I have an NX kit jetted for a 125-shot (57/31). Stock engine, fuel pump, regulator. Using an AutoMeter electric fuel psi gauge.

When the spray hits in 2nd gear at 3000RPM, the fuel psi will drop from the WOT level of 43.5 to about 20 for a second or less, then come back up. I'm pretty sure this is what is causing the .0xx O2 sensor values I was seeing in my logs occasionally when the spray hits. But they would then go back up to high 800s/low 900s, seeming to follow this fuel psi thing.

I'm curious if this could be an artifact of having a T on the schrader valve, one side going to the FP sender, the other to the NX fuel noid. Could the sudden demand of the fuel solenoid opening cause not enough fuel to push against the sender? So, could it be that the fuel psi really is staying at 43.5 but that the sudden hit draws fuel away from the sender?

Or, should it stay the same regardless?

Ideas? Does it just mean my stock fuel pump (2 yrs old, GM-installed under warranty) can't keep up?

 

I say dont take a chance on it....get a new higher volumn intank pump for a 125 shot.

You could jet down to a 75 shot and see what happens to your fuel pressure when you hit it.

 

i say at the very least, get an external pusher..thats what i did.. i monitored my car on the dyno with a wideband 02 , making sure to pay attention to FP(among many other items on the scanner) and mine showed momentary 10-15 psi drop...which doesnt really concern me all that much...
its more a volume issue... and whats coming out to the tailpipe(no cats on my car)..thats important to me... we tuned my car to 12:1 A/F...kind of rich.. but good for the jug

good luck..IMO, tuning becomes critical at 100 shot or above...

 

Well, it's not dipping with the 75HP jets. But I'm still getting knock retard, albeit less.

I might try different plugs. I have Autolite 104s gapped at .040". Maybe I'll try the 103s...

 

NGK's

TR6's

 

[QUOTE]Originally posted by JSK333
Well, it's not dipping with the 75HP jets. [/But I'm still getting knock retard, albeit less.

I might try different plugs. I have Autolite 104s gapped at .040". Maybe I'll try the 103s...QUOTE]

You need a new pump for the 125 then........

The 104s should be fine.

Do you have any knock retard when running NA?

 

No knock when running NA, nope. Only happens occasionally on the spray, but more often than not. And less with the 75-shot than the 100, 125 and 150 shots (when I logged them in the past).

Just for fun, I tried out the 150-jets again today and the FP dipped pretty good then came back up and dipped again. So obviously the stock pump is not up to much more than 75. I haven't checked the FP with the 100-jets yet, but I imagine it'll stay steady.

Any ideas why I'm getting knock even with the smallish 75-shot? I know NX says you don't need to take any timing out even up to their 150-shot, so it seems odd to me...

Thanks for your input.

I'm going to be looking for an intake pump that can support 800-900rwhp, as I know that'll be the max I'll ever want to make N/A + n2o combined.

Any recommendations?

 

Ild pull a couple of degrees of timing and give the 100shot a try with and without timing pulled. Are you running the stock ignition?

 

Well, the 100-shot dips the FP for a sec too. I can't hardly believe it! Is there any chance changing the 3-yr old fuel filter would improve fuel flow noticeably?

I'm using an Accel 300+ ignition with their 9000+ wires and Super coil.

I have no easy way to pull timing... so I guess I could reflash my PCM and pull it that way (which would affect N/A too, but at least tell me if less timing would help).

I'll report back with the results.

Solomon

 

Just pull it in the 3000+ rpm range v. 95+ kpa(WOT). I would also consider getting an aftermarket ignition to get a better spark.

 

As I mentioned, I already have an Accel 300+ digital ignition. I'll try pulling the timing sometime soon.

 

since your FP sending unit is b4 the noid, a fuel pressure drop should be expected when the noid opens(the close the sending unit is to the noid, the more drop it will see). However, after a short time the pressure should build up to acceptable levels. If this is what is happening then it should be normal. If your pressure doesn't go up then you have a problem...........

 

Well, I hope you're right.

The FP does come back up to where it should be (43.5) after it dips, so I guess it's just the sudden volume demand on the fuel pump from the noid opening, like I thought and you said.

The sender is actually on a T with the noid so it's not really "before" it. Do you think it'll still produce the same effect of dipping?

 

Well, I guess the knock is real.

I finally ended up pulling the equivalent of 2* from the stock tune, so I was then running about 30-31* of timing from 3000+ when the n2o hits.

And I would occasionally get ~500 counts of knock, although one time I got none.

So, I find this unacceptable, seeing how it's only a 100 shot on a stock engine, with aftermarket ignition.

Do you guys think different plugs/gap would change things? I'm running Autolite 104s @ .040" right now.