I'm running a TNT 150 wet shot on my MS3 cam only motor. To help with the fueling, I've added a Racetronix pump and hot wire kit, but the car still uses the stock 28lb injectors/rails. On the dyno this wasn't a problem as the kit was rich rich rich (for a graph, click here). I seem to be having a small issue with fuel pressure on the spray though.

During normal operation (on motor) the car averages anywhere from 58-61psi (per my Dynotune gauge). While spraying, the fuel pressure will drop to low 50s/high 40s on the gauge. Is this normal? An injector/rail upgrade is in the planbook for over the winter, but I want to run a few bottles through it before I put it away for the season.

The lowest I've seen the fuel pressure go is 48, it mostly stays around 50 even until we stop spraying.

What do you think - spray and be happy, or use caution? Thanks guys.

 

downfall of a returnless fuel system...an accumulator or regulator type system would be more stable

 

If I remember correctly the TNT kit is rated at 50psi fuel pressure so not a real problem there, but it sounds like you are running on the edge with your current fuel system. (shoudlnt be with the racetronics) Have you changed the fuel filter lately?

 

Dont mean to hijack your thread but I just was going to ask the same question. I am running a CF system and at times my Fuel pressure drops to about 52psi. I just changed my fuel filter and it seems same drop when I spray. From what I read here the danger zone seems to be anything below 50psi. With 92k on my motor I believe a new (racetronics) fuel pump is needed. I have been told that it will keep the pressure at 58-60 with that fuel pump.

 

Even without nitrous, I see a regular fuel pressure drop from 58 psi down to 52 psi under WOT, new fuel filter and all. I'll see what it does with my larger injectors, but I'm not holding my breath. It runs just fine, and I don't have a problem keeping it rich enough, but my injector duty cycle is at 90% on my stock internal car because of the drop.

 

mine drops to 58 with the same setup as yours at wot. On a 100 shot it drops 10psi.
I use the jet chart for 48-55 psi instead of 55-60 but it was still lean. Had to go even bigger to compensate for the lack of pressure to the injectors too.
I can't use the second stage because of fuel pressure so this winter a dedicated cell

 

Yes, the reg and return at the rails will cure the pressure drop at highest demand, and likely get rid of your small lean spike upon activation. Your a/f graph though is fine, you actually start going richer at the end of run, after the rails catch up. Imo, It's a good safety move to do the rails/reg mod, and has eliminated press drop and lean spike on my car with a 250rwhp shot.
Robert

 

Not normal, with the Racetronix kit you shouldn't go lower then 57 psi on the spray. If you can get a good mechanical fuel gauge on to monitor do it and see how much of a drop you get.

Matt

 

a voltage blaster would help.
do you have an underdrive pulley

 

This is a concern of mine when I put nitrous to my car. I have a racetronix setup, running green top innjectors and everything is o.k. on motor, fuel pressure was fien on the dyno. I'm running the stock 2001 rails/etc... are these dip issues related to the older fual rail systems in ls1's or does it apply to all years? I was planning on putting a NOS plate kit on the car and hitting it with 125 to start, I don't ever plan on running any more then 200 thru it so I'm not going crazy, but a fuel pressure drop off is my main concern at this point. If I have to put a standalone in to prevent it I will do it up front to save any problems I will... I just don't want to take any uneeded risks when I put the bottle to it.

 

Only the '97 and '98 C5 came with the return and reg at the rails. yes a stand alon can be another fix. We carry a stand alone that requires no relocation.
Nitrous Direct Stand alone
Robert

 

Do you have a pic of that setup installed, and can it be fitted with a high pressure pump? Only reason I ask is because the plate kit jetting is usually for high pressure fuel setups.

 

Normal driving pressure for me is 59ish psi on my dynotune gauge.. on a 150 shot, it falls to 54-55. I am in desperate need of a dedicated fuel system lol.