98,Ram,Air

I have a racetronix 255 lph pump with the stock fuel lines, rails, regulator and injectors. I wanted to go from a 135 to a 200 shot of dry N2O but the injectors won't handle it. A guy from school says on fords they close off the return line and then the pressure bosts to the injectors giving more fuel. Can the same thing be rigged up on the LS1 system? If the pressure is boosted to like 65 psi would that squeeze more fuel through the injector when it pulses? This would have to be at full throttle of course. I don't want to spray fuel through the intake. I believe they are built to flow air not liquid( I am afraid of puddling).

fast98

iTrader: (16)

your 98 doesn't have a return line, and in theory that does work on other cars equipped with a return line but if u completely block the return line u will dead head the pump which is bad and vastly shortens its life

white2001s10

iTrader: (4)

https://ls1tech.com/forums/nitrous-oxide/265679-how-does-maf-compensate-dry-shot.html

Increasing pressure works but isn't always the best option.

98,Ram,Air

I read all 9 pages of arguments. This sort of answers my question but not really. If I increase pressure in the fuel system the injector pulse could stay the same and deliver more fuel due to higher pressure.

onfire

iTrader: (17)

Yes, in theory if the pw stays constant, then increased fuel pressure will flow more fuel through the injectors IF THE PUMP WILL FLOW THE VOLUME AT THE HIGHER PRESSURE. Which is not always the case. I would properly size the injectors and pump for your goals.

98,Ram,Air

What about a boost a pump?

white2001s10

iTrader: (4)

He says he already has a good pump, so it should be able to handle increased pressure for short periods and mantain good volume.

Yes, increasing the voltage to the pump will increase volume capability and pressure.

onfire

iTrader: (17)

You need to calculate the increase in pressure needed to flow the fuel through the small injectors first. Then look at the flow curve on a 255 walbro at 12v and see if it will meet the flow....the flow drops drastically at higher pressures which is why I would not rec this. You can also use a boost a pump to increase the voltage to 16v which will increase the flow through the Walbro....do the math first, but I would buy the proper injectors...good luck!

98,Ram,Air

did anyone else read the link above from white2001s10? On the 98's are the injectors at 100% duty cycle at wot? or do they have a default where they goto and no higher? like is the car set to run wot at 85% duty cycle?

Old Geezer

iTrader: (3)

The inj duty cycle is called by the ecm, when the calcs are made, using the various sensor inuts.
The 100% value is not an absolute, occurs only when that amt of fuel is commanded.
The 85% you refer to is a general value used to calculate the size of injectors required for a particular application. It is a common value, in that some inj designs become overheated, inconsistent in pulsewidth, etc, when run at or near static.

jimmyblue

iTrader: (11)

Raising the pressure will result in more fuel delivered at the
same injector pulse width (or dead-open). But how to best get
more pressure, you have to figure out. Larger lines and better
wiring will get rid of hydraulic and electrical losses, without
pushing more fuel at the low end (which you don't need). A
front mounted regulator will make fuel pressure more
consistent and eliminate pressure fade from line flow losses.
But here you'd have to run another line back to the pump. I
wonder sometimes about eliminating the pump-tank short line,
and running the blowoff back from the engine instead (reusing
the original forward feed as the return, and a new fat line
for the new forward feed).

None of this requires getting into the tank, or running higher
(setpoint) pressures. But it should improve the high demand
end fuel pressure. What do you have for fuel pressure readings
at top-end WOT, now?

98,Ram,Air

I am wondering if the ECM has a preset duty cycle which it will run at under wot and no higher. Once I reach the max limit determined by the ECM it doen't matter whether I run a 1000 shot or a 200 shot the ECM will dump the same amount of fuel. What duty cycle is that limit? Is it 100% duty cycle, 85%, 90%? What is the way I find that out? What I am trying to determin is if I run 135 hp. shot will the injectors flow the same if I run a 200 shot. I would like to know that because it will answer my question if I can increase the fuel pressure to increase the amount of fuel pushed through the injector. I do not want to run a 200 hp. dry shot if my injectors will be static.

white2001s10

iTrader: (4)

Once your injectors are at 100% you can only increase fuel flow by increasing the pressure.

If you want to avoid ever running at 100%, then you'll have to get much bigger injectors than stock... something like 42 lb/hr,
and then (important step) have the PCM recalibrated for the larger injectors.

If you don't want to run pig rich with a small dry shot, then install the nozzle far away from the MAF wires. The closer the nozzle, the higher the MAF output will be, and you'll get more added fuel.