7.8 Advanced Engine 7 ADDITIONAL ITEMS: BEYOND BASIC FUEL AND IGNITION CONTROL
7.8.15 Nitrous system
Nitrous oxide injection is primarily used in racing applications where nitrous oxide and additional fuel are injected
into the intake to give a horsepower boost. This is particularly popular in drag racing. Used correctly, nitrous
can give perhaps 100% additional power. Used incorrectly, it can melt pistons and destroy engines in seconds.
The nitrous system within MS3Pro allows control over the nitrous and optional fuel solenoid to enable the nitrous
injection when desired and also retard the ignition timing. The system supports two stages of control with on/off or
progressive.
There are two main categories of nitrous systems - wet and dry. You can further subdivide this into on/off,
progressive, and multistage nitrous systems.
7.8.15.1 Wet flow nitrous A wet system injects fuel into the manifold ahead of the injectors. This can result
in fuel distribution problems and mixture varying between cylinders. The simplest example of a wet system is a
"plate" system that installs under the throttle body (or carb) above the intake manifold and delivers nitrous and
fuel through spray bars. Other variations exist which use single or multiple nozzles. A standalone wet nitrous
system has the advantage that when used with the suppliers suggested jetting it will typically install and work.
More hardware, less tuning.
7.8.15.2 Dry nitrous With a dry system, the fuel injectors supply additional fuel when the nitrous is active.
Systems designed to work with OEM engine management sometimes do this by increasing fuel pressure, which
does not give accurate fuel increase across the rev range, but with MS3Pro, we can directly increase the injector
pulse width instead. The nitrous enters through a nozzle typically located upstream of the throttle body.
In a port-injection system, a dry nitrous system minimizes the fuel distribution problems. A dry system can
also have fewer system components, as it uses the existing fuel system components. However, because the fuel
and nitrous can be controlled independently, the software settings are critical to getting the mixture correct. Less
hardware, more tuning.
7.8.15.3 On/Off With On/Off control, the nitrous/fuel solenoids are either on or off. This is the standard operat-
ing mode.
7.8.15.4 Progressive control The Progressive system allows you to pulse you solenoids with output duty vary-
ing with rpm or time during drag pass. It is more complicated to setup than the On/Off system.
7.8.15.5 Multistage and progressive nitrous Note! - you are advised to always start with a simple system
using small jets. Big hits with multiple stages or progressive are significantly more difficult to install and tune
correctly.
With a single on/off stage using fixed jetting, the flow of nitrous (and fuel) is approximately constant under all
conditions. This means that if you are getting a claimed 100hp at 3000rpm when you activate the system, by
6000rpm the engine is turning twice as fast and each intake event will only receive half the nitrous/fuel, so you will
get half the torque benefit. One answer might be to use two stages based on rpm. The first stage is still jetted at
100hp, but at 4500rpm you bring in a second stage of say 25hp. This will make up for some of the "lost" torque.
Another approach would be a single stage progressive system using "200hp" jets. You could start at ~50% duty at
3000rpm and ramp up to 100% duty at 6000rpm. This could keep a similar torque gain across the rev range.
7.8.15.6 Tuning considerations In general, applying up to 50% extra hp to your engine with a kit manufac-
turer’s jetting and suggested retard works well and will not cause problems to your engine. However, it is very
important to take plug readings and check for any signs of leanness or detonation. As mentioned already, it is
quite easy to destroy your engine with nitrous given the wrong combination.
Easy mistakes to make with bad consequences:
• Mixed up fuel/nitrous jets.
• Fuel pressure too low (mismatched to fuel jet size)
• Incorrect dry fuel pulsewidth
AMP EFI MS3Pro manual version 1.202, firmware 1.5.0, 4/21/2017 Page 248
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