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supercharger, nitrous, and fuel pressure

I have a 90 mustang with 9psi procharger and a 75HP NOS dry kit. I'm still running stock 19lb injectors, but have updated the in-tank pump to 190lph in addition to the 260lph (I think) external pump that comes with the supercharger.

When running just the supercharger at 9psi, I'm at around 90psi fuel pressure. I understand this is OK. Now, with the 75HP nitrous, the fuel pressure meter is pegged. This is somewhat disconcerting for a couple of reasons:

  1. I have no idea what my fuel pressure is. (I'd guess 130psi)
  2. I'm worried that the stock lines can handle the pressure.

The car runs great, so I'm not really concerned that it's running lean, I'm more concerned about it running rich.

Do I have too much fuel pump for my configuration? Should I be able to run 9psi + 75HP without exceeding 100psi fuel pressure? Would moving to larger injectors/MAF sensor help (I don't see how it would since changing the injectors doesn't affect fuel pressure, only on-duration)?

If I go with larger injectors and keep my stock computer, this means my injectors will be open for the same amount of time for a given condition, but will flow more fuel than the smaller ones. Correct? That means I can reduce my fuel pressure considerably, right? (I do have an adjustable regulator and FMU)

Anyone out there doing something like this?

Thanks!

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Reply to
Edgar Circenis
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This much fuel pressure is rediculously high. You're probably not metering fuel very accurately as fuel injectors operate as designed in a range of 40-60 psi. I personally wouldn't run more than 60 psi in any senario.

Anything above 90 psi would give me cause for concern.

You need to be way more concerned with running lean than running rich. Running lean can kill your engine in the blink of an eye. Running rich just makes the car a dog but at least the chance of severe damage is limited to a degree.

You need 30# fuel injectors at a bare minimum and I recommend getting

42's. While you're doing this get a new MAF calibrated for the new injectors. You're probably on the verge pegging the stock MAF, if it isn't already pegging.

You might be able to get by without a custom chip if you get the MAF calibrated for the new injectors. It just depends on the car.

I have a blown '89 LX and one thing you don't want to do on a supercharged engine is to run lean or have too much timing. These contribute to detonation which kills motors very quickly. Don't go cheap on the fuel system parts or you'll likely regret it.

Reply to
Michael Johnson, PE

Switch to a Wet Nitrous kit instead of the dry. Though you prolly already know this.. When you use a dry kit the motor gets more fuel by increasing the fuel pressure. If you use a wet kit there are seperate lines ran for the fuel and the nitrous so the fuel pressure doesnt increase.

Reply to
John R Wiebalk

Reply to
James

Thanks, everyone, for all the advice. After thinking about it overnight, I'll probably get 30# injectors, a new MAF metering tube, and start dinking with the regulator and FMU to lower the pressure. Any suggestions for idle fuel pressure with 30# injectors?

I have a procharger P1SC. Do I have to get some kind of one-way valve for the FMU vacuum line so I don't leak vacuum through the needle valve (now that I will be opening it)?

As for timing, it's stock 10 degrees. 91 octane (at 5000 feet elevation). No detonation. I'm guess it's good I haven't burst a fuel line or broken the engine. Anyway, no more nitrous until I get the fuel pressure down.

On another topic, has anyone with a P1SC gone to a smaller blower pulley? How did that work out?

Thanks!

Reply to
Edgar Circenis

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