Fuel pressure at high altitude. etc...

[Dark_5.0]

I am having hell finding just the right fuel pressure for my speed density stang....

MY THEORY the stock fuel pressure is set at 39psi....If you go up to say 3000ft the car would actually be running a lil' rich, and you could actually gain HP by cutting back the fuel pressure.

Some of the people on this board have almost the exact same mods as me and run 44-45psi of fuel pressure......My car seemed like it performed better at 42-43psi.....I am asuming that my car likes less fuel pressure cause I am making less HP cause of the altitude.

Nitrous also seems to knock more time off at high altitude than it does at sealevel.....I am assuming that this is do to the fact that nitrous makes Oxygen as a buy product wich counteracts the thin air.

I am just thinking out loud......and trying to figure out if the fuel to nitrous ratio is going to be different at high altitude compared to sea level....Since nitrous has a greater effect on cars at high altitude than at sea level IMO

I would like to here what people think good or bad.

Later,

[red82gt]

You're right about running rich @ altitude, don't be afraid to go back to stock fuel pressure, the stock fuel pressure supplies enough fuel for 300hp at seal level. You're right about the nitrous too, it supplies it's own oxygen so you've always got near optimum air with nitrous. Since the amount of oxygen in the nitrous is always the same, the amount of fuel will be the same too. As far as I know the only condition for changing the nitrous/fuel ratio would be the bottle pressure.

[buffhomer]

I live in Artesia and run in Roswell (elevation 3600ft) New Mexico. My mods are not quite as extensive as yours:

1 5/8" shorties
2 1/2" off-road exhaust w/2-chambers
pullies
3.73s
short belt
gasket matched stock heads w/smog bumps removed
C&L 76mm MAF

I've gone 13.24@102 in Roswell with the stock fuel pressure. Dyno in Phoenix with stock fuel pressure put out 250rwhp, or 300 even at the crank basically. One thing we've found with the Stangs here is that stock fuel pressure is fine until you get to ~105 or so. My advice to you is keep the stock pressure, and if you wanna lean it back, learn to read the plugs, but preferably if you can get it dyno tuned then do that.

As for the nitrous/fuel issue, I'm not sure I understand what you're asking, I'll just say to stick with the recommended jet sizes and you'll be ok. FYI I run an NX wet kit on my stang.

[Dark_5.0]

Correct me if I am wrong but dont the mass air mustangs raise the fuel pressure on there own when they since more air flow.

Speed density mustang do not since airflow so they do not macth the added airflow with extra fuel, so I have to do it manually by bumping my fuel pressure up to 42-43 a WOT...

Is that correct on no..

Later,

[red82gt]

The mass air mustangs lengthen the pulse width to add more fuel to match the air coming in, the fuel pressure stays constant.

I'm not sure, but I think the SD computer can still control pulse width for part throttle from the O2 sensors and add a correction to the fuel tables. Upping your fuel pressure will add more fuel at WOT but you may not need it at your altitude. Remember, these things do run quite rich from the factory as a safety net.

[PKRWUD]

Also, the ECM is adaptive, and regardless of where you set the pressure, it will eventually do what it has to to bring things back to it's preprogrammed "normal". Problem is, by then you may have caused damage with an overly rich mixture.

Take care,
-Chris