuel rail pressure minus boost pressure. The injectors will flow according to the pressure differential across the injector, and that that is what the effective pressure is since the injectors squirt fuel into the pressurized manifold under boost. The regulator has some base pressure, which is the pressure you'd get with the manifold reference pressure signal (vacuum hose) disconnected. For standard regulators like this, the base pressure is the effective pressure as the regulator will raise pressure under boost and lower pressure under vacuum to keep the effective pressure constant. If your fuel pressure gauge reads 47 psi at 10 psi of boost, the effective pressure is 37 psi. I would expect that to be quite near the effective pressure on the T2.

-Max

maxcooper

Also remember that you need to have something to control the injectors to have the car run right and make maximum power. You could install four 1680 cc/min injectors, for instance, and that would be enough injector for 630 RWHP at 80% duty cycle and 37 psi effective pressure. But, I would be surprised if the car would even run with injectors that large without addressing the control system (ECU) since it would be incredibly rich. The ECU knows nothing about the injector sizes, so it won't just adapt if you install different injectors.

Another issue to consider is if the ECU stages the injectors (primaries only for low load/RPM, then all the injectors for higher load/RPM), the ratio of primary to secondary sizes may need to be the same as stock for it to make the transition properly. This is a big issue on the FD, and you can't run bigger secondaries very will with the stock ECU and a piggy-back computer, because it will always screw up at the transition. The transition isn't simply RPM-based, so you can't just adjust the injector signal at the changeover RPM to make it work right. The transition is based on load and RPM, so an RPM-based adjustment is ineffective. I am not sure how the FC stages its injectors, or if it even does any staging at all, but it would be wise to find out before you change the primary:secondary ratio.

-Max