How To Tune Fuel Pressure For Nitrous

Zex Nitrous System With Fuel Pressure Gauge

If you care about how nitrous and gasoline combine to make excellent power, this story is for you. This is not revolutionary information-but it is one of the best ways to keep your nitrous engine healthy and powerful.

All nitrous systems are designed to use a combination of fuel and nitrous jets that are based on specific nitrous and fuel pressures. This is because reducing either fuel or nitrous pressure also lowers total flow. The opposite is also true: The same jet size will flow more fuel (or nitrous) at a higher pressure. This is why fuel pressure is so critical.

With a closed-end or dead-head nitrous fuel system, the fuel pump pushes fuel up against a closed valve when the fuel solenoid is not activated, which increases the line pressure, causing what is called fuel pressure creep. Most fuel pumps have an internal bypass that is set to a given pressure, which is usually higher than the nitrous fuel system flowing pressure. When the nitrous system is activated and the fuel solenoid opens, the pressure drops significantly. This is why nitrous fuel pressure must be set by creating system fuel flow. There is a cool tool from Zex that makes performing this test easy, so we chose to try it out on a small-block Mustang owned by Greg Smith. The car is equipped with a rear-mounted Holley blue pump and a 3/8-inch pickup in the tank connected by a -6 braided steel line up to the Holley fuel pressure regulator that is plumbed to the inlet side of the nitrous solenoid.

Measuring fuel pressure under simulated load conditions requires an accurate, high-quality gauge. The Zex kit uses an excellent Winters liquid-filled 0-15-psi gauge that is accurate to + or - 0.04 psi. The kit also comes with four fuel jets: 0.043, 0.064, 0.083, and 0.125 inch. Check it out.

PARTS LIST
DESCRIPTION	PN	SOURCE	PRICE
Zex fuel flow kit	82244	Summit Racing	$158.75

Plumbing the Zex gauge in line with the same gas jet used in the nitrous system will simulate the fuel flow and allow you to accurately set the fuel pressure.
Plumbing the Zex gauge in line with the same gas jet used in the nitrous system will simul
The Zex kit includes an accurate Winters liquid-filled 0-15-psi gauge, braided lines, a simple AN T, -6 and -4 male-to-male fitting adapters, and four fuel jets.
The Zex kit includes an accurate Winters liquid-filled 0-15-psi gauge, braided lines, a si
The jet acts as a flow restrictor. Inside the female hose end at the end of the kit's -4 braided line is a small brass fitting that retains the fuel jet.
The jet acts as a flow restrictor. Inside the female hose end at the end of the kit's -4 b

We used a 5/8-inch box-end wrench to loosen the lock nut on the fuel pressure regulator and used the Allen wrench to adjust the pressure. Turning the Allen adjuster clockwise increases pressure, and counterclockwise reduces the pressure.
We used a 5/8-inch box-end wrench to loosen the lock nut on the fuel pressure regulator an
Here is the Zex tool set up on the engine with the male-to-male -6 fitting connecting the gauge T to the fuel line that exits the fuel regulator. We checked for leaks and then fired up the pump with the engine off.
Here is the Zex tool set up on the engine with the male-to-male -6 fitting connecting the
With the pump pushing fuel past the nitrous jet into the plastic gas catch can, we adjusted the pressure to what Greg wanted, a safe 6 1/2 psi. We experimented with the regulator and noted that half a turn on the regulator was worth a 1/2-pound change in pressure. We discovered that the tiny gauge mounted on the regulator wasn't accurate. Our Winters gauge registered 6.5 psi when the little gauge read about 8 1/4 psi. That's a 27 percent difference on the lean side. We also measured the static, nonflowing pressure at 8 psi.
With the pump pushing fuel past the nitrous jet into the plastic gas catch can, we adjuste