Nitrous oxide jet Chart


I have a 1992 Olds Achieva with a highly modified W41 Quad 4. It has been fortified with forged Eagle rods, forged Wiseco pistons, an Evans Cryo-REMed crank, ported heads, and 42-lb/hr fuel injectors. I want to put together a 200hp-shot direct-port wet nitrous system for it. My biggest concern is how to tap into the stock fuel system. I have swapped in an in-tank TRE 255-lph high-pressure fuel pump. I already have a 15-pound Zex Blackout nitrous bottle and brackets. 2/5 If the existing fuel pump and fuel lines have sufficient capacity, auxiliary fuel for the nitrous system can be supplied via the fuel-injection rail test-port. Inside the test-port is a Schrader valve similar to the valve used on a tire’s valve-stem (arrow).


The method used to supply auxiliary fuel for a nitrous oxide system used on an engine with electronic fuel injection (EFI) depends on the type of nitrous system, as well as its projected power level. A direct-port fuel-injection engine can utilize one of several different basic nitrous oxide system configurations: dry, wet single-point, or wet multipoint.

In a dry nitrous system, the extra fuel required to support the nitrous shot is introduced through the existing electronic fuel injectors. No fuel flows through the intake manifold plenum or runners (that’s why it’s called a “dry” system).What’s The Best Way To Supply Fuel To A Wet Nitrous Oxide System On A Multi-Port EFI Engine? In a dry system, fuel flow can be increased by raising the fuel-injection system pressure or by reprogramming the ECU to increase the fuel injectors’ dwell-time (the period the fuel injectors remain open). The auxiliary nozzles on this type of system spray nitrous only. Usually the nitrous oxide nozzles spray through the mass airflow (MAF) sensor, which assumes it’s seeing colder, denser air, and sends a signal to the ECU to supply more fuel.

In a wet single-point system, fuel and nitrous are introduced together via a combined nitrous and fuel fogger-style nozzle. Usually on a fuel-injected application, the nozzles are fitted to a plate that mounts between the throttle-body and intake manifold, or in a modified inlet duct leading to the throttle-body.

Unscrew ValveIn a wet nitrous system (aka a direct-port nitrous system), nitrous and fuel are introduced directly into each inlet port near the cylinder-head end of the manifold’s runner. There can be one combo nitrous and fuel nozzle in each runner or a separate nitrous and fuel nozzle for each runner.

A dry system is generally recommended for entry-level applications on a stock- or near-stock, normally aspirated engine up to about the 150hp-shot level. The problem is that relying on the MAF to tell the computer more fuel is needed when you hit the nitrous button is relatively inexact and is subject to system lag as the amount of nitrous injected into the engine increases. As power levels go up, sophisticated ECU reprogramming is required, and even with new tuning it is usually difficult to achieve consistent power gains at higher nitrous power levels.

Wet systems meter nitrous and fuel through jets with different orifice sizes. For the average hot rodder, this makes it easier to fine-tune the proper air/fuel ratio. Sophisticated computer reprogramming skills are not critical. However, on a single-port wet system, there’s a definite limit to what can be accomplished when installing such a system on factory-style EFI intake manifolds that are usually designed to flow air only, with smaller orifices and relatively sharp edges and turns compared to, for example, an old-school carburetor-style manifold that was designed to flow both air and fuel. That’s because fuel, being heavier than air or nitrous, has a hard time when in motion; it doesn’t like to turn corners due to its greater inertia. The fuel may separate from the air, and the nitrous from the fuel. This can cause backfiring or a lean condition in one or more cylinders.

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